Water, OH and methanol masers in SFRs

Water masers accompanying OH and methanol masers in star formation regions

Abstract

The Australia Telescope Compact Array (ATCA) has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFR)s in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries and others had been reported, with position uncertainties exceeding 10 arcsec, from Parkes telescope single dish observations many years ago.

Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds.

The precise water positions show that approximately 79 per cent (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water masers coincide with a 1665-MHz ground-state OH maser counterpart. Our less uniform sample of methanol targets is not suitable for a full investigation of their association with water masers, but we are able to explore differences between the velocities of peak emission from the three species, and quantify the typically larger deviations shown by water maser peaks from systemic velocities.

Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. We also report the detection of ultracompact H ii regions towards some of the sites. In combination with an investigation of correlations with IR sources from the GLIMPSE catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.

keywords:
masers - stars: formation - H ii  regions - ISM: molecules - radio lines: ISM.
12

1 Introduction

Masers of OH (hydroxyl), water and methanol are key tools for investigating the formation of massive stars. The masers reside in the dusty molecular envelope or torus of a massive star in its earliest stage of formation, and the masers are a sensitive probe for discovering stars in this embryonic state when the star is not visible because of obscuration from the dust.

Detailed studies of selected maser sites have been made comparing OH with water, and OH with methanol (Forster & Caswell 1989, 1999; Caswell 1997; Caswell Vaile & Forster 1995; hereafter FC89, FC99, C97, CVF95). These suggest that the maser spots of all species are usually contained inside a region of diameter less than 30 mpc (= m = cm au light year), corresponding to an angular diameter of about 1 arcsec at a typical distance of 6 kpc. Positional precision of about 1 arcsec is therefore desirable to establish whether masers of different species originate from the same site.

Within many star formation regions (SFRs), on a larger scale of 100 mpc or more, the FC89 and C97 studies revealed many instances where a number of maser sites are present in a small cluster, often with different combinations of maser species present. There has been considerable speculation that the various combinations are indicative of massive young stars at a different evolutionary stage, or in a different mass range (e.g. Breen et al., 2010; Ellingsen et al., 2007). Water maser emission is especially puzzling. It has commonly been thought to be most prolific at an early stage of stellar evolution, but isolated water masers are only partly accounted for by very young sites preceding OH maser excitation. Other offset positions indicate the additional occurrence of water masers towards lower mass stars, or in high velocity fragments that have travelled far from the initial site. In the latter case, maser spots from individual fragments are sometimes ephemeral, and disappear on a timescale as short as months, but are often replaced by generally similar emission in the same region, although at a slightly different position and velocity.

To date, the most extensive unbiased survey for masers of the SFR variety completed in the Galactic plane is at the 1665-MHz transition of OH, presented as a catalogue reporting positions of arcsec accuracy for more than 200 masers (Caswell 1998; hereafter C98). Sensitive observations of 6.6-GHz methanol at these positions have already been made, with a detection rate of 80 per cent after high precision positions are compared (Caswell, 1998, 2009). Early 22-GHz water maser surveys with the Parkes radio telescope towards southern SFRs have been reported by Caswell et al. (1989) and references therein, with positions measured to about 10 arcsec accuracy. Until recent years, follow up observations to arcsec accuracy were restricted to northerly objects accessible to the VLA (FC89, FC99). The availability of the 22-GHz frequency band at the ATCA has allowed us to search with high sensitivity and high positional precision for water masers towards the full sample of OH masers, as well as 100 methanol maser sites.

2 Observations and data reduction

Water maser observations were made with the ATCA on two separate occasions. During the first epoch of observations (2003 October 4 and 5), OH maser sites from C98 were targeted (see also Section 5.3) and during the second epoch (2004 July 25, 26 and 30) many water maser detections towards the OH masers were re-observed as well as a selected set of methanol masers (chiefly from Caswell, 2009). OH maser sources that were targeted in the first epoch but showed no detectable water maser emission were not observed at the second epoch, and only a few of the water maser sources that had previously been observed by FC89 with the VLA, and successfully confirmed during the first epoch, were reobserved.

Our first observations were made with an EW array yielding 10 baselines between 30 and 352 m (project c1190). The correlator sampled a single linear polarization, processed to give a 512-channel spectrum across a 32-MHz bandwidth. The observing strategy was to observe approximately 100 targets over each 12-h session. After initial calibration, the first 10 targets were observed for 1.5 min each, followed by a calibrator, and similarly for the remaining 90 targets. Then the cycle was repeated 2 more times, so as to provide for each source adequate uv-coverage, combined with a total integration time of 4.5 min. Primary flux calibration is relative to PKS B1934-638 and in general is expected to be accurate to 20 %. PKS B1921-293 was used for bandpass calibration.

The AIPS reduction package was used for processing of the data collected in this first epoch, following the general procedure described in C97. In the realignment of channels using the CVEL task, the adopted rest frequency was 22235.08 MHz, and the velocity scale was with respect to the local standard of rest (lsr). The channel separation was 0.84  which, with uniform weighting of the correlation function, yields a final velocity resolution of 1.0 . The quite coarse resolution was a compromise chosen in order to allow a large velocity coverage of more than 400 . With this coverage, it was possible to recognise any high velocity features indicative of close association with outflows (for which the water masers are renowned).

Total intensity maps were then produced of the channels with maser emission apparent in the scalar averaged spectrum, or in a vector averaged spectrum shifted to the location of the target OH or methanol maser emission. The rms noise in an individual channel image was typically 150 mJy. The synthesised beam has a halfpower width of approximately 8 arcsec in right ascension, but is larger in declination by a factor cosec(declination) as expected for an array aligned East-West with maximum baseline of 352 m.

Our second series of observations (project c1330) were made in similar fashion but with a different array configuration, H168. The correlator configuration, and therefore the spectral resolution and velocity coverage, was identical to that used in the 2003 observations. A few sample observations from this epoch were reduced, firstly with AIPS (as for the 2003 data), and secondly with miriad software package (Sault, Teuben & Wright, 1995). There was excellent agreement between data reduced in the respective data reduction packages. The full data set from this epoch were reduced using miriad, applying the standard techniques for ATCA spectral line and continuum observations. Image cubes of the entire primary beam and velocity ranges were produced for each source. The flux densities of sources that were located away from the centre of the primary beam have been corrected to account for beam attenuation. Spectra for each source detected at this epoch were produced by integrating the emission in the ATCA image cubes for each source. The typical resultant rms noise in each spectrum was 40 - 50 mJy. For the H168 array used in 2004, the synthesised beam was typically 13x9 arcsec.

The ATCA observations are most sensitive at the targeted positions, but provide useful measurements, albeit at lower sensitivity, of any other sources that happen to lie within the field of view of the primary beam; the full width to the first null is nearly 5 arcmin, and the HPBW is 2.29 arcmin = 137 arcsec.

Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 240.316+0.071 07 44 51.94 –24 07 41.9 89 58,100 10 o
G 263.250+0.514 08 48 47.91 –42 54 27.1 19 17,21 3.0 20 17,21 0.7 om
G 284.350–0.418 10 24 10.60 –57 52 33.0 –4 –42,72 60 7 –78 ,71 102 o
G 285.260–0.067 10 31 24.57 –58 03 03.7 –28 –95,20 22 –92 –96,20 30
G 285.263–0.050 10 31 29.64 –58 02 18.9 2 –59,50 1100 3 –36,63 1651 o
G 287.371+0.644 10 48 04.25 –58 27 00.7 1 –14,6 3.5 –1 –13,1 4.9 om
G 290.374+1.661 11 12 17.98 –58 46 21.6 –12 –20,–10 3.5 –47 –47,–33 0.26 om
G 290.384+1.663 11 12 22.53 –58 46 29.0 –38 –50,–35 6 –37 –41,–35 4.5
G 291.270–0.719 11 11 49.67 –61 18 53.8 –102 –110,–23 65 –102 –109,–17 53 m
G 291.274–0.709 11 11 53.28 –61 18 24.1 –32 –51,14 60 –32 –59,–14 64 om
G 291.284–0.716 11 11 56.58 –61 19 01.1 –133 –142,–120 930 –133 –139,–120 701
G 291.578–0.434 11 15 04.91 –61 09 50.7 0.2 18 17, 27 16
G 291.579–0.431 11 15 05.67 –61 09 41.0 12 –29,41 215 13 –31,22 608 om
G 291.581–0.435 11 15 06.17 –61 09 56.1 26 25,27 4.0 0.2 m
G 291.610–0.529 11 15 02.58 –61 15 48.8 13 –66,20 18 12 –66,28 39 oc
G 291.627–0.529 11 15 10.18 –61 16 12.7 22 8,23 12 22 20,25 31
G 291.629–0.541 11 15 08.88 –61 16 54.8 11 8,16 70 10 –2,21 46
G 294.511–1.622 11 35 32.04 –63 14 44.3 –12 –20,–6 250 –12 –20,–4 112 om
G 294.976–1.733 11 39 13.77 –63 29 03.3 1 –17,5 2.2
G 294.989–1.719 11 39 22.56 –63 28 25.1 –17 –18,–10 0.6 m
G 297.660–0.974 12 04 08.76 –63 21 37.3 29 –80,38 90 26 –79,82 75 o
G 299.012+0.125 12 17 24.05 –62 29 13.6 0.2 –26 –27,–24 0.44
G 299.013+0.128 12 17 24.58 –62 29 04.8 19 18,30 100 19 –1, 50 83 omcg
G 300.491–0.190 12 29 55.99 –62 57 33.8 24 23,25 2.3 25 22,25 1.6
G 300.504–0.176 12 30 03.42 –62 56 50.2 11 –37,14 180 11 –26,14 94 omg
G 300.968+1.143 12 34 52.51 –61 39 57.9 –61 –86,–42 70 –58 –86,–3 26
G 300.971+1.143 12 34 54.34 –61 39 57.1 3 –43 –46,–42 3.0
G 301.136–0.225 12 35 34.76 –63 02 28.5 t –47 –48,–41 17
G 301.136–0.226a 12 35 34.93 –63 02 34.5 –29 –56,–18 80 –29 –31,–28 78 g
G 301.136–0.226b 12 35 34.84 –63 02 31.1 t –45 –63,–43 92 (omc)
G 301.137–0.225 12 35 35.21 –63 02 30.6 t –36 –40,–33 39 omc
G 305.191–0.006 13 11 12.95 –62 47 27.7 31 28,36 25 32 29,35 4.8 g
G 305.198+0.007 13 11 16.38 –62 46 37.4 –39 –42,–27 8 –35 –41,–24 3.5
G 305.208+0.207 13 11 13.37 –62 34 40.0 –39 –43,–37 300 –39 –44,–38 235 om
G 305.361+0.150 13 12 35.61 –62 37 18.9 –43 –45,–28 250 –36 –44,–29 126 omg
G 305.799–0.245 13 16 42.92 –62 58 31.7 –26 –45,35 400 –34 –119,37 266 omg
G 306.318–0.331 13 21 20.87 –63 00 22.7 –19 –24,–14 2.1 –18 –23,–15 0.7
G 307.805–0.456 13 34 27.32 –62 55 12.4 –13 –15,–7 1.4 –7 –11,–7 0.6 og
G 308.754+0.549 13 40 57.47 –61 45 42.4 –49 –50,–48 3.4 –49 –50,–48 0.7 omg
G 308.918+0.124 13 43 01.64 –62 08 48.9 –56 –66,–45 0.7 –61 –62,–49 1.5 om
G 309.384–0.135 13 47 24.01 –62 18 11.4 –50 –57,–41 3.5 –50 –51,–48 2.2 omg
G 310.144+0.760 13 51 58.53 –61 15 40.6 –58 –60,–55 2.5 –58 –59,–57 1.6 omg
G 310.146+0.760 13 51 59.61 –61 15 39.7 –63 –64,–62 8 0.2
G 311.643–0.380 14 06 38.77 –61 58 22.7 35 18,50 320 36 8,56 167 omcg
G 312.106+0.278 14 08 46.06 –61 12 30.1 –54 –55,–53 0.6 g
G 312.109+0.262 14 08 49.45 –61 13 23.4 –48 –48,–47 0.43 mg
G 312.596+0.045 14 13 14.13 –61 16 57.6 –61 –62,–58 0.6 –59 –64,–56 1.5 m
G 312.599+0.046 14 13 15.19 –61 16 51.9 –75 –102,–58 2.7 –79 –96,–56 9 om
G 313.457+0.193 14 19 35.05 –60 51 54.2 –1 –2,0 1.9 45 –1,46 1.0 c
G 313.470+0.191 14 19 40.97 –60 51 46.2 –5 –10,–2 6 –6 –10,–1 4.5 omg
Table 1: 22-GHz water masers detected towards sites of OH and methanol masers. Column 1 shows the source name in Galactic coordinates, column 2 and 3 give the right ascension and declination, column 4, 5 and 6 give the velocity of the water maser peak, velocity range and peak flux density in the 2003 observations, while columns 7, 8 and 9 give the velocity of the water maser peak, velocity range and peak flux density in the 2004 observations. A ‘–’ in either column 6 or 9 indicates that no observations were made of the given source during the 2003 or the 2004 epoch, respectively, while the presence of a number preceded by a ’’ indicates that there was no emission detected above the quoted threshold. For some complicated sources a ‘t’ is present in either column 6 or 9 and this indicates that the exact nature of the detection is discussed in Section 4. Associations are given in column 10, where the presence of an ‘o’ denotes an OH maser, an ‘m’ denotes a methanol maser, a ‘c’ denotes the presence of a 22-GHz radio continuum source, a ‘g’ the presence of a GLIMPSE point source and the presence of a ’’ indicates that the water maser source is outside the range of the GLIMPSE survey region. A ’’ indicates that the proceeding associated source is strictly outside our association threshold but has been added through special circumstances. See Section 3 for a more extensive description.
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 313.578+0.325 14 20 08.63 –60 41 59.0 –46 –58,–32 55 –47 –54,–32 46 omg
G 313.767–0.862 14 25 01.71 –61 44 57.2 –54 –56,–48 160 –54 –57,–36 162 omg
G 314.320+0.112 14 26 26.37 –60 38 29.4 –44 –70,–40 34 –45 –70,–40 16 om
G 316.360–0.361 14 43 11.07 –60 17 10.3 3 –4,21 30 3 –7,20 16
G 316.361–0.363 14 43 12.22 –60 17 16.6 –3 –4,–1 6 –3 –7,–1 2.6
G 316.412–0.308 14 43 23.22 –60 12 58.8 –22 –30,6 6 –20 –24,5 15 omcg
G 316.640–0.087 14 44 18.39 –59 55 10.7 –19 –104,–2 12 –15 –40,92 12 omg
G 316.763–0.011 14 44 56.32 –59 47 59.8 –47 –51,–33 60 –48 –49,–33 4.1 og
G 316.812–0.057 14 45 26.58 –59 49 14.1 –46 –47,–36 500 –46 –56,–11 408 om
G 317.429–0.561 14 51 37.72 –60 00 18.2 16 12,25 0.5 25 24,25 0.27 oc
G 317.429–0.556 14 51 36.75 –60 00 03.4 26 25,36 0.5 28 27,29 0.6
G 318.044–1.404 14 59 08.61 –60 28 23.9 42 31,44 3.5 42 32,42 3.5 om
G 318.050+0.087 14 53 42.62 –59 08 52.3 –55 –61,–39 470 –48 –69,–38 50 omg
G 318.948–0.196a 15 00 55.18 –58 58 51.6 –41 –44,–28 5 –36 –44,–27 9 g
G 318.948–0.196b 15 00 55.33 –58 58 53.6 t –38 –39,–21 7 omg
G 319.399–0.012 15 03 17.50 –58 36 11.4 –4.5 –20,1 10 –5 –7,2 3.8 oc
G 319.836–0.196 15 06 54.54 –58 32 58.6 –13 –23,0 9 –11 –19,0 2.8 omg
G 320.120–0.440 15 09 43.83 –58 37 06.3 –46 –70,–40 1.2 –46 –158,30 0.9 o
G 320.221–0.281 15 09 47.00 –58 25 47.6 0.4 –73 –75,–72 0.7
G 320.232–0.284 15 09 51.92 –58 25 38.0 –63 –70,–61 9 –67 –81,–72 2 om
G 320.233–0.284 15 09 52.50 –58 25 35.7 –60 –61,–58 3.5 –60 –61,–54 3.4 c
G 320.255–0.305 15 10 06.14 –58 26 00.8 –126 –144,–111 45
G 320.285–0.308 15 10 18.88 –58 25 16.5 –69 –81,–56 15 g
G 321.028–0.484 15 15 50.90 –58 11 19.7 –60 –70,–55 2.5 –58 –70,–52 5
G 321.033–0.483 15 15 52.60 –58 11 07.2 –60 –68,–58 3.6 –61 –64,–49 0.25 m
G 321.148–0.529 15 16 48.25 –58 09 50.1 –64 –66,–62 0.8 –97 –98,–61 1.6 omg
G 322.158+0.636 15 18 34.52 –56 38 24.7 –73 –81,–61 5 –76 –86,–65 2.7 om
G 322.165+0.625 15 18 39.74 –56 38 46.7 –40 –67,–36 9 –39 –67,–36 2.8 g
G 323.740–0.263 15 31 45.48 –56 30 49.6 –50 –72,–46 140 –50 –88,–42 70 omg
G 324.201+0.122 15 32 52.76 –55 56 04.9 –87 –100,–47 50 –87 –100,–48 14 o
G 324.716+0.342 15 34 57.41 –55 27 22.3 –55 –72,–47 10 –58 –81,–30 26 omg
G 326.662+0.521 15 45 02.73 –54 09 03.3 –39 –50,–34 256 m
G 326.665+0.553 15 44 55.82 –54 07 25.6 t –42 –127,–39 16 g
G 326.670+0.554 15 44 57.03 –54 07 10.6 –42 –44,–40 26 –40 –48,8 101 o
G 326.780–0.241 15 48 55.10 –54 40 38.6 –64 –66,–60 36 –66 –92,–52 18 og
G 326.859–0.676 15 51 13.82 –54 58 03.6 –103 –104,–103 0.42 mg
G 327.119+0.511 15 47 32.56 –53 52 39.3 –87 –90,–80 25 –88 –89,–57 19 omg
G 327.291–0.578 15 53 07.65 –54 37 07.2 –56 –80,–39 400 –63 –84,–36 668 omg
G 327.391+0.200 15 50 18.31 –53 57 06.1 –86 –92,–86 0.40 mg
G 327.402+0.445 15 49 19.32 –53 45 13.8 –80 –83,–68 230 –81 –84,–69 195 omcg
G 327.581–0.077 15 52 29.50 –54 02 51.6 –101 –102,–95 1.0
G 327.594–0.095 15 52 38.19 –54 03 11.5 –99 –102,–91 0.8 g
G 327.619–0.111 15 52 50.31 –54 03 00.0 –85 –85,–84 0.20 mg
G 327.935–0.123 15 54 33.09 –53 51 29.1 –98 –100,–76 2.1
G 328.236–0.548 15 57 58.21 –53 59 25.4 –38 –39,–37 30 –38 –40,10 20 omcg
G 328.254–0.532 15 57 59.69 –53 58 00.7 –50 –53,–48 200 –50 –51,–48 155 omg
G 328.306+0.432 15 54 05.91 –53 11 37.4 –96 –97,–87 40 –93 –96,–87 141 c
G 328.808+0.633 15 55 48.23 –52 43 05.2 –46 –47,–44 10 –46 –48,–44 4.4 omcg
G 329.021–0.186 16 00 24.32 –53 12 16.9 –42 –43,–41 2.4 –44 –44,–43 0.34 g
G 329.029–0.199 16 00 30.22 –53 12 34.3 –38 –40,–37 1.6 0.2 og
G 329.030–0.205 16 00 31.90 –53 12 48.7 –39 –54,–34 8 –46 –52,–35 6 om
G 329.031–0.198 16 00 30.34 –53 12 26.5 –39 –54,33 5 –52 –65,33 1.2 omg
G 329.066–0.307 16 01 09.89 –53 16 01.5 –48 –50,–47 1.4 –45 –46,–45 0.6 omg
G 329.183–0.313 16 01 46.90 –53 11 41.7 –51 –66,–36 24 –50 –60,–39 34 omg
G 329.342+0.130 16 00 38.87 –52 45 22.9 –112 –115,–95 1.1 –112 –114,–100 2.2
G 329.404–0.459 16 03 31.81 –53 09 30.8 –113 –117,–106 3.1 –113 –116,–111 2.4
G 329.405–0.459 16 03 32.15 –53 09 29.0 –78 –80,–60 15 –77 –79,–44 10 om
G 329.407–0.459 16 03 32.77 –53 09 25.0 –74 –76,–72 80 0.2 mg
G 329.421–0.167 16 02 19.85 –52 55 41.8 0.8 –77 –78,–75 2.4
G 329.424–0.164 16 02 20.03 –52 55 25.9 –78 –83,–60 0.8 0.2 g
Table 1: continued
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 329.426–0.161 16 02 19.71 –52 55 12.8 –73 –78,–71 8 –73 –74,–72 10
G 329.457+0.503 15 59 36.93 –52 23 53.6 –66 –68,–65 4.3
G 329.622+0.138 16 02 00.28 –52 33 57.7 –82 –110,–66 30 mg
G 330.070+1.064 16 00 15.56 –51 34 25.7 –50 –75,–45 11 m
G 330.879–0.367 16 10 20.04 –52 06 06.8 –64 –72,–28 90 –60 –72,–25 95 omc
G 330.954–0.182 16 09 52.65 –51 54 54.6 –80 –150,70 240 –91 –191,56 323 ocg
G 331.132–0.244 16 10 59.73 –51 50 22.5 –99 –102,–73 280 –99 –118,–55 47 omg
G 331.278–0.188 16 11 26.51 –51 41 55.8 –86 –104,–79 55 –90 –118,–64 42 omg
G 331.342–0.346 16 12 26.49 –51 46 14.9 –60 –62,–59 1.8 –62 –64,–60 11 omg
G 331.418+0.252 16 10 10.56 –51 16 52.2 –71 –71,–70 0.6 g
G 331.442–0.187 16 12 12.46 –51 35 09.3 –88 –93,–72 70 –88 –113,–80 212 omcg
G 331.512–0.103 16 12 10.01 –51 28 36.7 –89 –162,–33 700 –90 –159,–32 534 ocg
G 331.555–0.122 16 12 27.20 –51 27 42.6 –99 –170,–96 20 –99 –166,–86 9
G 332.094–0.421 16 16 16.68 –51 18 26.2 –59 –59,–58 0.29 m
G 332.296–0.094 16 15 45.84 –50 55 52.7 –50 –71,–43 6 m
G 332.349–0.433 16 17 30.03 –51 08 16.6 –67 –68,–67 2.9
G 332.352–0.117 16 16 07.10 –50 54 31.0 –45 –48,–41 2.0 –60 –61,–60 0.5 om
G 332.604–0.167 16 17 29.45 –50 46 11.7 –46 –48,–45 2.4 mg
G 332.725–0.621 16 20 02.91 –51 00 33.1 –42 –43,–41 0.6 –58 –59,–56 5 omg
G 332.826–0.549 16 20 11.17 –50 53 14.6 –56 –72,–30 45 –59 –71,–35 70 mc
G 332.964–0.679 16 21 23.03 –50 52 57.3 –52 –52,–50 2.9 mg
G 333.030–0.063 16 18 56.86 –50 23 53.6 –40 –153,–40 3.4 mc
G 333.055–0.436 16 20 42.47 –50 38 46.4 –47 –57,–48 0.39
G 333.114–0.439 16 20 59.30 –50 36 21.9 –62 –63,–60 4.6 –62 –62,–53 2.0
G 333.121–0.434 16 20 59.70 –50 35 50.8 –57 –59,12 38 –47 –91,–33 21 m
G 333.126–0.440 16 21 02.69 –50 35 54.1 –50 –70,–48 19 –52 –72,–47 12 m
G 333.128–0.440 16 21 03.18 –50 35 51.8 0.2 –124 –125,–124 0.79 m
G 333.130–0.425 16 20 59.75 –50 35 05.1 –39 –67,–38 23 –64 –65,–31 1.9
G 333.132–0.560 16 21 36.46 –50 40 45.4 –53 –67,–46 1.9
G 333.219–0.062 16 19 47.40 –50 15 53.8 0.3 –13 –14,84 0.5 g
G 333.234–0.060 16 19 50.85 –50 15 09.7 –88 –102,–83 140 –88 –102,82 117 og
G 333.315+0.106 16 19 28.75 –50 04 39.7 –48 –68,–41 2.2 –48 –60,–48 6 omg
G 333.387+0.032 16 20 07.52 –50 04 47.4 –61 –63,–60 0.4 –61 –61,–60 0.14 omg
G 333.467–0.164 16 21 20.20 –50 09 46.1 –44 –46,–40 3.5 –42 –47,–40 3.2 om
G 333.608–0.215 16 22 11.08 –50 05 56.3 –51 –76,–45 50 –49 –83,–41 24 o
G 333.646+0.058 16 21 09.12 –49 52 45.1 –89 –90,–84 3.3 m
G 333.682–0.436 16 23 29.67 –50 12 07.4 –3 –3,–2 0.24 mg
G 333.930–0.134 16 23 14.68 –49 48 48.8 –46 –50,–45 0.18 m
G 334.635–0.015 16 25 45.83 –49 13 37.0 –26 –29,–15 49 mg
G 334.935–0.098 16 27 24.22 –49 04 11.0 –17 –18,–14 1.0 mg
G 334.951–0.092 16 27 26.96 –49 03 14.7 –21 –25,–20 1.3
G 335.059–0.428 16 29 23.20 –49 12 31.3 t –38 –39,–37 1.7
G 335.060–0.428 16 29 23.24 –49 12 28.0 –46 –50,–37 12 –37 –44,15 3.0 omg
G 335.070–0.423 16 29 24.72 –49 11 47.7 –88 –109,–84 1.0 –90 –105,–84 5 g
G 335.585–0.285 16 30 57.34 –48 43 39.4 –45 –50,–40 30 –42 –49,–32 25 omg
G 335.586–0.290 16 30 58.73 –48 43 51.2 –48 –61,–33 5 –56 –57,–42 20 omg
G 335.588–0.264 16 30 52.52 –48 42 39.5 –51 –56,–48 16 0.2 g
G 335.727+0.191 16 29 27.52 –48 17 51.9 –51 –51,–42 13 m
G 335.787+0.177 16 29 46.18 –48 15 49.1 –55 –56,–48 3 .0 –49 –59,–45 10
G 335.789+0.174 16 29 47.33 –48 15 50.8 –46 –51,–45 3.0 0.2 omg
G 335.789+0.183 16 29 45.10 –48 15 30.4 –91 –112,–89 4.2 0.2
G 336.018–0.827 16 35 09.35 –48 46 47.7 –54 –59,–36 120 –54 –59,–36 82 omc
G 336.352–0.149 16 33 30.73 –48 04 27.6 –79 –81,–78 0.4 –79 –81,–78 0.43
G 336.359–0.137 16 33 29.37 –48 03 41.5 –67 –67,–66 0.5 0.2 omc
G 336.433–0.262 16 34 20.31 –48 05 30.5 –89 –90,–88 0.6 mg
G 336.496–0.258 16 34 34.52 –48 02 34.3 –25 –38,–14 8
G 336.830–0.375 16 36 26.19 –47 52 29.5 –20 –45,–19 0.28 mg
G 336.864+0.005 16 34 54.50 –47 35 37.7 –78 –80,–64 3.0 –66 –79,–65 2.2 om
G 336.864–0.002 16 34 56.02 –47 35 55.3 –73 –76,–71 4.5 –73 –77,–71 1.5
G 336.870–0.003 16 34 57.91 –47 35 42.7 –77 –78,–55 2.0 –77 –78,–71 3.7
Table 1: continued
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 336.983–0.183 16 36 12.38 –47 37 59.1 –76 –77,–74 0.4 45 –78,45 0.18 omc
G 336.991–0.024 16 35 32.53 –47 31 12.4 –48 –61,–44 4 –49 –54,–44 1.0 c
G 336.994–0.027 16 35 34.01 –47 31 12.2 –121 –137,–80 160 –120 –177,–47 158 omg
G 336.995–0.024 16 35 33.53 –47 31 00.6 0.2 –54 –54,–48 1.1 g
G 337.258–0.101 16 36 56.36 –47 22 27.5 –69 –71,–52 1.6 –69 –69,–68 0.33 omg
G 337.404–0.402 16 38 50.57 –47 28 00.8 –40 –53,–37 140 –40 –49,–35 137 omcg
G 337.612–0.060 16 38 09.46 –47 05 00.3 –52 –101,–47 38 –51 –99,–46 17 omg
G 337.687+0.137 16 37 35.60 –46 53 46.3 –74 –151,–73 0.6 mg
G 337.705–0.053 16 38 29.72 –47 00 35.7 –48 –147,5 54 –49 –159,–31 39 omcg
G 337.916–0.477 16 41 10.49 –47 08 02.9 –46 –80,–28 400 –33 –65,–27 321 o
G 337.920–0.456 16 41 06.14 –47 07 02.3 –40 –42,–39 50 –40 –69,–27 22 om
G 337.994+0.133 16 38 48.63 –46 40 15.7 –114 –117,–110 4.5 –113 –116,–111 4.5
G 337.998+0.137 16 38 48.53 –46 39 56.4 –39 –50,–32 30 –38 –47,–30 27 omg
G 338.069+0.011 16 39 37.98 –46 41 44.9 –37 –40,–21 1.3 –28 –46,–22 3.9 g
G 338.075+0.012 16 39 38.88 –46 41 26.8 –50 –51,–50 0.5 0.2 omc
G 338.075+0.010 16 39 39.78 –46 41 31.8 –132 –139,–21 1.2 –48 –51,–28 1.2 m
G 338.077+0.019 16 39 37.69 –46 41 05.6 –40 –41,–38 1.0 –40 –40,–39 1.3 g
G 338.281+0.542 16 38 09.16 –46 11 02.6 –61 –68,–59 12 –64 –67,–58 4.6 omg
G 338.427+0.051 16 40 50.25 –46 24 05.5 –30 –46,–29 0.48
G 338.430+0.053 16 40 50.50 –46 23 53.0 –44 –51,–29 3.2 g
G 338.433+0.057 16 40 50.08 –46 23 33.8 –29 –30,–29 0.19 m
G 338.435+0.055 16 40 51.23 –46 23 34.5 –31 –31,–30 0.58
G 338.436+0.057 16 40 51.05 –46 23 26.8 –35 –56,–34 0.30
G 338.440+0.064 16 40 49.87 –46 22 59.5 –81 –81,–80 0.6 g
G 338.461–0.245 16 42 15.57 –46 34 18.6 –53 –119,–51 9 –52 –114,–49 8 omg
G 338.462–0.259 16 42 19.49 –46 34 48.3 0.2 –54 –55,–53 0.35
G 338.472+0.289 16 39 58.99 –46 12 36.2 –54 –62,–22 25 –29 –62,–25 10 omg
G 338.562+0.217 16 40 38.12 –46 11 24.8 –39 –40,–39 0.22 mg
G 338.567+0.110 16 41 07.16 –46 15 28.1 –76 –92,–74 3.2 m
G 338.682–0.084 16 42 24.12 –46 17 59.1 –6 –18,–5 2.2 –16 –18,–6 0.7 ocg
G 338.920+0.550 16 40 34.02 –45 42 07.9 –110 –125,–65 17 –68 –127,–64 5.3 mg
G 338.925+0.556 16 40 33.63 –45 41 37.9 –63 –85,–61 160 –62 –86,–6 116 om
G 338.924–0.060 16 43 13.25 –46 06 04.2 –64 –69,–63 2.3
G 339.582–0.127 16 45 58.88 –45 38 47.4 –28 –32,–26 0.27 mg
G 339.584–0.128 16 45 59.63 –45 38 44.3 –40 –41,–26 1.8 g
G 339.585–0.126 16 45 59.18 –45 38 36.7 –41 –75,–39 0.40 g
G 339.586–0.128 16 45 59.92 –45 38 39.7 –106 –112,–105 0.5 g
G 339.609–0.115 16 46 01.57 –45 37 07.3 0.2 –71 –82,–67 3.0
G 339.622–0.121 16 46 06.03 –45 36 44.5 –34 –38,–32 90 –33 –36,–32 43 om
G 339.762+0.055 16 45 51.56 –45 23 31.0 –57 –58,–57 0.25 mg
G 339.884–1.259 16 52 04.71 –46 08 33.6 –32 –50,–28 50 –51 –52,–24 4.3 om
G 340.054–0.243 16 48 13.82 –45 21 43.9 –54 –58,–44 35 omg
G 340.785–0.096 16 50 14.84 –44 42 24.7 –120 –121,–111 1.0 0.2 omg
G 341.218–0.212 16 52 17.92 –44 26 51.6 –43 –47,–38 120 –39 –49,–23 33 omg
G 341.276+0.062 16 51 19.50 –44 13 44.0 –77 –80,–58 5 –64 –83,–62 10 omg
G 342.484+0.183 16 55 02.39 –43 12 59.3 –43 –44,–36 0.6 mg
G 343.126–0.065 16 58 17.54 –42 52 15.8 –16 –17,–15 2.5 –21 –23,–20 8
G 343.127–0.063 16 58 17.29 –42 52 06.6 –35 –45,–20 250 –30 –46,–16 208 o
G 344.226–0.576 17 04 09.36 –42 18 58.0 0.2 –19 –19,–18 0.33
G 344.228–0.569 17 04 07.85 –42 18 38.9 –24 –28,31 8 –25 –52,–9 1.4 omg
G 344.421+0.046 17 02 08.53 –41 46 56.4 –27 –32,–18 1.8 –26 –31,–24 0.9
G 344.582–0.024 17 02 57.94 –41 41 54.1 –4 –20,5 250 –4 –52,6 127 omcg
G 345.004–0.224 17 05 11.12 –41 29 04.1 –23 –46,16 3.0 15 –89,15 3.7 omcg
G 345.010+1.793 16 56 47.51 –40 14 23.9 –17 –19,10 2.0 0.2 omc
G 345.010+1.802 16 56 45.41 –40 14 04.2 –28 –33,–26 7 –25 –31,–18 23
G 345.012+1.797 16 56 47.01 –40 14 08.5 –12 –13,7 50 –12 –12,7 29 m
G 345.397–0.950 17 09 33.08 –41 36 20.4 –21 –22,–20 3.1 –21 –27,–20 6
G 345.402–0.948 17 09 33.62 –41 36 02.9 –26 –32,–21 8 –23 –32,–21 2.9
G 345.405–0.947 17 09 33.83 –41 35 50.8 0.5 –28 –28,–23 0.5
G 345.406–0.942 17 09 32.71 –41 35 37.6 –15 –19,–12 3.0 –18 –20,–17 1.9
Table 1: continued
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 345.408–0.953 17 09 35.85 –41 35 56.5 0.5 –15 –16,36 0.5 omc
G 345.412–0.955 17 09 37.08 –41 35 48.9 0.2 –55 –55,–54 1.6
G 345.425–0.951 17 09 38.64 –41 35 03.3 –13 –15,–12 1.5 –13 –16,–13 1.1 m
G 345.438–0.074 17 05 56.75 –41 02 54.9 –11 –32,–9 40 –12 –37,–8 15 o
G 345.482+0.309 17 04 28.41 –40 46 52.1 –52 –80,–24 15 –55 –82,–51 1.8
G 345.487+0.314 17 04 28.19 –40 46 28.6 –16 –24,2 6 –13 –39,–12 0.7 m
G 345.493+1.469 16 59 41.47 –40 03 46.2 5 3,6 6 0.2 o
G 345.494+1.470 16 59 41.15 –40 03 39.9 1 –16,2 1.0 0 –18,–4 1.8
G 345.495+1.473 16 59 40.78 –40 03 28.9 –60 –62,–16 4.0 –9 –10,–8 1.5
G 345.505+0.348 17 04 23.02 –40 44 23.5 –3 –43,1 22 –4 –42,4 4.5 om
G 345.505+0.343 17 04 24.35 –40 44 32.1 0.2 –68 –70,–67 0.8
G 345.699–0.090 17 06 50.72 –40 50 58.9 –10 –87,102 200 –5 –92,141 216 og
G 346.480+0.132 17 08 22.67 –40 05 26.9 –10 –12,–8 1.2 0.2 omg
G 346.522+0.085 17 08 42.35 –40 05 08.1 4 –2,14 2.9 m
G 346.529+0.106 17 08 38.12 –40 04 03.9 4 –1,5 1.6
G 347.588+0.213 17 11 27.61 –39 09 08.1 –93 –94,–93 0.7
G 347.623+0.148 17 11 50.09 –39 09 45.8 –118 –120,–117 0.5 –118 –122,–116 1.0
G 347.628+0.149 17 11 50.85 –39 09 29.6 –125 –133,–122 0.5 0.2 omg
G 347.632+0.210 17 11 36.30 –39 07 06.5 –88 –95,–24 6 mc
G 348.533–0.974 17 19 16.20 –39 04 30.6 –56 –59,–10 3.2 –31 –93,24 1.8
G 348.534–0.983 17 19 18.64 –39 04 47.3 –21 –30,–11 2.2 –14 –109,–12 0.9
G 348.551–0.979 17 19 20.61 –39 03 49.2 –30 –32,–15 1.4 –18 –18,–17 0.28 mg
G 348.726–1.038 17 20 06.42 –38 57 13.2 –11 –64,42 115 –10 –77,61 162
G 348.885+0.096 17 15 50.25 –38 10 12.3 –81 –84,–77 8 –80 –87,–77 8 omg
G 348.892–0.180 17 17 00.26 –38 19 27.9 7 6,12 2.0 omg
G 349.052+0.002 17 16 43.25 –38 05 18.2 15 14,17 3.0 0.2
G 349.067–0.018 17 16 50.82 –38 05 13.8 5 3,7 1.6 13 –14,19 1.0 omg
G 349.074–0.015 17 16 51.23 –38 04 49.3 –27 –32,–20 1.6 –26 –32,–24 1.2 g
G 349.068+0.110 17 16 19.24 –38 00 48.3 –25 –32,–22 3.0 –21 –22,–20 1.4
G 349.092+0.105 17 16 24.66 –37 59 45.4 –80 –84,–74 43 –80 –84,–72 154 omg
G 350.015+0.433 17 17 45.43 –37 03 12.9 –35 –50,–26 4.7 omg
G 350.098+0.099 17 19 21.82 –37 10 41.2 –44 –45,–42 1.8 0.2
G 350.098+0.080 17 19 26.67 –37 11 20.8 –66 –68,–65 6 –67 –69,–67 2.6 g
G 350.100+0.081 17 19 26.74 –37 11 09.8 –68 –69,–67 4.0 –68 –69,–63 5
G 350.105+0.084 17 19 26.78 –37 10 51.5 –71 –102,–38 6 –71 –74,–29 14 m
G 350.110+0.087 17 19 26.96 –37 10 29.0 –72 –74,–71 8 –72 –73,–70 14 g
G 350.112+0.089 17 19 26.96 –37 10 19.9 –172 –175,–110 2.0 –128 –164,–106 2.9
G 350.113+0.095 17 19 25.69 –37 10 04.8 –66 –70,–64 2.5 –64 –79,–63 1.4 og
G 350.274+0.120 17 19 47.07 –37 01 16.6 –63 –63,–61 2.9
G 350.299+0.122 17 19 50.89 –37 00 00.6 –68 –68,–67 0.17 m
G 350.330+0.100 17 20 01.79 –36 59 14.3 –68 –69,–60 1.0 –62 –68,–48 1.9 o
G 350.341+0.140 17 19 53.60 –36 57 19.0 –105 –105,–58 3.2 g
G 350.686–0.491 17 23 28.71 –37 01 47.9 –23 –22,–24 0.6 –14 –14,–13 1.0 omg
G 350.690–0.490 17 23 29.19 –37 01 35.6 0.6 –22 –24,–21 3.4
G 351.160+0.696 17 19 57.50 –35 57 54.1 –3 –11.5,–0.5 9 –3 –10,2 18 omc
G 351.163+0.696 17 19 58.13 –35 57 48.9 t –10 –13,–9 10
G 351.240+0.668 17 20 17.98 –35 54 57.6 –24 –38,31 21
G 351.243+0.671 17 20 17.76 –35 54 42.8 –77 –108,84 453 m
G 351.246+0.668 17 20 19.01 –35 54 38.2 21 19,22 1.3 c
G 351.417+0.646 17 20 53.29 –35 46 58.3 –10 –58,50 1400 om
G 351.582–0.353 17 25 25.35 –36 12 44.0 –89 –120,–87 1600 omg
G 351.775–0.536 17 26 42.50 –36 09 15.9 –2 –32,21 85 om
G 352.098+0.160 17 24 45.25 –35 29 48.8 –75 –75,–73 2.5 g
G 352.111+0.176 17 24 43.79 –35 28 37.7 –60 –61,–60 1.3 mg
G 352.133–0.944 17 29 22.46 –36 04 59.9 –11 –17,–6 27 mg
G 352.162+0.199 17 24 46.36 –35 25 19.9 –45 –46,–44 1 –45 –119,–43 0.28 og
G 352.517–0.155 17 27 11.34 –35 19 32.0 –49 –53,–46 12 om
G 352.525–0.158 17 27 13.44 –35 19 15.7 –51 –53,–49 3.6 mg
G 352.623–1.076 17 31 14.93 –35 44 47.5 2 0,2 28 2 –7,3 8
G 352.630–1.067 17 31 13.94 –35 44 08.8 –2 –10,20 35 0 –13,18 700 om
Table 1: continued
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 353.273+0.641 17 26 01.57 –34 15 14.7 –49 –110,–5 366 m
G 353.408–0.350 17 30 23.38 –34 41 29.8 0.2 –14 –15,–13 0.6 g
G 353.411–0.356 17 30 25.31 –34 41 35.0 0.2 –20 –21,–17 6.4
G 353.411–0.362 17 30 26.78 –34 41 46.6 0.2 –7 –7,–5 1.8 c
G 353.413–0.367 17 30 28.47 –34 41 49.1 –17 –29,–8 2.0 –20 –26,–9 7 g
G 353.413–0.365 17 30 27.84 –34 41 44.6 –20 –24,–18 4.5 –19 –25,–18 2.2
G 353.414–0.363 17 30 27.56 –34 41 38.9 –10 –11,–9 2 1 –22,7 1.7
G 353.463+0.563 17 26 51.25 –34 08 25.3 –47 –52,–46 1 g
G 353.464+0.562 17 26 51.61 –34 08 24.1 –60 –61,–59 0.7 omg
G 354.594+0.469 17 30 14.47 –33 15 03.2 –22 –25,–20 9 0.2
G 354.615+0.472 17 30 17.22 –33 13 54.4 –38 –40,–12 1.6 0.2 om
G 354.703+0.297 17 31 12.96 –33 15 17.6 0.4 105 104,112 1.6
G 354.712+0.293 17 31 15.38 –33 14 57.8 96 95,105 1.1 0.2 g
G 354.722+0.302 17 31 14.87 –33 14 08.3 0.2 99 96,101 0.38
G 355.343+0.147 17 33 29.00 –32 48 00.1 17 9,35 34 om
G 355.345+0.149 17 33 28.83 –32 47 49.9 72 8,109 2.2 m
G 357.965–0.164 17 41 20.12 –30 45 15.9 –4 –5,–3 53 –19 –20,–19 0.9 mg
G 357.967–0.163 17 41 20.30 –30 45 07.0 0 –80,100 40 –65 –81,87 57 om
G 358.371–0.468 17 43 32.01 –30 34 11.4 10 –5,12 2.7 2 2,31 1.4 mg
G 358.386–0.483 17 43 37.72 –30 33 50.6 –1 –4,1 4.5 0 –3,1 3.6 omcg
G 359.137+0.032 17 43 25.61 –29 39 18.6 –1 –117,26 300 omg
G 359.419–0.104 17 44 38.27 –29 29 12.0 0.2 –26 –59,2 1.0
G 359.436–0.102 17 44 40.23 –29 28 12.2 –59 –61,–50 15 –59 –61,–54 9 mg
G 359.436–0.104 17 44 40.66 –29 28 16.1 –56 –57,–55 1.5 –47 –48,–47 0.37 om
G 359.441–0.111 17 44 42.87 –29 28 15.4 –65 –66,–64 1.8 0.2
G 359.442–0.106 17 44 42.00 –29 28 00.6 –53 –54,–52 9 –53 –56,–52 0.928 g
G 359.442–0.104 17 44 41.47 –29 27 58.8 t –60 –62,–58 0.8
G 359.443–0.104 17 44 41.82 –29 27 56.5 t –49 –52,–48 0.6 g
G 359.615–0.243 17 45 39.12 –29 23 29.6 22 –16,73 7 64 –15,68 14 omg
G 359.969–0.457 17 47 20.08 –29 11 59.0 11 10,16 27 om
G 0.209–0.002 17 46 07.44 –28 45 32.1 39 18,42 2.2 c
G 0.212–0.002 17 46 07.86 –28 45 23.0 56 55,65 0.9 m
G 0.216–0.023 17 46 13.20 –28 45 49.8 –11 –16,8 1.7 g
G 0.308–0.177 17 47 02.38 –28 45 55.2 –26 –27,–26 1.8 g
G 0.316–0.201 17 47 09.29 –28 46 15.5 23 14,31 22 mg
G 0.376+0.040 17 46 21.29 –28 35 39.7 40 5,58 55 omg
G 0.497+0.188 17 46 03.96 –28 24 50.7 –8 –72,25 7 26 –50,34 2.5 omg
G 0.547–0.851 17 50 14.52 –28 54 28.8 20 –60,110 200 omg
G 0.655–0.045 17 47 20.88 –28 23 59.9 –52 –55,–50 4.0
G 0.657–0.042 17 47 20.44 –28 23 46.4 62 60,64 70 og
G 0.665–0.032 17 47 19.07 –28 23 03.5 4 0,7 4.3 g
G 0.668–0.035 17 47 20.26 –28 23 02.6 59 50,90 408 og
G 0.677–0.028 17 47 19.64 –28 22 18.9 36 14,132 330 g
G 2.143+0.009 17 50 36.13 –27 05 46.4 37 35,70 0.6 omg
G 2.536+0.198 17 50 46.66 –26 39 44.9 25 –1,63 30 m
G 5.886–0.392 18 00 30.52 –24 03 58.2 11 –10,23 40 om
G 5.897–0.445 18 00 43.90 –24 04 58.1 19 19,20 0.9
G 5.901–0.430 18 00 40.95 –24 04 19.6 14 –40,30 3.9 m
G 5.913–0.388 18 00 33.12 –24 02 28.4 –50 –65,–47 9.2 g
G 6.049–1.447 18 04 53.19 –24 26 40.3 20 18,22 1.0 o
G 6.534–0.105 18 00 49.44 –23 21 40.2 22 6,23 0.5 g
G 6.611–0.082 18 00 54.15 –23 17 00.8 6 –34,11 7 mg
G 6.796–0.257 18 01 57.71 –23 12 32.5 14 10,20 10 1 –1,24 5 omg
G 8.139+0.226 18 03 00.83 –21 48 09.5 16 1,24 18 mg
G 8.670–0.356 18 06 19.17 –21 37 31.0 34 30,44 10 36 –9,43 3.4 omc
G 8.673–0.354 18 06 18.98 –21 37 17.9 –4 –23,–3 0.5 –8 –20,4 0.36
G 9.620+0.194 18 06 14.97 –20 31 37.5 5 –30,50 25 6 –19,11 12 o
G 9.622+0.195 18 06 14.88 –20 31 31.0 21 0,22 1.4 22 0,23 1.3 om
G 9.986–0.028 18 07 50.20 –20 18 55.9 49 44,60 4.0 mg
G 10.288–0.125 18 08 49.44 –20 05 57.4 9 9,11 0.5 m
Table 1: continued
Water maser RA Dec Vpeak Vrange Speak Vpeak Vrange Speak Associations
() (J2000) (J2000) () () (Jy) () () (Jy)
(degrees) (h m s) ( ) 2003 2003 2003 2004 2004 2004
G 10.307–0.270 18 09 24.29 –20 09 08.8 33 32,33 0.8
G 10.323–0.160 18 09 01.57 –20 05 07.6 –3 –6,62 3.2 m
G 10.331–0.159 18 09 02.30 –20 04 40.2 11 7,22 1.0
G 10.342–0.143 18 09 00.11 –20 03 35.8 8 –40,61 4.8 mg
G 10.445–0.018 18 08 45.01 –19 54 35.1 71 58,85 6 70 69,81 2.7
G 10.473+0.027 18 08 38.30 –19 51 48.8 60 30,93 45 62 28,129 169 omcg
G 10.480+0.034 18 08 37.69 –19 51 12.4 64 63,65 12 0.2 om
G 10.623–0.383 18 10 28.57 –19 55 49.4 2 –11,5 350 og
G 10.625–0.335 18 10 18.07 –19 54 20.5 –5 –6,–5 0.40
G 10.959+0.022 18 09 39.38 –19 26 27.0 25 7,26 2.9 mcg
G 11.034+0.062 18 09 39.75 –19 21 21.1 18 16,19 0.6 om
G 11.498–1.486 18 16 22.32 –19 41 26.1 17 –3,21 112 m
G 11.903–0.142 18 12 11.41 –18 41 33.0 36 35,38 0.3 0.2 om
G 12.203–0.107 18 12 40.25 –18 24 47.4 33 32,35 6 35 32,37 8 m
G 12.209–0.102 18 12 39.88 –18 24 17.1 21 –12,42 141 22 –15,50 51 mcg
G 12.216–0.119 18 12 44.55 –18 24 25.2 26 25,42 6 26 0,38 10 og
G 12.681–0.183 18 13 54.82 –18 01 47.0 61 55,63 1200 61 17,62 445 omg
G 12.884+0.502 18 11 47.92 –17 31 21.3 42 41,43 1.3 40 34,41 1.1
G 12.889+0.489 18 11 51.54 –17 31 27.9 30 28,32 45 30 28,39 59 omg
G 12.901–0.242 18 14 34.50 –17 51 51.6 35 23,37 8 36 23,37 12 g
G 12.908–0.260 18 14 39.45 –17 52 01.4 37 21,39 0.8 0.2 om
G 15.016–0.679 18 20 23.11 –16 12 38.8 t 19 14,21 11
G 15.025–0.658 18 20 19.50 –16 11 31.9 t 25 14,31 4.2
G 15.026–0.654 18 20 18.72 –16 11 23.3 27 27,31 29 28 26,31 16
G 15.028–0.673 18 20 23.04 –16 11 48.4 19 17,28 197 20 14,31 67
G 15.032–0.667 18 20 22.35 –16 11 27.2 45 44,46 1.8 40 –8,41 1.1 g
G 15.032–0.670 18 20 23.01 –16 11 30.1 t 26 14,28 12
G 15.034–0.667 18 20 22.58 –16 11 18.4 t 17 17,21 3.8
G 17.638+0.156 18 22 26.45 –13 30 12.4 27 15,29 230 27 17,35 245 om
Table 1: continued

3 Results

The search for 22-GHz water masers carried out with the ATCA in 2003 October and 2004 July towards 202 OH maser sites and 104 methanol maser sites (with no reported OH maser emission) resulted in the detection of 379 distinct water maser sites (Table LABEL:tab:masers). Spectra of all detected sources are shown in Fig. 1. For the majority of sources, the spectra are taken from the 2004 data, except where sources were either not observed or not detected at this epoch. For these latter cases we show the 2003 spectra and distinguish them from the 2004 spectra with a ‘2003’ in the top left hand corner of each spectrum. The 2003 spectra were obtained directly from the uv data with a phase shift to the source position, and amplitude correction for offset from the field centre. For eight sources we show a spectrum from each epoch to either highlight that a weak source is a genuine detection (333.387+0.032 and 336.983-0.183) or to give an indication of the level of variability seen over the 10 month time-scale (284.350–0.418, 321.148–0.529, 327.291–0.578, 345.004–0.224, 15.026–0.654 and 15.028–0.673). A velocity range of 200  is shown for the majority of sources, but there are several instances where we either decreased this value to clearly show individual features in spectra that are complex (or include multiple nearby sources) or increased it in order to display extremely high velocity features. A decreased velocity range of 100  is shown for the following sources; 301.136–0.225, 301.136–0.226a, 301.136–0.226b, 301.137–0.225, 335.060–0.428/335.059–0.428, 336.991–0.024, 336.995–0.024, 359.441–0.111, 359.442–0.106, 359.442–0.104, 359.443–0.104. An increased range of 300  was used for 320.120–0.440, 330.954–0.182, 333.219–0.062, 333.234–0.060, 345.699–0.090, 357.965–0.164, 357.967–0.163, 0.547–0.851, 0.668–0.035, 0.665–0.032, 0.655–0.045, 0.657–0.042 and 0.677–0.028.

A number of the sources that we detect have been observed previously and have been presented in the literature (e.g. Johnston et al., 1972; Caswell et al., 1974; Kaufmann et al., 1976; Genzel & Downes, 1977; Batchelor et al., 1980; Braz & Scalise, 1982; Braz & Epchtein, 1983; Caswell et al., 1989; Hofner & Churchwell, 1996, and references therein) but the majority of these earlier observations (performed up to 20 years ago) were made with relatively poor positional accuracy. Due to the intrinsically variable nature of water masers, many sources exhibit levels of variability so extreme that they display no common spectral features at epochs separated by many years. This, combined with the tendency of water masers to form in clusters, and the previously poor positional information, mean that it is almost impossible to accurately match up sources from the literature with our present data. We have therefore limited our references (in Section  4) to previous detections of sources that were observed with high positional precision (e.g. Forster & Caswell, 1989; Breen et al., 2007; Caswell & Phillips, 2008), or where there was little doubt that the sources were the same.

The majority of OH maser targets were observed in both 2003 and 2004, whereas the methanol maser targets were observed in 2004 only. Where appropriate data were available for both epochs, reported positions are the average of the two since, in general, it provides the most accurate positions for the sources. For sources north of declination –20, we have used a weighting of 2:1 for the declinations in favour of the 2004 data to account for the three times more elongated beam of the 2003 observations (a consequence of the different array configurations). Sources that were observed at both epochs allowed a direct comparison of the positions for each of the sources and therefore afford verification of the positional uncertainties.

Additional to direct comparison of 2003 with 2004 data, an overall assessment of data quality and reliability was made in several other ways. FC89 and FC99 used their VLA observations of a sample of more than 70 SFR targets with OH and water masers, to show that more than half were a simple association of water and OH masers coincident to within their combined relative errors (of typically 1 arcsec). Subsequent observation of the more southerly OH masers in that sample with the ATCA (C98) showed that the most southerly ones (observed by the VLA inevitably at low elevation) had significantly larger position uncertainties, and corrections to the positions resulted in an increased number of close OH/water maser associations. Thus we may expect the majority of our sample to show a water maser position coincident with OH, and thus the OH position is an indirect check on the accuracy of the newly derived water positions.

A further assessment was made using the 35 masers north of declination –47 degrees which are present in the FC89 target list. The FC89 absolute positions for the more southerly targets, although of variable quality for the OH masers (where ionospheric effects at low elevation can be significant), appear to remain excellent for the water masers. Thus we can directly compare our positions to those of FC89, to assess the errors in our current data. Furthermore, in some fields there is a strong ultracompact Hii (UCHii) region that has been measured to subarcsecond accuracy, such as in the 6-GHz observations of C97 and C2001; where these are detectable in the current 22-GHz observations, they allow a further check on the positions, without the need for any assumptions concerning the true relative positions of the masers.

From these many comparisons, we are able to estimate our rms positional uncertainty as 2 arcsec. The target OH and methanol masers have rms position uncertainties of 0.4 arcsec (C98, Caswell 2009). An additional positional uncertainty in characterising any water maser site by a single position arises because a single site sometimes consists of many separate spots with angular separations as extensive as 4 arcsec (e.g. Reid et al., 1988), explicable by an outflow (e.g. Caswell & Phillips, 2008). We therefore regard our water maser sources to be associated with OH or methanol masers when they are separated by less than 3 arcsec, a threshold which captures most associations without diluting them with too many false, chance, coincidences; see also further discussion in Section 5.2. Where the water maser positions are derived from a single epoch, we relax this threshold to 4.5 arcsec. As the positions of the 22-GHz radio continuum have also been determined from a single epoch, a threshold of 4.5 arcsec is similarly adopted for continuum associations. Most of our proposed associations correspond to a much better accuracy (see Table 3) than our thresholds. There are, however, some more complex cases that have been judged on individual merit as discussed in detailed considerations summarized in Section 4. For example, the required precision of agreement was relaxed for sources believed to be nearby, at a distance of less than 2 kpc. Comparison of our 379 water maser positions with the positions of OH and methanol masers shows that 128 are coincident with both species, 33 are coincident with OH only and 70 are coincident with the location of methanol masers (see Section 5.3 for more extensive discussion). Surprisingly, 148 sources have no association with other maser species and we describe these as ‘solitary’.

Details for the 379 sources that we detect are presented in Table LABEL:tab:masers and, following the usual practice, the Galactic longitude and latitude of each source, listed in the first column, is used as an identifying source name for each water maser. These Galactic coordinates are derived from the more precise measurements of equatorial coordinates given in columns 2 and 3. The peak velocity and velocity range (w.r.t. lsr), followed by the peak flux density, are given in columns 4, 5 and 6 for the 2003 epoch and in columns 7, 8 and 9 for the 2004 epoch. The presence of a ‘–’ in either column 6 or 9 indicates that no observations were made for that source during the 2003 or 2004 observations respectively and a ‘t’ in either column indicates that there is a comment in the text of Section 4 explaining the nature of the detection status at the indicated epoch. The presence of a number preceded by a ’’ in either column 6 or 9 indicates that no emission above the quoted flux density was detected at that epoch. Column 10 gives a list of associations for each water maser source; here, the presence of an ‘o’ denotes the presence of an associated OH maser, ‘m’ the presence of an associated methanol maser, ‘c’ the presence of associated 22-GHz continuum emission (in our observations) and ‘g’ the presence of an associated GLIMPSE point source. A ’’ in this column indicates that the source is outside the GLIMPSE survey region. A ’’ following an ‘o’ indicates that the OH maser is strictly outside our association threshold but is associated with the methanol maser that falls within our threshold for a given source, meaning that either all three sources are coincident or the water maser is offset; similarly for the case where a ’’ follows an ‘m’. In some cases we have the situation that both the OH and the methanol masers are strictly located outside the association threshold but we regard them as associated through special circumstances, in which case we have used the ’’ after both the ‘o’ and the ‘m’. In the case of 301.136-0.226 a second water maser site lies within the association threshold for the same methanol and OH masers and the association is shown in parentheses.

OH masers that were searched and resulted in no water maser detection are listed in Table 2. The first column gives the name of the OH maser followed by its right ascension and declination. Column 4 gives the angular separation between the OH maser and the nearest methanol maser (Caswell, 2009) within 2.5 arcsec, and when a ‘–’ is present, this signifies that there is no methanol maser within 2.5 arcsec of the OH maser.

An extensive list of the OH and methanol masers associated with our water maser sources, as well as water maser associations with 22-GHz continuum sources is given in Table 3. All OH and methanol masers as well as 22-GHz radio continuum that fall within 5 arcsec of the water masers are presented. Column 1 in Table 3 gives the water maser source name, and the name of the nearby OH and methanol masers are given in columns 2 and 4 respectively. The source names, based on the precise positions of individual species, inevitably differ slightly in a few cases due to different small position errors. The angular separations between the water masers and OH masers are given in column 3, and between water and methanol masers in column 5. Columns 6, 7 and 8 give the peak velocity of the water (2004 values are given unless not available, in which case the 2003 value is used) and the coincident OH and methanol maser sources. Column 9 gives the Galactic coordinates of 22-GHz continuum sources that we detect, followed by the angular separation between the continuum source and the water maser in column 10. The discussion of individual sources in Section 4 includes some comparisons between the positions of water maser sources and other masers, continuum and GLIMPSE sources.

A complete list of the continuum sources detected towards water maser sources in the 2004 observations is given in Table 4. Associations between the 29 water maser sources observed only during the 2003 observations and possibly associated 22-GHz continuum sources (see Section 5.6) have not been determined.

OH maser RA Dec Methanol
() (J2000) (J2000) maser
degrees (h m s) ( ) sep. (arcsec)
G 232.621+0.996 07 32 09.82 –16 58 13.0 0.7
G 300.969+1.147 12 34 53.24 –61 39 40.3 0.5
G 305.200+0.019 13 11 16.90 –62 45 54.7 0.5
G 305.202+0.208 13 11 10.61 –62 34 37.8 1.3
G 306.322–0.334 13 21 23.00 –63 00 30.4 0.9
G 309.921+0.479 13 50 41.73 –61 35 09.8 0.9
G 313.705–0.190 14 22 34.72 –61 08 27.4 0.8
G 316.359–0.362 14 43 11.00 –60 17 15.3 2.5
G 321.030–0.485 15 15 51.67 –58 11 18.0 0.9
G 323.459–0.079 15 29 19.36 –56 31 21.4 1.4
G 328.307+0.430 15 54 06.48 –53 11 40.3
G 329.339+0.148 16 00 33.15 –52 44 39.8 0.2
G 331.542–0.066 16 12 09.05 –51 25 47.2 0.5
G 331.543–0.066 16 12 09.16 –51 25 45.3 0.2
G 331.556–0.121 16 12 27.19 –51 27 38.1 0.2
G 332.295+2.280 16 05 41.72 –49 11 30.5 0.2
G 332.824–0.548 16 20 10.23 –50 53 18.1
G 333.135–0.431 16 21 02.97 –50 35 10.1 2.4
G 335.556–0.307 16 30 56.00 –48 45 51.0 0.8
G 336.822+0.028 16 34 38.26 –47 36 33.0 0.8
G 336.941–0.156 16 35 55.22 –47 38 45.7 0.4
G 338.875–0.084 16 43 08.23 –46 09 12.8 0.2
G 339.053–0.315 16 44 49.16 –46 10 14.4 2.2
G 339.282+0.136 16 43 43.12 –45 42 08.4 0.4
G 339.682–1.207 16 51 06.21 –46 15 57.8 0.4
G 343.930+0.125 17 00 10.92 –42 07 18.7 0.6
G 344.419+0.044 17 02 08.67 –41 47 08.6 1.8
G 345.498+1.467 16 59 42.81 –40 03 36.2 0.4
G 347.870+0.014 17 13 08.80 –39 02 29.5
G 348.550–0.979 17 19 20.39 –39 03 51.8 0.3
G 348.579–0.920 17 19 10.56 –39 00 24.5 0.6
G 348.698–1.027 17 19 58.91 –38 58 14.1
G 348.703–1.043 17 20 03.96 –38 58 31.3 1.2
G 348.727–1.037 17 20 06.55 –38 57 08.2 0.9
G 350.011–1.342 17 25 06.50 –38 04 00.7 0.5
G 353.410–0.360 17 30 26.20 –34 41 45.5 0.3
G 354.724+0.300 17 31 15.52 –33 14 05.3 0.5
G 356.662–0.264 17 38 29.22 –31 54 40.6 2.0
G 3.910+0.001 17 54 38.77 –25 34 45.2 0.5
G 8.683–0.368 18 06 23.46 –21 37 10.2 0.4
G 12.025-0.031 18 12 01.88 –18 31 55.6 0.3
G 15.034–0.677 18 20 24.75 –16 11 34.9 0.6
Table 2: OH masers with no associated water maser emission. Listed in column 1 is the OH maser source name followed in columns 2 and 3 by the right ascension and declination. Column 4 shows the angular separation between the listed OH maser and a nearby methanol maser; a – in this column indicates that there is no known methanol maser sources within 2.5 arcsec.
Figure 1: Spectra of the 22-GHz water masers detected in 2004 towards sites of OH and methanol masers.
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Figure 1: continuued
Water OH Sep. Methanol Sep. Water OH Methanol Continuum Sep.
() () () Vpeak Vpeak Vpeak ()
(degrees) (degrees) (arcsec) (degrees) (arcsec) () () () (degrees) (arcsec)
G 240.316+0.071 G 240.316+0.071 0.7 89 63
G 263.250+0.514 G 263.250+0.514 2.1 G 263.250+0.514 1.5 20 15.3 12.3
G 284.350–0.418 G 284.351–0.418 1.1 7 6
G 285.263–0.050 G 285.263–0.050 2.0 3 6
G 287.371+0.644 G 287.371+0.644 1.6 G 287.371+0.644 1.5 –11 –4 –1.8
G 290.374+1.661 G 290.374+1.661 1.6 G 290.374+1.661 1.0 –12 –23.3 –24.2
G 291.270–0.719 G 291.270–0.719 2.5 –102 –26.5
G 291.274–0.709 G 291.274–0.709 1.3 G 291.274–0.709 0.7 –32 –24.5 –29.6
G 291.579–0.431 G 291.579–0.431 0.6 G 291.579–0.431 0.7 13 13 14.5
G 291.581–0.435 G 291.582–0.435 3.8 26 10.5
G 291.610–0.529 G 291.610–0.529 0.7 12 18 G 291.611–0.529 2.6
G 291.627–0.529 G 291.626–0.531 4.8
G 294.511–1.622 G 294.511–1.621 2.1 G 294.511–1.621 1.8 –12 –12.7 –12.3
G 294.989–1.719 G 294.990–1.719 2.5 –17 –12.3
G 297.660–0.974 G 297.660–0.973 2.0 26 27.6
G 299.013+0.128 G 299.013+0.128 1.2 G 299.013+0.128 1.1 19 20.3 18.4 G 299.012+0.128 3.3
G 300.504–0.176 G 300.504–0.176 0.6 G 300.504–0.176 1.8 11 22.4 7.5
G 301.136–0.226b G 301.136–0.226 2.0 G 301.136–0.226 2.5 –44 –40.2 –39.8 G 301.136–0.226 1.0
G 301.137–0.225 G 301.136–0.226 2.0 G 301.136–0.226 2.0 –35 –40.2 –39.8
G 305.208+0.207 G 305.208+0.206 3.0 G 305.208+0.206 2.7 –42 –38 –38.3
G 305.361+0.150 G 305.362+0.150 2.1 G 305.362+0.150 2.0 –36 –39.5 –36.5
G 305.799–0.245 G 305.799–0.245 3.0 G 305.799–0.245 2.5 –34 –36.7 –39.5
G 307.805–0.456 G 307.805–0.456 1.5 –7 –14.5
G 308.754+0.549 G 308.754+0.549 0.8 G 308.754+0.549 1.4 –48 –43.5 –51.0
G 308.918+0.124 G 308.918+0.123 3.0 G 308.918+0.123 3.6 –61 –54 –54.7
G 309.384–0.135 G 309.384–0.135 1.3 G 309.384–0.135 0.6 –50 –52 –49.6
G 310.144+0.760 G 310.144+0.760 2.2 G 310.144+0.760 1.0 –63 –57 –55.6
G 311.643–0.380 G 311.643–0.380 1.3 G 311.643–0.380 0.4 36 38 32.5 G 311.643–0.380 1.3
G 312.109+0.262 G 312.108+0.262 1.9 –48 –50.0
G 312.596+0.045 G 312.597+0.045 1.6 –59 –60.0
G 312.599+0.046 G 312.598+0.045 2.1 G 312.598+0.045 2.1 –79 –65.2 –67.9
G 313.457+0.193 G 313.458+0.193 2.1
G 313.470+0.191 G 313.469+0.190 0.9 G 313.469+0.190 1.1 –15 –10 –9.4
G 313.578+0.325 G 313.577+0.325 1.0 G 313.577+0.325 1.9 –47 –47 –47.9
G 313.767–0.862 G 313.767–0.863 1.1 G 313.767–0.863 0.9 –54 –53.5 –54.6
G 314.320+0.112 G 314.320+0.112 2.2 G 314.320+0.112 2.3 –45 –45 –43.7
G 316.361–0.363 G 316.359–0.362 3.2 –3 3.5
G 316.412–0.308 G 316.412–0.308 1.5 G 316.412–0.308 2.3 –20 –2 –5.7 G 316.412–0.308 0.7
G 316.640–0.087 G 316.640–0.087 0.7 G 316.640–0.087 0.9 –15 –22 –19.8
G 316.763–0.011 G 316.763–0.012 1.0 –48 –40
G 316.812–0.057 G 316.811–0.057 2.2 G 316.811–0.057 2.5 –46 –43.5 –46.3
G 317.429–0.561 G 317.429–0.561 2.1 25 25.5 G 317.430–0.561 2.6
G 318.044–1.404 G 318.044–1.405 2.0 G 318.043–1.404 1.6 42 45 46.2
G 318.050+0.087 G 318.050+0.087 0.6 G 318.050+0.087 0.4 –48 –53 –46.5
G 318.948–0.196b G 318.948–0.196 0.8 G 318.948–0.196 0.9 –38 –35.5 –34.7
G 319.399–0.012 G 319.398–0.012 1.1 –5 –1 G 319.399–0.012 0.8
G 319.836–0.196 G 319.836–0.196 1.5 G 319.836–0.197 1.6 –11 –10.5 –9.1
G 320.120–0.440 G 320.120–0.440 0.5 –46 –55.5
G 320.232–0.284 G 320.232–0.284 0.4 G 320.231–0.284 0.6 –67 –64 –66.5
G 320.233–0.284 G 320.234–0.283 3.5
G 321.033–0.483 G 321.033–0.483 0.5 –61 –61.6
G 321.148–0.529 G 321.148–0.529 1.1 G 321.148–0.529 1.1 –97 –63 –66.1
G 322.158+0.636 G 322.158+0.636 1.2 G 322.158+0.636 1.2 –76 –61 –63.3
G 323.740–0.263 G 323.740–0.263 1.1 G 323.740–0.263 0.6 –50 –39 –51.1
Table 3: Water maser sources with associated OH and methanol masers as well as 22-GHz continuum emission. Column 1 shows the water maser source name; column 2 gives the source name of the nearest OH maser within 5 arcsec (– if none) of the detected water maser; column 3 gives the angular separation between the water and the OH masers; column 4 gives the source name of the nearest methanol maser within 5 arcsec (– if none) of the detected water maser; column 5 gives the angular separation between the water maser and the methanol maser; columns 6, 7 and 8 give the water maser, OH maser and methanol maser peak velocities; column 9 gives detected UCHii regions with 5 arcsec of the detected water masers (– if none); and column 10 gives the angular separation between the UCHii region and the detected water maser.
Water OH Sep. Methanol Sep. Water OH Methanol Continuum Sep.
() () () Vpeak Vpeak Vpeak ()
(degrees) (degrees) (arcsec) (degrees) (arcsec) () () () (degrees) (arcsec)
G 324.201+0.122 G 324.200+0.121 2.9 –87 –91.5
G 324.716+0.342 G 324.716+0.342 1.7 G 324.716+0.342 1.5 –58 –50 –46
G 326.662+0.521 G 326.662+0.521 2.0 –39 –38.6
G 326.670+0.554 G 326.670+0.554 2.6 –40 –40.8
G 326.780–0.241 G 326.780–0.241 0.9 –66 –65
G 326.859–0.676 G 326.859–0.677 3.4 –103 –58.0
G 327.119+0.511 G 327.120+0.511 2.3 G 327.120+0.511 1.8 –88 –80.5 –87.0
G 327.291–0.578 G 327.291–0.578 1.2 G 327.291–0.578 0.8 –63 –50.5 –36.8
G 327.391+0.200 G 327.392+0.199 1.5 –86 –84.6
G 327.402+0.445 G 327.402+0.444 3.2 G 327.402+0.444 1.6 –81 –77 –82.6 G 327.402+0.445 0.6
G 327.619–0.111 G 327.618–0.111 0.9 –85 –97.6
G 328.236–0.548 G 328.237–0.547 2.9 G 328.237–0.547 2.6 –38 –41 –44.5 G 328.236–0.547 2.1
G 328.254–0.532 G 328.254–0.532 1.5 G 328.254–0.532 0.8 –50 –37 –37.5
G 328.306+0.432 G 328.307+0.431 3.3
G 328.808+0.633 G 328.809+0.633 2.9 G 328.808+0.633 2.4 –46 –43.5 –43.8 G 328.808+0.633 2.0
G 329.029–0.199 G 329.029–0.200 1.9 –38 –38.5
G 329.030–0.205 G 329.029–0.205 1.5 G 329.029–0.205 1.3 –46 –38.5 –37.4
G 329.031–0.198 G 329.031–0.198 1.3 G 329.031–0.198 0.8 –52 –45.5 –45.5
G 329.066–0.307 G 329.066–0.308 1.5 G 329.066–0.308 1.2 –45 –43.5 –43.8
G 329.183–0.313 G 329.183–0.314 2.3 G 329.183–0.314 1.9 –50 –53 –55.7
G 329.405–0.459 G 329.405–0.459 2.0 G 329.405–0.459 1.5 –77 –69.5 –70.5
G 329.407–0.459 G 329.407–0.459 2.1 –74 –66.7
G 329.622+0.138 G 329.622+0.138 1.7 –82 –84.8
G 330.070+1.064 G 330.070+1.064 1.2 –50 –38.8
G 330.879–0.367 G 330.878–0.367a 0.9 G 330.878–0.367 2.6 –60 –61.8 –59.3 G 330.879–0.367 1.7
G 330.878–0.367b 1.2 –65.6
G 330.954–0.182 G 330.954–0.182 1.3 G 330.953–0.182 3.9 –91 –85.5 –87.6 G 330.954–0.182 1.6
G 331.132–0.244 G 331.132–0.244 0.2 G 331.132–0.244 0.3 –99 –88.5 –84.3
G 331.278–0.188 G 331.278–0.188 0.9 G 331.278–0.188 1.1 –90 –89.5 –78.2
G 331.342–0.346 G 331.342–0.346 1.4 G 331.342–0.346 1.6 –62 –67 –67.4
G 331.442–0.187 G 331.442–0.186 0.5 G 331.442–0.187 0.9 –88 –83 –88.4 G 331.443–0.187 3.5
G 331.512–0.103 G 331.512–0.103 1.4 –90 –88.2 G 331.512–0.103 1.0
G 331.555–0.122 G 331.556–0.121 4.5 G 331.556–0.121 4.4 –99 –100 –103.4
G 332.094–0.421 G 332.094–0.421 2.2 –59 –58.6
G 332.296–0.094 G 332.295–0.094 4.4 –50 –47.0
G 332.352–0.117 G 332.352–0.117 0.8 G 332.352–0.117 0.2 –60 –44 –41.8
G 332.604–0.167 G 332.604–0.167 1.6 –46 –50.9
G 332.725–0.621 G 332.726–0.621 1.4 G 332.726–0.621 1.0 –58 –48 –49.6
G 332.826–0.549 G 332.826–0.549 3.0 –59 –61.7 G 332.826–0.549 1.1
G 332.964–0.679 G 332.963–0.679 1.6 –52 –45.8
G 333.030–0.063 G 333.029–0.063 1.3 –40 –55.2 G 333.030–0.063 0.7
G 333.121–0.434 G 333.121–0.434 1.2 –47 –49.3
G 333.126–0.440 G 333.126–0.440 1.0 –52 –43.9
G 333.128–0.440 G 333.128–0.440 2.5 –124 –44.6
G 333.234–0.060 G 333.234–0.060 0.6 –88 –84
G 333.315+0.106 G 333.315+0.105 2.8 G 333.315+0.105 3.0 –48 –47 –45
G 333.387+0.032 G 333.387+0.032 0.6 G 333.387+0.032 1.1 –61 –74 –73.9
G 333.467–0.164 G 333.466–0.164 2.1 G 333.466–0.164 2.5 –42 –43.5 –42.5 G 333.466–0.163 4.7
G 333.608–0.215 G 333.608–0.215 0.2 –49 –51
G 333.646+0.058 G 333.646+0.058 0.9 –89 –87.3
G 333.682–0.436 G 333.683–0.437 1.6 –3 –5.3
G 333.930–0.134 G 333.931–0.135 1.5 –46 –36.7
G 334.635–0.015 G 334.635–0.015 1.0 –26 –30
G 334.935–0.098 G 334.935–0.098 0.4 –17 –19.5
G 335.060–0.428 G 335.060–0.427 1.5 G 335.060–0.427 1.3 –37 –36 –47.0
G 335.585–0.285 G 335.585–0.285 0.5 G 335.585–0.285 0.7 –42 –48 –49.3
G 335.586–0.290 G 335.585–0.289 1.1 G 335.585–0.289 0.8 –56 –53.5 –51.4
G 335.585–0.290 2.3 –47.3
G 335.727+0.191 G 335.726+0.191 2.0 –51 –44.4
G 335.789+0.174 G 335.789+0.174 0.5 G 335.789+0.174 0.9 –46 –51.5 –47.6
Table 3: continued
Water OH Sep. Methanol Sep. Water OH Methanol Continuum Sep.
() () () Vpeak Vpeak Vpeak ()
(degrees) (degrees) (arcsec) (degrees) (arcsec) () () () (degrees) (arcsec)
G 336.018–0.827 G 336.018–0.827 0.6 G 336.018–0.827 0.9 –54 –41.5 –53.4 G 336.018–0.828 0.5
G 336.359–0.137 G 336.358–0.137 3.0 G 336.358–0.137 3.1 –67 –82 –73.6 G3̇36.360–0.137 3.8
G 336.433–0.262 G 336.433–0.262 1.9 –89 –93.3
G 336.830–0.375 G 336.830–0.375 1.6 –20 –22.7
G 336.864+0.005 G 336.864+0.005 1.2 G 336.864+0.005 0.7 –66 –89 –76.1
G 336.983–0.183 G 336.984–0.183 4.2 G 336.983–0.183 3.0 45 –80.5 –80.8 G 336.984–0.184 2.5
G 336.991–0.024 G 336.990–0.025 2.3
G 336.994–0.027 G 336.994–0.027 1.0 G 336.994–0.027 0.6 –120 –123 –125.8
G 337.258–0.101 G 337.258–0.101 0.7 G 337.258–0.101 1.2 –69 –70 –69.3
G 337.404–0.402 G 337.405–0.402 1.5 G 337.404–0.402 0.7 –40 –38 –39.7 G 337.404–0.403 2.0
G 337.612–0.060 G 337.613–0.060 0.6 G 337.613–0.060 0.9 –51 –42 –42
G 337.687+0.137 G 337.686+0.137 2.3 –74 –74.9
G 337.705–0.053 G 337.705–0.053 0.6 G 337.705–0.053 0.9 –49 –49 –54.6 G 337.706–0.054 1.1
G 337.916–0.477 G 337.916–0.477 0.6 –33 –51
G 337.920–0.456 G 337.920–0.456 0.7 G 337.920–0.456 0.9 –40 –39.5 –38.8
G 337.998+0.137 G 337.997+0.136 1.3 G 337.997+0.136 1.1 –38 –35.5 –32.3
G 338.075+0.012 G 338.075+0.012 2.1 G 338.075+0.012 2.3 –50 –47 –53.0 G 338.075+0.012 2.9
G 338.075+0.010 G 338.075+0.009 1.3 –48 –38.2
G 338.281+0.542 G 338.280+0.542 1.2 G 338.280+0.542 1.1 –64 –61 –56.8
G 338.433+0.057 G 338.432+0.058 4.4 –29 –30.2
G 338.461–0.245 G 338.461–0.245 0.4 G 338.461–0.245 0.8 –52 –56 –50.4
G 338.472+0.289 G 338.472+0.289 1.2 G 338.472+0.289 1.1 –29 –32 –30.5
G 338.562+0.217 G 338.561+0.218 2.0 –39 –40.8
G 338.567+0.110 G 338.566+0.110 1.4 –76 –75
G 338.682–0.084 G 338.681–0.084 1.4 –16 –22 G 338.681–0.085 1.5
G 338.920+0.550 G 338.920+0.550 0.8 –68 –61.4
G 338.925+0.556 G 338.925+0.557 0.9 G 338.925+0.557 1.3 –62 –61 –62.3
G 339.582–0.127 G 339.582–0.127 0.6 –28 –31.3
G 339.622–0.121 G 339.622–0.121 0.8 G 339.622–0.121 1.3 –33 –37.3 –32.8
G 339.762+0.055 G 339.762+0.054 1.6 –57 –51
G 339.884–1.259 G 339.884–1.259b 0.7 G 339.884–1.259 0.8 –51 –36 –38.7
G 339.884–1.259a 1.2 –29
G 340.054–0.243 G 340.054–0.244 1.4 G 340.054–0.244 0.8 –54 –53.6 –59.7
G 340.785–0.096 G 340.785–0.096 2.2 G 340.785–0.096 1.6 –120 –102 –105.1
G 341.218–0.212 G 341.218–0.212 1.2 G 341.218–0.212 1.0 –39 –37.3 –37.9
G 341.276+0.062 G 341.276+0.062 0.9 G 341.276+0.062 1.1 –64 –73 –73.8
G 342.484+0.183 G 342.484+0.183 1.1 –43 –41.8
G 343.127–0.063 G 343.127–0.063 2.1 –30 –31.5
G 344.228–0.569 G 344.227–0.569 1.4 G 344.227–0.569 1.0 –25 –30.5 –19.8
G 344.421+0.046 G 344.421+0.045 3.4 –26 –71.5
G 344.582–0.024 G 344.582–0.024 2.2 G 344.581–0.024 2.5 –4 –2.3 1.4 G 344.582–0.024 1.7
G 345.004–0.224 G 345.003–0.224 3.0 G 345.003–0.224 3.1 –26.2 G 345.004–0.225 3.6
G 345.003–0.223 3.3 15 –27 –22.5
G 345.010+1.793 G 345.010+1.793 1.5 G 345.010+1.792 2.1 –17 –22.5 –18 G 345.010+1.792 4.3
G 345.012+1.797 G 345.012+1.797 2.2 –12 –12.7
G 345.408–0.953 G 345.407–0.952 4.6 G 345.407–0.952 4.9 –15 –17.6 –14.4 G 345.408–0.952 3.2
G 345.425–0.951 G 345.424–0.951 1.6 –13 –13.5
G 345.438–0.074 G 345.437–0.074 1.9 –12 –24.3
G 345.487+0.314 G 345.487+0.314 0.6 –13 –22.6
G 345.493+1.469 G 345.494+1.469 3.3 5 –12.7
G 345.505+0.348 G 345.504+0.348 1.8 G 345.505+0.348 2.2 –4 –19.5 –17.7
G 345.699–0.090 G 345.698–0.090 1.2 –5 –6
G 346.480+0.132 G 346.481+0.132 1.5 G 346.481+0.132 1.4 –10 –8 –5.5
G 346.522+0.085 G 346.522+0.085 0.7 4 5.5
G 347.628+0.149 G 347.628+0.148 2.0 G 347.628+0.149 0.9 –125 –94.3 –96.6
G 347.632+0.210 G 347.631+0.211 2.9 –88 –91.9 G 347.632+0.210 0.9
G 348.551–0.979 G 348.550–0.979 3.7 G 348.550–0.979n 1.9 –18 –19.7 –20.0
G 348.550–0.979 3.4 –10
G 348.726–1.038 G 348.727–1.037 4.4 –10 –7.6
G 348.885+0.096 G 348.884+0.096 1.2 G 348.884+0.096 1.4 –80 –73.2 –76.2
Table 3: continued
Water OH Sep. Methanol Sep. Water OH Methanol Continuum Sep.
() () () Vpeak Vpeak Vpeak ()
(degrees) (degrees) (arcsec) (degrees) (arcsec) () () () (degrees) (arcsec)
G 348.892–0.180 G 348.892–0.180 0.6 G 348.892–0.180 1.0 7 9.5 1.4
G 349.067–0.018 G 349.067–0.017 1.1 G 349.067–0.017 1.1 13 15 6.9
G 349.092+0.105 G 349.092+0.106 0.8 G 349.092+0.106 0.9 –80 –80 –80.4
G 349.092+0.105 2.0 –76.5
G 350.015+0.433 G 350.015+0.433 0.1 G 350.015+0.433 1.0 –35 –33 –31.7
G 350.113+0.095 G 350.113+0.095 1.3 –64 –71
G 350.105+0.084 G 350.104+0.084 2.0 –71 –68.4
G 350.105+0.083 3.3 –74.0
G 350.299+0.122 G 350.299+0.122 0.7 –68 –62.1
G 350.330+0.100 G 350.329+0.100 2.5 –62 –64 G 350.331+0.099 3.9
G 350.686–0.491 G 350.686–0.491 0.4 G 350.686–0.491 1.3 –14 –14.5 –13.8
G 351.160+0.696 G 351.160+0.697 2.5 G 351.160+0.697 1.3 –3 –8.5 –5.2 G 351.161+0.696 3.0
G 351.243+0.671 G 351.243+0.671 3.4 –77 2.5
G 351.246+0.668 G 351.247+0.667 3.6
G 351.417+0.646 G 351.417+0.645 3.7 G 351.417+0.646 1.7 –10 –9.1 –11.2
G 351.417+0.645 3.1 –10.4
G 351.582–0.353 G 351.581–0.353 1.6 G 351.581–0.353n 2.1 –89 –97.6 –91.1
G 351.581–0.353 3.4 –94.4
G 351.775–0.536 G 351.775–0.536 1.8 G 351.775–0.536 1.9 –2 –2 1.3
G 352.111+0.176 G 352.111+0.176 2.8 –60 –54.8
G 352.133–0.944 G 352.133–0.944 2.8 –11 –16
G 352.162+0.199 G 352.161+0.200 1.0 –45 –42.2
G 352.517–0.155 G 352.517–0.155 0.2 G 352.517–0.155 0.3 –49 –50.6 –51.2
G 352.525–0.158 G 352.525–0.158 0.3 –51 –53
G 352.623–1.076 G 352.624–1.077 4.7 –6 5.8
G 352.630–1.067 G 352.630–1.067 0.5 G 352.630–1.067 0.4 0 0 –2.8
G 353.273+0.641 G 353.273+0.641 0.3 –49 –5.2
G 353.411–0.362 G 353.411–0.362 1.7
G 353.464+0.562 G 353.464+0.562 0.9 G 353.464+0.562 1.9 –60 –45 –50.7
G 354.615+0.472 G 354.615+0.472 1.9 G 354.615+0.472 1.8 –38 –15.4 –24.6
G 355.343+0.147 G 355.344+0.147 2.0 G 355.344+0.147 1.7 17 19 20
G 355.343+0.148 2.7 5.7
G 355.345+0.149 G 355.346+0.149 1.4 72 10
G 357.965–0.164 G 357.965–0.164 1.5 –19 –8.8
G 357.967–0.163 G 357.968–0.163 1.7 G 357.967–0.163 0.5 –65 –6.3 –3.2
G 358.371–0.468 G 358.371–0.468 1.0 1 1
G 358.386–0.483 G 358.387–0.482a 2.3 G 358.386–0.483 1.5 0 –6.3 –6.0 G 358.387–0.483 3.4
G 358.387–0.482b 3.3 –7.8
G 359.137+0.032 G 359.137+0.032 1.3 G 359.138+0.031 1.5 –1 –1 –3.9
G 359.436–0.102 G 359.436–0.102 0.4 –59 –53.6
G 359.436–0.104 G 359.436–0.103 1.9 G 359.436–0.104 0.7 –47 –52 –52
G 359.615–0.243 G 359.615–0.243 0.8 G 359.615–0.243 0.6 64 22.5 22.5
G 359.969–0.457 G 359.970–0.457 1.2 G 359.970–0.457 1.3 11 15.5 23.0
G 0.209–0.002 G 0.209–0.002 2.4
G 0.212–0.002 G 0.212–0.001 3.7 56 49.2
G 0.316–0.201 G 0.316–0.201 0.7 23 21
G 0.315–0.201 2.1 18
G 0.376+0.040 G 0.376+0.040 1.3 G 0.376+0.040 1.6 40 36 37.1
G 0.497+0.188 G 0.496+0.188 2.1 G 0.496+0.188 2.1 26 –5.5 0.8
G 0.547–0.851 G 0.546–0.852 2.7 G 0.546–0.852 3.2 20 13.5 13.8
G 0.657–0.042 G 0.658–0.042 0.4 G 0.657–0.041 4.8 62 52
G 0.668–0.035 G 0.666–0.035 4.0 59 61
G 2.143+0.009 G 2.143+0.009 0.8 G 2.143+0.009 0.1 37 59.8 62.7
G 2.536+0.198 G 2.536+0.198 2.5 25 3.2
G 5.886–0.392 G 5.885–0.392 6.3 G 5.885–0.392 5.5 11 13.9 6.7
G 5.901–0.430 G 5.900–0.430 1.7 14 10
G 6.049–1.447 G 6.048–1.447 2.0 20 11.2
G 6.611–0.082 G 6.610–0.082 2.1 6 0.7
G 6.796–0.257 G 6.795–0.257 2.1 G 6.795–0.257 2.4 1 16.1 26.6
G 8.139+0.226 G 8.139+0.226 1.2 16 20.0
Table 3: continued
Water OH Sep. Methanol Sep. Water OH Methanol Continuum Sep.
() () () Vpeak Vpeak Vpeak ()
(degrees) (degrees) (arcsec) (degrees) (arcsec) () () () (degrees) (arcsec)
G 8.670–0.356 G 8.669–0.356 2.9 G 8.669–0.356 2.7 36 39.2 39.3 G 8.670–0.356 1.1
G 9.620+0.194 G 9.620+0.194 1.6 6 22
G 9.622+0.195 G 9.621+0.196 2.9 G 9.621+0.196 3.3 22 1.4 1.3
G 9.986–0.028 G 9.986–0.028 1.3 49 47.1
G 10.288–0.125 G 10.287–0.125 1.9 9 5
G 10.323–0.160 G 10.323–0.160 1.5 –3 10
G 10.342–0.143 G 10.342–0.142 1.8 8 14.8
G 10.445–0.018 G 10.444–0.018 3.3 G 10.444–0.018 3.7 70 75.5 73.2
G 10.473+0.027 G 10.473+0.027 0.9 G 10.473+0.027 1.9 62 51.5 75 G 10.473+0.027 1.8
G 10.480+0.034 G 10.480+0.033 4.5 G 10.480+0.033 4.5 64 66 65
G 10.623–0.383 G 10.623–0.383 0.6 2 –2
G 10.959+0.022 G 10.958+0.022 1.4 25 24.4 G 10.959+0.022 0.7
G 11.034+0.062 G 11.034+0.062 1.6 G 11.034+0.062 1.5 18 21.7 20.6
G 11.498–1.486 G 11.497–1.485 2.9 17 6.7
G 11.903–0.142 G 11.904–0.141 3.5 G 11.904–0.141 4.4 36 40.5 42.8
G 12.203–0.107 G 12.203–0.107 0.2 35 20.5
G 12.209–0.102 G 12.209–0.102 1.0 22 19.8 G 12.209–0.102 3.0
G 12.216–0.119 G 12.216–0.119 1.5 26 27.9
G 12.681–0.183 G 12.680–0.183 1.0 G 12.681–0.182 1.1 61 64.5 57.6
G 12.889+0.489 G 12.889+0.489 3.0 G 12.889+0.489 2.7 30 33 39.3
G 12.908–0.260 G 12.908–0.260 1.2 G 12.909–0.260 1.8 37 38 39.9
G 17.637+0.156 G 17.638+0.157 2.1 G 17.638+0.157 2.2 27 20 20.7
Table 3: continued
Continuum RA(2000) Dec(2000) Ipeak Total Flux
() Density
(degrees) (h m s) ( ) (mJy/beam) (mJy)
G 291.611–0.529 11 15 02.62 –61 15 51.4 350 446
G 291.626–0.531 11 15 09.66 –61 16 15.7 137 357
G 299.012+0.128 12 17 24.12 –62 29 05.6 25 38
G 301.136–0.226 12 35 34.96 –63 02 31.6 1017 1116
G 311.643–0.380 14 06 38.73 –61 58 21.4 174 181
G 313.458+0.193 14 19 35.04 –60 51 52.1 205 272
G 316.412–0.308 14 43 23.25 –60 12 59.5 160 167
G 317.430–0.561 14 51 38.03 –60 00 19.5 32 35
G 319.399–0.012 15 03 17.60 –58 36 11.2 230 298
G 320.234–0.283 15 09 52.63 –58 25 32.4 282 293
G 327.402+0.445 15 49 19.35 –53 45 13.3 86 94
G 328.236–0.547 15 57 58.15 –53 59 23.4 26 36
G 328.307+0.431 15 54 06.24 –53 11 38.8 3361 3647
G 328.808+0.633 15 55 48.33 –52 43 07.0 1208 1357
G 330.879–0.367 16 10 19.95 –52 06 05.3 324 476
G 330.954–0.182 16 09 52.51 –51 54 54.1 2954 3151
G 331.443–0.187 16 12 12.83 –51 35 10.2 40 44
G 331.512–0.103 16 12 10.10 –51 28 37.2 109 113
G 332.826–0.549 16 20 11.12 –50 53 13.7 2510 2670
G 333.030–0.063 16 18 56.94 –50 23 53.5 27 25
G 333.466–0.163 16 21 19.71 –50 09 45.6 141 254
G 336.018–0.828 16 35 09.39 –48 46 47.6 85.1 80.8
G 336.360–0.137 16 33 29.64 –48 03 38.8 189 293
G 336.984–0.184 16 36 12.60 –47 37 57.8 51 56.8
G 336.990–0.025 16 35 32.48 –47 31 14.6 91 102
G 337.404–0.403 16 38 50.59 –47 28 02.8 117 121
G 337.706–0.054 16 38 29.83 –47 00 35.7 244 262
G 338.075+0.012 16 39 39.15 –46 41 26.2 818 1144
G 338.681–0.085 16 42 24.19 –46 18 00.4 74 74
G 344.582–0.024 17 02 58.03 –41 41 52.7 19 21
G 345.004–0.225 17 05 11.36 –41 29 06.5 353 355
G 345.010+1.792 16 56 47.85 –40 14 25.8 362 367
G 345.408–0.952 17 09 35.62 –41 35 54.6 493 608
G 347.632+0.210 17 11 36.22 –39 07 06.2 46 48
G 350.331+0.099 17 20 02.09 –36 59 12.8 55 65
G 351.161+0.696 17 19 57.65 –35 57 51.8 238 271
G 351.247+0.667 17 20 19.29 –35 54 39.4 1280 1567
G 353.411–0.362 17 30 26.66 –34 41 46.0 384 788
G 358.387–0.483 17 43 37.96 –30 33 49.2 109 113
G 0.209–0.002 17 46 07.57 –28 45 30.5 75 95
G 8.670–0.356 18 06 19.15 –21 37 32.1 677 689
G 10.473+0.027 18 08 38.41 –19 51 47.9 152 151
G 10.959+0.022 18 09 39.43 –19 26 27.0 150 153
G 12.209–0.102 18 12 39.85 –18 24 20.0 119 140
Table 4: 22-GHz continuum sources detected towards water maser sources (i.e. continuum sources within 4.5 arcsec of detected water masers). See Tables 1 and 3 for details of the water maser sources that these continuum sources are associated with. Columns one through to 5 show: the name of the continuum source in Galactic coordinates, the source right ascension, declination, peak flux density (mJy/beam) and integrated flux density (mJy). We present two additional continuum sources that fall just outside our association threshold and we distinguish these sources with a ’’ following the source name in column 1.

4 individual sources

Here we draw attention to information on the sources that can not be adequately conveyed in the tables and spectra. We discuss some entries in the Table 1 where close companions may be either discrete extra maser sites, or merely multiple features in an unusually extended site. Our interpretation of the likely systemic velocity, based on association with methanol or OH maser emission, is given in some cases where water shows high velocity features that dominate the spectrum. Extreme variability is sometimes evident from Table 1, and a few examples of this variability are demonstrated by spectra shown from both 2003 and 2004. The absence of an entry at one epoch is occasionally due to confusion from nearby features, as remarked in these notes. There are many instances where high velocity emission is present (as indicated in Table 1), but is rather weak and barely visible on the spectrum, so we draw attention to it here.

284.350–0.418. This water maser is coincident with main-line OH maser 284.351–0.418, with accompanying emission at 6035-MHz (Caswell, 1997), but clearly offset from nearby methanol maser 284.352–0.419 by 6 arcsec. Spectra from epoch 2003 as well as 2004 are shown as an example of the typical variability seen between our observing epochs.

285.260-0.067 and 285.263-0.059. The latter is a very strong water maser associated with an OH maser and having similar velocity of its strongest emission. In the case of OH masers this systemic velocity is a reliable indication of the systemic velocity. The first maser, offset by 1 arcmin, may be loosely associated, but it is difficult to recognise possible emission near the systemic velocity because of confusion with the stronger companion. Its spectrum varied markedly from 2003 to 2004, and highly blue-shifted emission dominates the 2004 spectrum.

290.374+1.661 and 290.384+1.663. The first of these sources is coincident with both OH and methanol maser emission. The positions measured in 2003 and 2004 are coincident, but detected features do not overlap in velocity ranges. There has been a substantial decrease in the peak flux density from 3.5 Jy to 0.26 Jy from the first to the second epoch.

The second source 290.384+1.663, is offset from the OH and methanol target and appears to be solitary, with no associated OH or methanol maser emission.

291.270–0.719, 291.274–0.709 and 291.284–0.716. The 2003 data for these sources are presented in Caswell (2004a), along with extensive discussion on associated sources. Note that the OH target 291.274–0.709 was a supplementary addition to the list of C98. The variability of the water masers between the two epochs is moderate, with minimal changes in the velocity ranges of the detected emission but many changes in the relative flux densities of individual features.

291.270–0.719 is associated with methanol maser emission and has weak emission near the systemic velocity but much stronger emission blue-shifted by almost 80 . 291.274–0.709, shows emission only near the systemic velocity and is coincident with both OH and methanol maser emission. The strongest source, 291.284–0.716, is associated with neither OH or methanol maser emission and shows no detectable water maser emission at the systemic velocity but has strong blue-shifted emission. Caswell & Phillips (2008) regard this source and 291.270-0.719 as members of a distinct class of water masers that are dominated by blue-shifted outflows.

291.578–0.434, 291.579–0.431 and 291.581–0.435. The main strong source 291.579–0.431 is a persistent maser detected in both 2003 and 2004, and also 1981 (Caswell et al., 1989), with intensity varying by a factor of 4. The other sources, detected at a single epoch, are even more variable. All are associated with NGC 3603 (Caswell, 2004a).

291.610–0.529, 291.627–0.529 and 291.629–0.541. The three water masers of this cluster were all detected both in 2003 and 2004 and are associated with NGC 3603 (Caswell, 2004a). Only G291.610–0.529 is coincident with an OH maser and none of the sources is associated with any methanol maser emission.

297.660-0.974. The strongest water maser peaks, at 29  in 2003 and 26  in 2004, agree well with the associated OH maser peak at 27.6 , the probable systemic velocity for the region. There is a weak high velocity water maser feature of 0.6 Jy at a velocity of –78 , slightly more than 100  from the systemic velocity.

299.012+0.125 and 299.013+0.128. 299.013+0.128, with strongest peak at +19  in both 2003 and 2004, was first detected by Caswell et al. (1989) and is in good agreement with the position and velocity of methanol and OH masers. In 2004 we detected an additional weak source, 299.012+0.125, offset by 9 arcsec. We regard the latter as most likely a distinct source, probably in the same cluster but lacking emission at its systemic velocity.

300.968+1.143 and 300.971+1.143. 300.968+1.143 was first observed by Caswell et al. (1989), with high velocity emission extending to –85 , remaining similar in our observations in both 2003 and 2004. This source is solitary, offset from the target OH maser by 18 arcsec. Observations in 2004 uncovered an additional source, 300.971+1.143, with a flux density of 3 Jy. As can be seen in Table LABEL:tab:masers, in 2003 we placed an upper limit on the flux density of this source of 3 Jy, quite crude because at this velocity there was confusion by strong emission from 300.968+1.143 at this epoch.

301.136–0.225, 301.136–0.226a, 301.136–0.226b and 301.137–0.225. Although we list four distinct water maser positions, they probably represent a single maser site, with the last three locations all within 3 arcsec of OH and methanol maser emission, Confusion between features in 2003 prevented separate position measurement of any but the strongest feature.

305.191–0.006 and 305.198+0.007. 305.198+0.007 is probably the same source as 305.20+0.01 in Caswell et al. (1989). Both of these water masers are offset from the target OH maser, 305.200+0.019 (with methanol maser, 305.199+0.005).

305.208+0.207 Two strong peaks have positions separated by about 1 arcsec, with the weaker peak slightly closer to the associated OH and methanol emission.

306.318–0.331. This is new solitary water maser source found offset from target OH and methanol maser positions by 15 arcsec.

308.754+0.549. The OH target is an addition to the C98 list. Details of methanol, OH and water are given by Caswell (2004a).

308.918+0.124. The position of this water maser falls within our 3 arcsec association threshold of OH maser G 308.918+0.123 but lies 3.6 arcsec from methanol maser G 308.918+0.123. The OH and methanol masers are almost certainly coincident, with a measured separation of 0.6 arcsec, and we treat all three species as coincident.

309.921+0.479. Caswell et al. (1989) reported the detection of a 4.5-Jy water maser at –70  towards this OH and methanol site. We detect no emission ( 0.3 Jy) in either 2003 or 2004.

310.144+0.760 and G 310.146+0.760. The first of this close pair of sources is located at the site of both OH and methanol maser emission and the second source is located at the site of an isolated 1720-MHz OH maser (Caswell, 2004c) and is strongly variable.

311.94–0.14. This is a methanol site from Caswell (2009) with position 14 07 49.72, -61 23 08.3 (uncertainty 0.4 arcsec) from which there was no water detection in 2003 (this position was not observed in 2004). However a water maser was reported by Caswell et al. (1989) with peak flux density 38 Jy from the position 14 07 49.9 -61 23 20, nominally offset from the methanol by 12 arcsec but with rms position uncertainty of about 10 arcsec and thus possibly coincident with the methanol. An OH maser is listed by C98 at 14 07 48.7 -61 23 22, nominally offset from the methanol by 16 arcsec, but again, possibly coincident (to within the OH position uncertainty of more than 15 arcsec). Like the water maser, the OH has varied, and later observations to attempt an improved position determination failed to detect it. We have omitted this source from the statistics since for our position coincidence threshold of 3 arcsec. it may be an OH site accompanied by water, by methanol, by both or by neither, depending on the precise positions yet to be determined.

312.106+0.278 and 312.109+0.262. The second source is located towards the targeted methanol maser and consists of a single feature, with velocity similar to the methanol. The first source is a slightly stronger single feature, offset from the second by nearly 1 arcmin, and clearly offset in velocity by 6 .

312.596+0.045 and 312.599+0.046. These sources are a close pair, separated by 10 arcsec. The second of these sources was also detected by Caswell et al. (1989) and is coincident with both OH and methanol masers. The first source, 312.596+0.045, is coincident with a methanol maser site.

313.457+0.193 and 313.470+0.191. These sources have an angular separation of 45 arcsec. 313.470+0.191 was also detected in Caswell et al. (1989) and is associated with both OH and methanol masers, with peak water maser velocity comparable to the systemic velocity of the region as traced by the coincident methanol maser with mid-range velocity of –8 . 313.457+0.193 has an emission peak near –1  at both epochs, suggesting its systemic velocity (and distance) is similar to that of its companion. We regard the slightly stronger emission at 45  seen only in 2004 as a strongly varying high velocity feature.

316.360–0.361 and 316.361–0.363. Near these water masers lie an isolated methanol site (316.381–0.379) and a ‘methanol with OH’ site (316.359–0.362). Water maser 316.360–0.361 is offset from the methanol in the latter pair by 3.2 arcsec, and slightly further from the OH. Thus the water maser is formally rejected as part of an intimate association, but this remains somewhat uncertain. The second water maser source is further offset from these sources than the first and is thus very clearly a distinct, isolated site.

318.044–1.404 The OH and methanol maser counterparts show that the systemic velocity is indeed near +45  and indicate a distant location outside the solar circle. The large latitude offset from the Galactic plane is consistent with the Galactic warp known to be present in this outer region of the Galaxy.

318.948–0.196a and 318.948–0.196b. This pair of sources is essentially one extended source. Using the 2004 data, we were able to distinguish two main sites (with an angular separation of just over 2 arcsec) which conveniently reveals the association with nearby OH and methanol masers that otherwise would have fallen outside our 3 arcsec coincidence threshold.

320.221–0.281, 320.232-0.284, 320.233-0.284, 320.255–0.305 and 320.285–0.308. We suggest that all 5 sites are at similar distance in a cluster with systemic velocity near –65 . 320.232-0.284 has associated methanol and OH maser emission and 320.233-0.284, offset by nearly 5 arcsec, seems to be a separate site. 320.255-0.305 shows strong emission only near –126 , highly blue-shifted from our suggested systemic velocity near –65 , and apparently in a small class of water masers where blue-shifted emission dominates (Caswell & Phillips 2008). Interestingly, like 291.284–0.716, 320.255–0.305 is not associated with either OH or methanol maser emission. Emission from this region was reported, with lower position precision, by Caswell et al. (1989).

321.028–0.484 and 321.033–0.483. Both water masers are offset from the target OH and methanol maser 321.030–0.485 by more than 7 arcsec; the second water maser is associated with methanol maser 321.033–0.483.

321.148–0.529 The spectrum of this maser is shown at both epochs as an example of extreme variability with no common features seen in spectra observed less than 1 year apart.

323.459-0.079. A water maser was discovered (but without a precise position) by Caswell et al. (1989) towards this OH and methanol site, but was below our detection threshold of 0.2 Jy in both 2003 and 2004.

324.716+0.342. This source was detected by Caswell et al. (1989) at a peak flux density of 138 Jy, coincident with both OH and methanol maser emission. The water maser shows marked variability with peaks of 10 and 26 Jy during 2003 and 2004 respectively.

326.662+0.521, 326.665+0.553 and 326.670+0.554. This group of three sources is spread over 2 arcmin. 326.670+0.554 coincides with an OH maser; the water maser peak flared in 2004 relative to 2003. This maser is probably the same as one reported, with peak of 780 Jy, but with poor position, by Batchelor et al. (1980). In 2004 no targeted observation was made of the first source and although recognised at the beam edge in another observation, it was confused by a strong flare from 326.670+0.554. Measurement for the second source (326.665+0.553) is reported only from the 2004 measurements since the 2003 observations were confused by 326.662+0.521, preventing a useful upper limit estimate.

326.780-0.241 This is a new water maser coincident with an OH maser listed by Caswell (1998) with approximate coordinates 326.77-0.26; subsequent (previously unpublished) ATCA measurements of the OH show it to be coincident with the water maser.

326.859-0.676. This weak new water maser coincides spatially with methanol maser 326.859–0.667 (offset by 3.4 arcsec), whose systemic velocity is –58.0 . It seems likely to be an association in which only a heavily blue-shifted water maser feature, at –103 , is seen.

327.291-0.578. This strong water maser with peak of several hundred Janskys is associated with OH and methanol masers. Spectra are shown for 2003 and 2004 revealing great variability of the water maser, and can be compared with a spectrum shown by Batchelor et al. (1980) when its peak was over 1000Jy.

327.402+0.445. In contrast to the previous source, this water maser has greatly increased intensity compared to measurements by Batchelor et al. (1980). The water maser is associated with a strong methanol maser. An OH maser is close to the methanol. We therefore treat the OH as an association also, although its separation from the water is just outside our formal association criterion.

328.306+0.432. This water maser is associated with 22-GHz radio continuum but appears to be truly offset from the target OH maser 328.307+0.430 (which has no accompanying methanol) by more than 5 arcsec.

328.808+0.633. Detected towards OH maser site 328.809+0.633. Also associated are many transitions of methanol and OH, including; 6.6-, 12.2-, 19.9-, 85.5- and 107-GHz methanol masers (Caswell 2009; Caswell et al. 1995; Ellingsen et al. 2004; Ellingsen et al. 2003; Val’tts et al. 1999) as well as 1720-, 4765-, 6030-, 6035-MHz and 13.4-GHz transitions of OH (Dodson & Ellingsen 2002; Caswell 2003, 2004b, 2004c). This source is also associated with strong 22-GHz radio continuum.

329.021–0.186, 329.029–0.199, 329.030-0.205 and 329.031–0.198. This cluster of four sources is spread over about 1 arcmin. The first source is solitary (no OH or methanol), the second (which varied below the detection limit in 2004) has OH, and the third and fourth are associated with both OH and methanol. Ellingsen (2006) showed that these OH, methanol and previously known water masers are associated with a filamentary infrared dark cloud as well as Class I methanol masers.

329.342+0.130. This water maser is clearly offset by almost 1 arcmin from the target OH maser 329.339+0.148 and no other water emission was detectable in the field. The water maser velocity is similar to that of its OH neighbour and they presumably reside in the same star formation cluster, discussed in detail by Caswell (2001, 2004). Note that the OH target is an addition to the C98 list.

329.404–0.459, 329.405–0.459 and 329.407–0.459. The second source is at an OH and methanol maser site, and its velocity is similar, presumably representative of the systemic velocity. The first source is offset only 3 arcsec from the second site, whereas its velocity is close to that of the previously discussed, more distant, cluster around 329.339+0.148. None the less, we suggest it most likely represents high velocity emission related to 329.405–0.459. Water maser 329.407–0.459, associated with a methanol maser, has shown extreme variability with peak flux density of 80 Jy in 2003 but not detected above our detection limit of 0.2 Jy in 2004.

329.421–0.167, 329.424–0.164 and 329.426–0.161. The only other maser species nearby, both spatially and in velocity, is a 1720-MHz maser 329.426–0.158 (Caswell, 2004c). We conclude that all four masers lie in the same star forming cluster but are not closely associated.

330.879–0.367 The water maser has been known for many years (Batchelor et al. 1980) and our precise position confirms that it coincides with one of the strongest known OH masers, accompanied by very weak methanol emission (Caswell 2009).

330.954–0.182. The water maser has remained very strong for many years (see Batchelor et al. (1980)) and has prominent high velocity emission (a feature at -191  has a peak flux density of 0.3 Jy but is too weak to be seen on the spectra displayed here). OH and methanol emission are present nearby but spread over several arcsec, and the most detailed maps (Caswell et al. 2010) show the water to be associated with OH emission only, with the methanol emission clearly offset to another site offset to the south-west by more than 3 arcsec. We measure the flux density at 22-GHz of an associated strong UCHii region as 3.2 Jy.

331.418+0.252. This 0.6-Jy water maser was detected almost 50 arcsec from the targeted methanol maser 331.425+0.264. The water maser emission is observed towards an UCHii region that we detect at 22-GHz.

331.512–0.103. Batchelor et al. (1980) observed this source with a peak flux density of 4300 Jy. Observations of this source in 2003 and 2004 showed a decrease in the flux density to 700 Jy and 534 Jy in 2003 and 2004 respectively. The water maser is coincident with an OH maser (but no methanol) and an UCHii region that we detect. The strongest water emission is near the systemic velocity, and almost symmetric about this there are multiple high velocity features extending for 70 .

332.826–0.549. This is a strong new water maser coinciding with methanol and a 6035-MHz OH maser but offset 7 arcsec from a 1665-MHz OH maser.

333.219–0.062 and G 333.234–0.060. 333.234–0.060 was detected in both 2003 and 2004 and has been previously observed by Batchelor et al. (1980). At all epochs the peak has been more than 100 Jy at a velocity near -88 , which is the mid-range velocity of an associated OH maser, and the likely systemic velocity. In our 2004 water observations, an extreme high velocity feature was observed with a peak flux density of 0.3 Jy at +81 , more than 160  from the systemic velocity. 333.219–0.062 is offset from 333.234–0.060 by almost an arcmin and is solitary. This source was observed with a peak flux density of 0.5 Jy in 2004 and was not detected in 2003 above 0.3 Jy. In the absence of an association with OH or methanol, its systemic velocity is unknown.

333.387+0.032. This weak water maser is located at the site of both OH and methanol maser emission. It was detected with a peak flux density of 0.4 Jy in 2003 and had decreased to 0.14 Jy in 2004. Spectra from both epochs are presented in Fig. 1.

333.608–0.215. This was one of the earliest observed water masers, discovered by Johnston et al. (1972) and was later observed by Batchelor et al. (1980) in 1976 with a peak flux density of 100 Jy. Breen et al. (2007) carried out interferometric observations of this source in 2006, deriving a precise position for the source that is within 0.4 arcsec of the independent position quoted in Table LABEL:tab:masers. Both the Breen spectrum of 2006 and that found in the present observations of 2003 differ markedly from the 2004 spectrum shown here, revealing strong variability of high velocity emission. This source is associated with an OH maser and is offset by 15 arcsec from a bright UCHii region which was erroneously reported by Breen et al. (2007) as having an integrated flux density of 631 mJy at 22 GHz. The present observations find that the UCHii region has an integrated flux density of more than 16 Jy at 22-GHz.

333.930–0.134. This very weak water maser was observed at the 2004 epoch only. While the peak of the detected emission is a mere 0.18 Jy, the source position is in remarkably good correspondence with the targeted methanol maser, the separation being less than 1.5 arcsec.

335.059–0.428, 335.060–0.427 and 335.070–0.423. The first two of these sources are separated by 3.3 arcsec and therefore may be essentially a single source spread over a few arcsec. The second source, 335.060–0.427, with measurements in both 2003 and 2004, shows best positional agreement with an associated OH and methanol maser site. 335.059–0.428 was not recognisable as a distinct source in the 2003 data owing to confusion from the stronger companion 335.060–0.427.

335.070–0.423 is offset from the previous two sources by 43 arcsec and is solitary.

335.585–0.285, 335.586–0.290 and 335.588–0.264. These three sources are spread over almost 80 arcsec. The first two sources were detected at both epochs and are both coincident with both methanol and OH masers. The third source, 335.588–0.264, was detected with a peak flux density of 16 Jy in 2003 but not detectable above 0.2 Jy in 2004. It is isolated from other maser species and is devoid of detectable 22-GHz radio continuum emission.

335.787+0.177, 335.789+0.174 and 335.789+0.183. 335.789+0.174 was detected by Batchelor et al. (1980) as a 25 Jy source towards an OH maser with the same Galactic coordinates. Our observations detect a water maser of 3 Jy in 2003 and detect no emission above 0.2 Jy in 2004. 335.787+0.177, detected in both 2003 and 2004, is a solitary maser and has no detectable radio continuum at 22-GHz. The third source, 335.789+0.183, is also isolated from other maser species as well as 22-GHz radio continuum emission. It was detected with a peak flux density of 4.2 Jy at a velocity of –91  in 2003 and was not detectable above 0.2 Jy in 2004. If this velocity represents the systemic velocity, then its distance is likely to differ greatly from its apparent companions. Alternatively, it may be a companion at similar distance but showing no significant emission near the systemic velocity, and only blue-shifted emission. Such high velocity features are notoriously variable.

336.864+0.005, 336.864–0.002 and 336.870–0.003. These three sources are located within 40 arcsec of each other and were all detected in both the 2003 and 2004 observations. The first source is associated with both OH and methanol maser emission and the other two sources are solitary.

336.983–0.183. Figure 1 shows both the 2003 and 2004 spectrum for this weak source. The only significant feature in 2003 is a peak at –76 . In 2004, emission near this velocity is weaker, and a high velocity feature near +45  is marginally stronger. The source is associated with a methanol maser as well as an UCHii region that we list in Table 7. The methanol maser is strong, with a well-measured position and velocity near –81 . Nearby is a weak OH maser just outside our criterion for an association with the water position, but slightly closer to the methanol. Furthermore, the position of 6035-MHz OH emission (Caswell 2001) is acceptably within our coincidence criterion, so we add this as an OH maser association with both methanol and water.

336.991–0.024, 336.994–0.027 and 336.995–0.024. These three sources appear clustered within 15 arcsec. 336.994–0.027 is the strongest of the three (160 Jy), detected in 2003, 2004 and by Batchelor et al. (1980), and is associated with both OH and methanol maser emission, with systemic velocity near -120 . The 2 weaker water sites have quite different radial velocities, near -50 , and might be at a distance quite different from the strongest one. 336.991–0.024 was detected in both 2003 and 2004, with a peak flux density of 4 and 1 Jy at the respective epochs, and is associated with an UCHii region that we detect. 336.995–0.024 was detected only in 2004 and had a peak flux density of 1.1 Jy.

337.994+0.133 and 337.998+0.137. Batchelor et al. (1980) detected 337.998+0.137 with a peak flux density of 200 Jy and we detected a decreased flux density of 30 and 27 Jy in 2003 and 2004 respectively. This source is coincident with both OH and methanol maser emission. 337.994+0.133 is a solitary maser, offset from the previous source by 19 arcsec.

338.069+0.011, 338.075+0.012, 338.075+0.010 and 338.077+0.019 Water maser emission from 338.069+0.011 is the strongest in this cluster at both epochs and has no other maser counterpart. 338.075+0.012 detected only in 2003, and the weakest of the group, coincides with OH and methanol maser emission. 338.075+0.010 is associated with a methanol maser with systemic velocity near -38 ; the water maser emission in 2003 was strongest at a highly blue-shifted velocity, but by 2004 this had faded below detectability, leaving only features closely straddling the systemic velocity. 338.077+0.019 was detected in both 2003 and 2004, the spectrum remaining unchanged; it has no apparent association with other masers.

338.920+0.550 and 338.925+0.556 The stronger site, 338.925+0.556 coincides with OH and methanol masers. The weaker site, 338.920+0.550, is associated with a methanol maser with systemic velocity near -60 , similar to the other site, and the water spectrum in 2003 was dominated by highly blue-shifted emission.

343.126–0.065 and 343.127–0.063. These two sources are separated by 9.3 arcsec. The second source is strong and associated with an OH maser, but not methanol. The first source is much weaker but clearly distinct and is solitary.

345.004-0.224 In 2003 the only water emission was near the systemic velocity, as defined by the associated methanol and OH masers. In 2004, high velocity features dominated. Spectra from both epochs are shown to demonstrate this interesting variability.

345.010+1.793, 345.010+1.802 and 345.012+1.797 In this small cluster, the first water maser coincides with an OH and methanol site, the second has no other maser counterpart, and the third, the strongest, has a methanol counterpart.

345.397-0.950, 345.402-0.948, 345.405-0.947, 345.406-0.942, 345.408-0.953, 345.412-0.955 and 345,425-0.951 One of these sites, 345.425-0.951, is coincident with a methanol maser site. We also accept a coincidence between 345.408-0.953 and an OH and methanol maser site, despite an offset of 4.6 arcsec, formally just outside our our criterion for a single epoch water measurement; there is evidence (from comparison of features common to 2003 and 2004, and a feature common to 2004 and FC89) that the 2004 observation of this field yields positions slightly too far south and at too large an RA, a correction that would improve the coincidence. The systemic velocity of the two associated, methanol sites is near -15 . In view of the large offset of the cluster from the Galactic plane in Galactic latitude, all water sites are likely to be clustered at a similar distance, irrespective of the water maser velocity. Their separation from each other is sufficiently large to suggest that each site has its own exciting star, and thus it seems likely to be a remarkable physical cluster of massive stars. Radhakrishnan et al. (1972) suggest that the distance to the complex is half the distance to the Galactic Centre.

345.487+0.314. As seen in the notes tabulating associations, there is a coincident methanol maser and no nearby ground-state OH maser. There is, however, a 6035-MHz excited state OH maser offset just over 3 arcsec to the north (Caswell 2001).

345.493+1.469, 345.494+1.470 and 345.495+1.473 The first site coincides with an OH maser that has no accompanying methanol maser. Another nearby OH maser site shows no methanol or water emission. All four sites are likely to lie in a nearby cluster, as evident from the large Galactic latitude, and the systemic velocity probably lies between -15 and 0 , based on the OH velocities.

347.623+0.148 and 347.628+0.149 The first water maser, detected in both 2003 and 2004, has no coincident maser of OH or methanol. The second water maser, at similar velocity, was detected only in 2003 and coincides with OH and methanol, with systemic velocity near -95 .

348.533–0.974, 348.534–0.983 and 348.551–0.979 The third water site is close to the original OH target but is more precisely coincident with the methanol site 348.550-0.979n (Caswell 2009). The original ‘OH with methanol’ target, 348.550-0.979, is regarded by Caswell (2009) as a nearby but distinct site and, on this interpretation, it is a site without detected water maser emission. The water masers 348.533–0.974 and 348.534–0.983 are new, chance, detections in the vicinity.

348.726–1.038 This water maser is offset from the target OH (with methanol) by more than 4 arcsec and is not formally an association. However, the large spread over several arcsec in the positions of individual water maser spots reveals a larger than usual maser site and the possibility of an association will require further investigation.

350.105+0.084 350.112+0.089 and 350.113+0.095 The first of these is associated with a methanol site, and the second with an OH site. In a cluster of 6 water maser sites showing peak emission at velocities between -72 and -44 , they are the only 2 accompanied by maser emission of another species. Spatially in this same cluster, the water maser 350.112+0.089 displays a quite different velocity range, from -175 to -106  suggesting that it might be at a quite different location, perhaps in the near side of the 3-kpc arm, whose characteristic velocity at this longitude extends to approximately -110  (Green et al. 2009); see also the note for 351.582–0.353.

350.299+0.122. This is the weakest single epoch water maser that we list, with a peak flux density of 0.17 Jy. The position of the water maser is only 0.7 arcsec from the targeted methanol maser and its emission peak velocity of –68  is within 6  of the associated methanol maser peak emission. Furthermore, there are no nearby water maser sources that could confuse the region and be detected as a sidelobe here; there is therefore little doubt that this is a genuine weak water maser.

351.240+0.668, 351.243+0.671 and 351.246+0.668 The first 2 sites were listed by Caswell & Phillips (2008), with special discussion of a blue-shifted outflow that dominates the emission from 351.243+0.671, and remarks that the water maser spots in the outflow are distributed over several arcsec. All three sites appear to be distinct, with large separations of more than 15 arcsec, yet close enough to suggest that they all lie in the same star-forming cluster, with systemic velocity +2.5 as defined by the methanol maser counterpart to 351.243+0.671 (Caswell & Phillips 2008), and all lying in the large NGC 6334 complex, at a commonly accepted distance of 1.7 kpc

351.417+0.645 This maser coincides with an HII region NGC 6334F, a very strong methanol maser, and an OH maser (Caswell 1997) and its water maser emission was mapped by Forster & Caswell (1999), showing a scatter of spot positions over several arcsec, including an apparent jet-like feature.

351.582–0.353 This strong water maser is coincident with an OH and methanol maser site which is located in the near side of the expanding 3-kpc arm (Green et al. 2009; Caswell et al. 2010).

352.623-1.076 and 352.630-1.067 The second water maser coincides with an OH and methanol site. It flared from a peak of 35 Jy in 2003 to 700 Jy in 2004. It appears to be the same maser that was first reported by Sakellis et al. (1984) with peak flux density 346 Jy. The first source is solitary with no other maser counterpart and offset by more than 40 arcsec.

353.273+0.641 This site is the prime example of a class of water maser dominated by a blue-shifted outflow (Caswell & Phillips 2008); its systemic velocity is estimated from a coincident methanol maser.

353.408–0.350 to 353.414–0.363 inclusive This is a cluster of 6 solitary water maser sites. The target OH and methanol maser site 353.410–0.360 (Caswell 1997) lies in this cluster but none of the water maser sites coincide with it.

354,703+0.297, 354.712+0.293 and 354,722+0.302 The velocity of all three solitary water sites is near +100 , similar to that of the nearby OH with methanol site 354.724+0.300. The velocity of the latter has been interpreted as evidence of a location in the the Galactic bar (Caswell 1997), which we suggest is an appropriate interpretation for all 4 sites.

357.965–0164 and 357.967–0.163 The two water sites are separated by 9 arcsec. The first site has a weak methanol counterpart but no OH; the second has stronger methanol and also OH. The methanol and OH emission is confined to a small range between –9 and +3 , and thus the systemic velocity for both sites probably lies in this range. Water emission at the first site was strong in 2003 but weak in 2004, and confined to within about 15  of the systemic velocity. Water emission at the second site is seen not only near the systemic velocity but also at many blue-shifted and red-shifted high velocities; in 2004 the high velocity features were stronger than emission near the systemic velocity.

359.436–0.102 to 359.443–0.104 inclusive The six water maser sites in this cluster all have similar velocities. Confusion prevented a useful upper limit estimate for emission from 2 of them not detected in 2003. One site has an OH with methanol counterpart and another, a methanol counterpart. The methanol sites appear to be located in the near side of the 3 kpc arm (Green et al 2009) and this interpretation can be applied to all six water sites in the cluster.

0.655–0.045 to 0.677–0.028 These five sites lie within the Sgr B2 complex and are clearly distinguishable with our spatial resolution. Two of them have associated OH maser emission but none have associated methanol masers.

5.886–0.392 This site has OH and water masers spread over more than 5 arcsec, associated with a compact HII region that is likely to be approaching the end of its masing phase (Caswell 2001) and with various distance estimates, of which 2 kpc is currently favoured (Stark et al. 2007). It was observed by Forster & Caswell (1989; 1999) and our 2003 water maser observations were made to assess the changes over a decade. We cite the position of the strongest feature during our observations and note that there are many components at offset positions. Our water reference position and the OH reference position from Caswell (1998) are 6 arcsec apart but we list it as an association with OH on the basis of the intermingled features mapped by Forster & Caswell (1999).

9.620+0.194 and 9.622+0.196 These coincide respectively with an OH maser site with no reported methanol, and the strongest known methanol site which also has a coincident OH maser. A third methanol maser site in this cluster, 9.619+0.193, shows no detectable water maser emission.

10.473+0.027 and 10.480+0.034 The first source was detected in both 2003 and 2004, and the spectrum shown is from 2004 when a strong flare occurred. The spectrum shown for 10.480+0.034 is from 2003 when 10.473+0.027 was not flaring, and confusion from 10.473+0.027 was much less.

10.623–0.383. Note a small correction to the C98 OH position, for which the RA should be 181028.67 (not 28.61). Our water measurement in 2003 is in good agreement with the revised OH position and the measurement of FC89.

11.903-0.141. We detect a weak water maser at this site which is probably the same source that was first reported by Caswell et al. (1983) with peak flux density 7.9 Jy (but with position uncertainty exceeding 10 arcsec). Note a small transcription error in the target OH position from FC89, FC99 and C98, for which the RA should be 181211.46 (not 11.56). Our water maser position is in satisfactory agreement with the corrected OH position. The corrected OH position also agrees better with the 6035-MHz maser position (C97), and with its associated UCHii region (C97) for which improved measurements by Forster & Caswell (2000) at 8.7 GHz give a flux density of 33.9 mJy.

15.016–0.679 to 15.034-0.667 inclusive These all reside in the well-known nearby star-forming complex M17. All seven masers were recognisable and spatially distinct in the 2004 observations but only 3 were distinct in the 2003 observations, partly due to the stronger confusing emission from 15.028–0.673 at the earlier epoch. Spectra for the two strongest sources from the 2003 epoch are shown in Fig. 1 and are in addition to the 2004 spectra.

5 Discussion

5.1 Water maser variability

Water masers have been noted on many occasions for their often extreme variability over relatively short timescales, and some studies have extended over several decades (e.g. Felli et al., 2007). As our data are confined to only two epochs, and limited to coarse spectral resolution, we do not attempt a detailed study of the variability of our sources. However, we are able to highlight some interesting examples of variability, and the large size of our sample allows us to derive several interesting statistics.

For the 207 sources observed and detected at both epochs, we see variability ranging from sources showing no measurable variability to occasional extreme levels, and many intensities varying by factors of more than two. High velocity features can be particularly variable, with many spectral features of sources not being common to both epochs.

As noted in Section 3, Fig. 1 includes the spectra of eight sources from both epochs (284.350–0.418, 321.148–0.529, 327.291–0.578, 333.387+0.032, 336.983–0.183, 345.004–0.224, 15.026–0.654 and 15.028–0.673). They illustrate changes seen over the 10-month time scale and highlight the fact that, for four of the examples, the feature with the strongest peak at the two epochs is at a different velocity.

A qualitative impression from the full set of spectra at both epochs (including our unpublished material for the 2003 epoch) is that the spectra of many sources show little resemblance at the two epochs. Quantitatively, we use the data of Table 1 to derive the plot of Fig.  2 which compares the velocity of the water maser peak emission in 2003 and 2004. An interesting statistic for the sources measured at two epochs shows that the strongest peak is at a significantly different velocity (offset more than 2 ) for 38 per cent (78 of 207) of the sites. However, from Fig. 2 we see that a much smaller fraction of velocity differences exceed 10 . These large velocity differences generally represent the truly high velocity features which, in a few sources, can dominate the spectrum at some epochs since they have highly variable intensities. For example, the source 357.967-0.163 has the 2003 peak intensity at 0 (near systemic) but the 2004 peak at -65 (a high velocity feature); and the source 336.983-0.183 has the 2003 peak intensity at -76 (near systemic) but the 2004 peak at +45 (a high velocity feature).

Figure 2: 2004 peak water maser velocity versus 2003 peak water maser velocity. Overlaid is a solid line with a slope of 1 and two dashed lines showing a deviation of 10  either side of the solid line.

We have observations available in both 2003 and 2004 for 253 water masers; 46 of them (17 per cent) were detected at only one epoch. Only 16 (one-third) of these sources that varied below our detection limit at one of the epochs were stronger than 2 Jy when detectable, with the strongest source being 80 Jy. Half of the sources detected only at one epoch show a single feature and the majority of the others exhibited 3 or fewer features. In comparison, the vast majority of water maser sources that are associated with OH or methanol masers exhibit five or more spectral features. We have investigated the associations with other maser species for these 46 sources to search for other possible properties in common. Of the 46 sources, 12 are associated with both OH and methanol masers, 2 are associated with OH masers only, 3 are associated with methanol masers only and 28 are solitary (no association with another maser species). A chi-squared test was carried out on the percentage of sources in each of these groups compared to what would be expected if these sources were distributed in the same way as our entire sample. We find that a statistically significant higher percentage of the sources detected at only one epoch are solitary (p-value 0.02), compared to the distribution of associations in our full sample. The numbers of sources that varied below the detection limit at one epoch and are associated with combinations of OH and/or methanol masers are as expected from the distribution of the entire sample.

Claussen et al. (1996) suggested that water masers associated with low mass stars were in general both weaker and more variable than those associated with high mass stars. As we find that the sources only detectable at one epoch are biased towards solitary sources and are in general relatively weak, it is possible that a number of these water masers are in fact associated with lower mass stars perhaps residing in the same stellar clusters as the high mass star formation regions towards which the observations were targeted (see also end of Section 5.6 and Section 5.7).

The potential of water masers for mapping the distribution of massive SFRs throughout the Galaxy has been demonstrated for a few sources by astrometry sufficiently precise to achieve parallax measurements and precise distances (e.g. Sato et al. 2008). Water masers appear to provide the largest population to make these investigations, but with several caveats. Firstly, a site must have individual maser spots persisting for more than a year. Despite the extreme variability shown by all spots at some sites, and some spots at most sites, our data reassuringly demonstrate that there still remain an enormous number of suitable sites. A second reservation concerns the ability to associate a systemic velocity with the precise distance, enabling mapping of the Galactic velocity field. As we shall see in Sections 5.3 and 5.4, the estimate of the systemic velocity for an isolated water maser is uncertain, but an excellent estimate can be obtained from the OH or methanol masers accompanying many water masers. Note that the spatial correspondence between maser species is usually sufficient to yield very high confidence associations, whereas associations with more diffusely distributed thermal emission in molecular clouds are less reliable. So, associated OH or methanol masers are the key to establishing the systemic velocity of a water maser. We note that for sites with OH but no methanol, parallax determinations are beyond present capabilities except through the use of associated water masers. And even for some methanol sites, it may turn out that an associated water maser provides the best parallax measurement. Thus the important role of water masers in these Galactic studies is assured.

5.2 Spatial distributions of maser spots

The VLA study of water masers by FC89 and FC99 examined the distributions of maser spots, both in velocity and spatially, for the masers that were quite strong and/or displayed many spectral features. It was shown that, where many maser spots were present, they lay either within a diameter rarely exceeding 30 mpc, or in a few clusters of this size separated by distances at least several times larger. The quite large beamsize used in the present observations precludes detailed study of the spot distributions, but allows recognition of clusters with several distinct members, of which there are many. We do however, find a substantial number of water maser sources that show distinguishable angular separations between clusters of maser spots emitting near the systemic velocity, and those emitting at high velocities. The separations are generally of the order of 2 or 3 arcsec, and are plausibly attributed to associated outflowing material. Occasionally, separations between systemic and high velocity components exceed 4 arcsec, and even in these cases it seems credible that these are associated outflows.

5.3 Detection statistics and relationship to ground-state OH and methanol masers

The position measurements and new detections of water masers reported in Table LABEL:tab:masers mostly arose from a search at all the positions of southern SFR maser sites with ground-state OH main-line (1665 and 1667-MHz) masers that had not previously been searched. The target list corresponded to table 1 of C98, plus a few modifications which we briefly summarise here. Small position corrections were needed for 10.623-0.383 and 11.904-0.141; and an improved (previously unpublished) position has been determined for 326.780-0.241, listed by C98 at the approximate position 326.77-0.26. The list was augmented by 291.274–0.709, 308.754+0.549 and 329.339+0.148 (see notes for these sources in Section 4 and Caswell (2001)). The OH source 311.94+0.14 still has no precise position measurement and, although searched for water, has been omitted from the statistics, as discussed under the note on 311.947+0.142.

Because the observations were targeted toward OH masers detected in a blind search, the detection statistics can be meaningfully computed. The new search has established sensitive upper limits for water masers toward 42 main-line OH maser sources, and a net detection rate for water masers towards OH masers of 79 per cent. Additional observations were made towards a selection of 104 methanol masers with no reported OH counterpart (chiefly from Caswell, 2009).

As noted in Section 3, of the 379 detected water maser sources, 128 are associated with both OH and methanol masers, 33 are associated with OH masers only, 70 are associated with methanol masers only and 148 are solitary (i.e. not associated with either OH or methanol maser emission). The water maser detection rate towards sources exhibiting both OH and methanol maser emission is 77 per cent (128 of 166). In contrast, the water maser detection rate towards OH maser sites (with no methanol) is 89 per cent (33 of 37). In order to determine if water masers were preferentially detected towards OH masers without associated methanol masers we carried out a chi-squared test. The resultant p-value of 0.6 means that the higher detection rate of water masers towards OH maser sources without associated methanol is not statistically significant.

Because the sample of methanol masers targeted in 2004 was not homogeneous, it is difficult to draw strong conclusions concerning methanol/water associations from the detection statistics. However, the fact that we find 70 associations of water towards methanol masers without OH (from a total sample of 104), and 33 associations of water towards OH masers with no methanol (from a total sample of 37), along with a detection rate of 77 per cent towards sources exhibiting both OH and methanol masers, indicates that the overlap between the lifetimes of water, OH and methanol masers is large. A possible interpretation is that during the evolution of the star the methanol masers are not only the first maser species to appear but also the first species to turn off whereas the OH and water both persist for longer.

Water Average flux Median flux
classification density (Jy) density (Jy)
all sources 57.1 5
with OH 96.1 15
with methanol 68.3 9
with continuum 74.9 18
only OH 138.2 25
only methanol 26.1 3.5
solitary 18.9 2.8
Table 5: The average and median water maser flux densities for all the sources we detect.

Table LABEL:tab:fluxcomp presents both the average and median flux densities of the water masers that we detect, broken up into categories according to their association with OH and methanol masers as well as 22-GHz radio continuum. Where a source was detected in both 2003 and 2004 we have used the two recorded values of flux density as separate entries. In column 1 the types of association are listed. Here ‘all sources’ incorporates all water maser peak flux densities detected at either epoch; ‘with’ OH, methanol or continuum refers to water masers that are associated with the afore-mentioned source but not limited to associations with only these sources; ‘only’ OH or methanol incorporates only those water maser sources exclusively associated with either OH or methanol masers, but places no restrictions on their association with 22-GHz radio continuum; and ‘solitary’ refers to water sources that are not associated with either OH or methanol masers. We find that there is trend of increasing water maser flux density from solitary sources to sources associated with methanol masers to sources associated with OH masers and 22-GHz radio continuum. This may indicate that the water masers increase in flux density as the sources evolve, similarly to that found by Breen et al. (2010) for 6.6-GHz methanol masers. We note, however, that the average and median flux density of the solitary water masers is likely to be at least partly due to some of these sources being associated with low-mass stars.

The recent completion of the Southern Hemisphere component of the Methanol Multibeam (MMB) survey (Green et al. 2009; Caswell et al. 2010) for 6.6-GHz methanol masers will soon provide an even more extensive catalogue of SFRs than the OH catalogue of Caswell (1998) to search for associated water maser emission. The MMB survey is the most sensitive survey yet undertaken for young high-mass stars in the Galaxy and is complete within 2 degrees of the Galactic plane. Water maser observations towards this unbiased catalogue of methanol masers will enable meaningful detection statistics for methanol and water maser associations to be derived and allow comparison with our statistics derived from the comparison of OH and water maser associations. Due to this, coupled with the fact that our methanol targeted sample is not homogeneous, we do not attempt to draw further conclusions from this methanol sample. We anticipate that comparisons between the sources detected in the MMB survey and infrared data, in conjunction with follow-up observations for 22-GHz water masers, 12.2-GHz methanol masers and other non-masing molecular species will uncover unique insights into the differing physical conditions responsible for the presence/absence of the different methanol maser transitions.

Beuther et al. (2002) conducted a high resolution study of the water and methanol masers in 29 massive star formation regions and found that 10 methanol masers coincide spatially with water masers to within their uncertainty of about 1.5 arcsec. They remarked that no spatial correlations exists between the two maser species, which is clearly not an inference from their results and refers presumably to the common expectation that detailed correlations of maser spots is unlikely.

Our finding is that occurrence of a water maser at nearly 80 per cent of the OH maser targets is comparable to the occurrence of methanol at OH targets. This might seem surprising in view of the difference in favoured pumping schemes, where both OH and methanol depend on far IR radiation, whereas the favoured pumping scheme for water masers is collisional (Elitzur, Hollenbach & McKee 1989). However, it is consistent with the expectation that in most locations where methanol and OH masers occur there are coincident, or nearby, shocked regions with high densities suitable for the excitation of water masers. Pursuing this further, the apparently larger number of water masers than other maser species is consistent with the extremely common occurrence of such shocked regions, not only in the envelope of a high-mass star, but also in outflows and in lower mass stars with less IR flux.

Interestingly, pumping of the formaldehyde masers (which are uncommon, but also trace SFRs) is unclear, since the Boland & de Jong (1981) radiative pump seems deficient and may need shocks and collisions, according to Hoffman et al. (2003).

5.4 Velocity distributions of maser features

Figure 3: OH maser peak velocity versus methanol maser peak velocity. Overlaid is a solid line with a slope of 1 and two dashed lines showing a deviation of 10  either side of the solid line.

The velocity distributions for the water masers have intrinsic interest but are most fruitfully studied in comparison with OH and methanol counterparts where available. The velocity range of water maser emission at many sites is larger than for OH or methanol, with the velocity range of water masers measured in 2003 having an average of 27  and a median of 15  and those measured in 2004 showing an average velocity range of 30  and a median of 15 . In contrast, methanol masers rarely show emission that exceeds a velocity range of 16  (Caswell, 2009), and C98 found the median velocity range of 100 OH masers with flux densities greater than 2.7 Jy to be 9 .

Sometimes the water emission is remarkably symmetric about the systemic velocity but, more often, is asymmetric. The strongest water maser emission is generally confined to the velocity ranges of the associated OH and methanol masers. The velocity of methanol maser emission is regarded as a reliable indication of the systemic velocity for the regions that these masers are tracing (e.g. Caswell, 2009; Pandian, Menten & Goldsmith, 2009), allowing kinematic distances for the sources to be computed. OH masers are slightly less reliable tracers of systemic velocities because small changes to the apparent radial velocity are caused by the Zeeman effect. Water masers however, are generally regarded as unreliable tracers of systemic velocities, as they commonly trace high velocity outflows and have large velocity ranges.

We first compare the peak velocities of methanol and OH masers in Fig. 3, (using the population of 165 sources studied in this paper, including sources both with and without associated water maser emission). This clearly demonstrates the close similarity in the velocity of their peaks. The average difference between the peak velocities of the OH and methanol masers is 3.4 , with a median difference of 2.2 .

We now compare the velocity of the peak emission of our large sample of water masers with the peak of associated OH and methanol masers (Figs 4 and  5, respectively). The 2004 peak velocities were used where possible and 2003 peak velocities were used otherwise. In the case of 160 OH-water maser associations, we find that the average difference in the peak velocities is 7.8  and the median difference is 4 . In the case of 197 methanol-water maser associations we find that the average difference in the peak velocities is 8.8  and the median difference is 4.2 . Thus for the majority of sources there is quite good correspondence between the velocity of the peaks of water masers and those of the associated OH or methanol maser peak emission, but there are some striking outliers.

Comparison of Fig. 3 with Figs 4 and 5 highlights the closer correspondence between the peak velocities of the OH and methanol masers than either of these species compared to the associated water maser peak velocity. 93 percent of the OH and methanol maser peak velocities are in agreement to within 10 , whereas for the water-methanol and water-OH peak velocities this number falls to 78 and 79 per cent.

We now look in more detail at the outlying sources in Figs 4 and 5. The isolated source at the lower right of the plots is 336.983–0.183 and, as remarked in the note of Section 4, the high-velocity water feature is accompanied by emission at the systemic velocity (methanol and OH peak velocity) which is of comparable intensity (or stronger at the 2003 epoch). Disregarding this source, Fig. 4 shows only a small number of dominant high-velocity features (offset more that 30 ) with no preference for red or blue shifts. In Fig. 5, we distinguish the sources with only methanol from those with OH as well as methanol. We note that there is a striking group of six highly blue-shifted features of which five have no OH emission. These are some of the distinct population of dominant blue-shifted outflows discussed by Caswell & Phillips (2008).

5.5 Clustering of maser sites and association with other masers of OH

In addition to the water maser sources that we find to be intimately associated with the OH and methanol masers that were targeted, we frequently detect water masers separated from the target OH and methanol masers by 10 arcsec or more. Furthermore, we find the occurrence of multiple water maser sites within the HPBW of the ATCA primary beam to be common, with the number of sources often exceeding two and reaching as high as seven. Fig. 6 shows a histogram of the number of water masers in the targeted ATCA fields that are solitary (i.e. in addition to the water masers detected at the targets of OH and methanol). There are 90 cases where there is one or more solitary maser within the HPBW of a target OH or methanol maser. This means that observations targeted towards OH and methanol masers have a 29 per cent chance of detecting at least one unrelated water maser within 2 arcmin of the target source.

Clusters comprising combinations of water, OH and methanol masers spread over 20 arsec are common. Comparative studies of sites within these clusters, where we can infer that near-contemporaneous formation of several massive stars has occurred, hold promise for unravelling the preferred environments and stellar evolutionary stages for different maser species; future studies of water masers and associated IR sources will play a major role in this investigation.

Six sites of 1720-MHz maser emission, believed to be of the SFR variety but with no other maser species, were listed by Caswell (2004c), and these have also been searched for water masers. A new water maser was detected towards one of them, 310.146+0.760, as well as towards its cluster companion the OH 1665-MHz and methanol maser 310.144+0.760, offset nearly 10 arcsec. The 1720-MHz maser 329.426-0.158 was previously the only maser detected in a putative SFR (with an HII region nearby both spatially and in velocity). Although no water was found at the 1720-MHz site, two new water maser sites were discovered, with offsets of only 20 arcsec, and therefore credibly within this SFR and therefore now increasing its known maser population to a cluster of three masers.

Two sites that currently are known as masers only at the 6035-MHz excited-state of OH were also searched for water. No water detection was made towards either 311.596-0.398 or 345.487+0.314.

Figure 4: Water maser peak velocity versus OH maser peak velocity. Overlaid is a solid line with a slope of 1 and two dashed lines showing a deviation of 10  either side of the solid line. An additional pair of lines (dotted) shows a deviation of 30 .
Figure 5: Water maser peak velocity versus methanol maser peak velocity. Overlaid is a solid line with a slope of 1 and two dashed lines showing a deviation of 10  either side of the solid line. An additional pair of lines (dotted) shows a deviation of 30 . We distinguish sources with only methanol (cross) from those with OH as well as methanol (dot).
Figure 6: Histogram of the number of solitary water masers detected in single ATCA fields.

5.6 Association with continuum UCHii regions

The present observations, although focused on spectral line emission, also allowed a search at each maser site for an associated UCHii region, to a limit of  30 mJy if the region is not too confused. Although this is two orders of magnitude less sensitive than can be achieved with a targeted wide bandwidth survey (Forster & Caswell 2000), it is at higher frequency, and provides in many cases a useful first estimate.

The sensitivity to radio continuum is not uniform for all sources, and is especially poor for observations with maser emission over an extensive velocity range, leaving little of the bandpass free from line emission. Due to this, and our short integration times we are sensitive only to relatively strong UCHii regions.

We have not used the continuum data collected at the 2003 epoch since the uv-coverage (with an EW array) was significantly poorer than achieved with the H168 array in 2004. The 29 water maser sources observed only during the 2003 observations have therefore been removed from the subsequent statistics. Table LABEL:tab:contcomp presents the number of water maser sources observed in 2004, broken up into the categories of solitary, associated with an OH maser, associated with both OH and methanol masers, and associated with a methanol maser (numbers shown in column 2). Column 3 shows the number of water maser sources in each category that are also associated with 22-GHz radio continuum from UCHii regions that we detect, while column 4 shows the percentage of sources with detectable 22-GHz radio continuum in each category. We find associations with UCHii regions, indicative of an embedded massive early type star, for 42 of the water maser sources that we detect.

Due to the targeted nature of this search, with the OH sample being complete but the methanol sample incomplete, percentages are presented in Table 5 to reveal more clearly the correlations. The percentages of water maser sources with associated UCHii region in Table LABEL:tab:contcomp show that UCHii regions are preferentially detected toward water maser sources with associated OH masers.

Water # of sources # of sources % with
association total (2004) with cont cont
OH & methanol 112 24 21.4
OH 28 6 21.4
methanol 67 5 7.5
solitary 143 7 4.8
Table 6: Comparison between water maser associations and the presence of associated 22-GHz radio continuum. Column 1 describes the water maser associations, column 2 shows the number of water maser sources observed in 2004 that fall under the given association. Column 3 gives the number of sources within each category that are associated with 22-GHz radio continuum and column 4 shows this number as a percentage of the water maser sources in each category.

We find that our overall detection rate for UCHii regions towards water maser sources with associated OH masers (with or without associated methanol) is 21.4 per cent while our detection rate towards water maser sources without associated OH masers (solitary or with methanol) is 5.0 per cent. Forster & Caswell (2000) conducted a sensitive search at 8.7-GHz for UCHii regions towards OH and water masers which showed that 52 per cent of the OH masers they targeted had an associated UCHii region. While our observations are almost two orders of magnitude less sensitive than was achieved by Forster & Caswell (2000), they are at a higher frequency allowing us to potentially detect emission from hyper-compact (HC) H ii regions which are typically optically thick at centimetre wavelengths. Comparison with the detection rate of Forster & Caswell (2000) suggests that a more sensitive search at 8.7-GHz for UCHii regions towards our OH maser associated water maser sources would more than double our detections from 30 sources to 71.

Our results support arguments (Caswell (2001); Beuther et al. (2002); Breen et al. (2010)) that methanol maser emission is often seen prior to any OH maser emission, but is sensitive to the onset of emission from UCHii regions, and less able to survive the later stages of the evolution of the UCHii region. Carrying on these arguments to include water masers we find that the water masers are also present at the early stages of formation, like the methanol masers, prior to the onset of OH maser emission. These statistics for solitary water sites naively suggest that these water masers precede the onset of strong UCHii regions. However, as mentioned in Section 5.1, it is possible that a significant population of the solitary water masers are associated with low mass stars and this provides an alternative explanation.

5.7 Comparison with GLIMPSE objects

Association with GLIMPSE point sources

We have compared the positions of the 379 water maser sources with the positions of sources in the GLIMPSE point source catalogue. We find that 343 of our water maser sources are within the Galactic longitude and latitude ranges observed by GLIMPSE and that 165 of these are within 3 arcsec of a GLIMPSE point source (48 per cent). This number increases to 211 if sources from the GLIMPSE archive are included (62 per cent). The fraction of the water maser sources associated with point sources contained in either the GLIMPSE point source catalogue or the supplementary archive catalogue, is similar to that found by Ellingsen (2006) when comparing the positions of 56 methanol masers with GLIMPSE sources (68 percent).

We have further investigated the associations between water maser and GLIMPSE sources by comparing the GLIMPSE source association rates of water masers in their association categories (i.e. associated with both OH and methanol masers, associated with OH masers, associated with methanol masers etc.). Association rates are as follows:

  • 76 of the 165 GLIMPSE detections have both OH and methanol (i.e. 46% of the GLIMPSE sources are associated with OH, methanol and water and 60% of the OH methanol and water sources have an associated GLIMPSE source).

  • 91 of 165 GLIMPSE detections have OH detections (i.e. 55% of the GLIMPSE sources have an associated OH maser and 57% of OH maser sources have an associated GLIMPSE source).

  • 109 of 165 GLIMPSE detections have methanol detections (i.e. 66% of the GLIMPSE sources have an associated methanol maser and 56% of methanol maser sources have an associated GLIMPSE source).

  • 18 of 165 GLIMPSE detections have associated radio continuum (i.e. 11% of the GLIMPSE sources have an associated HII region and 43% of HII regions have an associated GLIMPSE source).

  • 41 of 165 GLIMPSE detections only have an associated water maser (i.e. 25% of the GLIMPSE sources are only associated with a water maser and 29% of the water only sources have an associated GLIMPSE source).

The GLIMPSE point source association rates are similar in all categories except for solitary water masers and water masers associated with radio continuum where the association rates are significantly lower. In the case of the radio continuum, it is likely that a large number of sources exhibiting strong radio continuum would no longer be point sources at mid-infrared frequencies (because sources exhibiting strong radio continuum are likely to be more evolved) and this would therefore account for the lower association rate. The lower association rate between GLIMPSE point sources and solitary water masers could be explained by a tendency for these water sources to be associated with more extended objects, or, alternatively, that the solitary water masers are commonly associated with lower luminosity sources.

Figure 7 shows a plot of the [3.6]–[4.5] m versus [5.8]–[8.0] m colours of the GLIMPSE point sources associated with the water masers. Flux density measurements for all four of the IRAC bands had to be available for the inclusion in this plot thus limiting the plotted sample to 14 solitary water masers (i.e. with no methanol or OH maser counterpart) and 58 water masers with either a methanol or an OH counterpart. We find, similarly to previous comparisons (e.g. Ellingsen, 2006; Breen et al., 2010), that the GLIMPSE sources associated with the masers are located above the majority of the comparison sources in the colour-colour plot. This figure also reveals an apparent difference in the ranges of the [3.6]–[4.5] m colours for solitary water masers compared with water masers that are associated with methanol, OH or continuum (or a combination of these).

We have carried out a t-test (testing the hypothesis that there is no difference between the means) on both the [3.6]–[4.5] and [5.8]–[8.0] m colours of those GLIMPSE sources associated with solitary water masers compared to those associated with water masers as well as OH, methanol or radio continuum. In the case of the [5.8]–[8.0] m colours we find that there is no statistically significant difference between the values associated with the two groups of water maser sources. For the [3.6]–[4.5] m colours we find that there is a statistically significant difference (p-value 0.007) between the GLIMPSE sources associated with solitary water masers and those water masers with associated methanol, OH or radio continuum sources.

As can be seen in Fig. 7, the [3.6]–[4.5] m colour tends towards smaller values in the case of the solitary water masers. Since there is no difference in the [5.8]–[8.0] m colours between the two groups of sources this means the solitary water maser associated GLIMPSE sources have a much less steep spectrum at wavelengths m than at wavelengths greater than this. This indicates that these sources may be colder in general. Another explanation may be that the GLIMPSE sources associated with the solitary water masers have a relative excess of 4.5 m flux density, similar to extended green objects (EGOs) (Cyganowski et al., 2008).

In Section 5.1 we suggested that some fraction of the solitary water masers are likely to be associated with low-mass stars rather than the high-mass star formation regions where these observations were targeted. According to Cyganowski et al. (2008), GLIMPSE is too shallow to detect emission from outflows associated with low-mass stars (except perhaps for the closest low-mass star formation regions). Furthermore, if GLIMPSE detected infrared emission associated with low-mass stars it certainly would not detect it as a point source because the space density would be much too high. We therefore conclude that none of the sources included in Fig. 7 are associated with low-mass stars and therefore can not be responsible for the difference. However, it is possible that the lower association rate for solitary water maser sources with GLIMPSE point sources is partially because some fraction of the solitary water maser sources are associated with low-mass stars.

Figure 7: Colour-colour plot of GLIMPSE point source data. Water maser sources with associated OH and/or methanol maser emission are represented by red circles and solitary water maser sources are represented by the blue squares. The black dots represent all of the GLIMPSE point sources within 30 arcmin of l = 3265, b = 00.

Association with extended green objects (EGOs)

We have compared the locations of the EGOs presented in Cyganowski et al. (2008) with our 379 water masers. In order to avoid large numbers of chance associations between EGOs and water masers, we consider an EGO to be associated with a nearby water maser when the angular separation is less than 10 arcsec. Cyganowski et al. (2008) compared the locations of 6.6-GHz methanol masers with the images of their EGOs and show that this separation captures most of the associations while minimizing the chance coincidences that would result from a larger threshold. We find that 63 of the water masers are coincident with an EGO identified by Cyganowski et al. (2008).

Water % of full % of sources
association sample with EGOs
OH & methanol 33.8 55.6
OH 8.7 7.9
methanol 18.5 20.6
solitary 39.0 15.9
Total 100 100
Table 7: Comparison between water maser associations in our full sample with water maser associations for sources associated with EGOs. Column 1 describes the water maser associations, column 2 shows the percentage of water maser sources in each category (from the full sample) and column 3 gives the percentage of sources in each category that are also associated with an EGO (Cyganowski et al., 2008).

Table LABEL:tab:egos shows in the second column the percentage of the full sample of 379 water masers that fall within the four categories: associated with both OH and methanol masers, associated with only OH masers, associated with only methanol masers, and solitary; and in the third column, the number of water sources in each category that are also associated with EGOs as a percentage of the total number EGO-associated sources. This table shows that those water maser sources coincident with EGOs and associated with only methanol or OH masers are distributed in similar fashion to our complete sample of water masers, with little difference between the percentage of water sources presented in columns two and three. However, in the case of the solitary water sources, the association rate with EGOs is much lower than would be expected (similar to solitary water masers associated with GLIMPSE point sources). The absence of EGO associations with a large number of the water maser only sources may suggest that solitary water masers are associated with lower luminosity sources. Alternatively, considering that the water maser only sources tend to be associated with GLIMPSE point sources with dominant 4.5 m emission, a characteristic shared by EGOs, the water maser only sources may represent a class of younger sources, the majority of which have not yet produced an extended outflow. Perhaps this indicates that these solitary water masers are associated with outflow related sources: compact green objects, pre-cursors to EGOs.

We find that there is a higher association rate with EGOs for those water maser sources accompanied by both methanol and OH masers. This indicates that EGOs persist into the stage of star formation that is evolved enough to have produced an OH maser but not so evolved that the production of an associated strong UCHii region has caused the methanol maser emission to cease. Eighty-nine of the water maser sources we detect that are associated with both OH and methanol masers are within the regions covered by GLIMPSE and have been inspected for the presence of EGOs (Cyganowski et al., 2008). We find that 35 of these 89 sources are associated with an EGO, a rate of 39 per cent. This lends further credence to the idea the EGOs are not exclusively tracing the earliest stages of massive star formation but persist well into the stage where OH masers are present. Furthermore, as there is a large number of these objects, they must have a significant lifetime.

6 Conclusions

From a large sample of water masers measured with precise positions at two epochs, we conclude that spectra are highly variable but positions are generally persistent.

The occurrence of a water maser at nearly 80 per cent of the OH maser targets is comparable to that of methanol at OH sites. This is despite the difference in favoured pumping schemes, where both OH and methanol depend on far IR radiation, whereas the favoured pumping scheme for water masers is collisional.

Our study of water masers at methanol maser sites is preliminary, but the common presence of water at methanol sites is confirmed. We argue that there is indeed an important role for water masers in mapping the Galaxy and its velocity field. The present contribution of a large number of water masers with accurate positions in the southern Galaxy has been an important step in advancing such a project, and reveals the value of conducting even larger future surveys with complete Galactic plane coverage.

Acknowledgments

The Australia Telescope Compact Array is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. This research has made use of: NASA’s Astrophysics Data System Abstract Service; the NASA/ IPAC Infrared Science Archive (which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration); and data products from the GLIMPSE survey, which is a legacy science program of the Spitzer Space Telescope, funded by the National Aeronautics and Space Administration.

Footnotes

  1. pagerange: LABEL:firstpageLABEL:lastpage
  2. pubyear: 2010

References

  1. Batchelor R. A., Caswell J. L., Haynes R. F., Wellington K. J., Goss W. M., Knowles S. H., 1980, Aust. J. Phys., 33, 139
  2. Beuther H., Walsh A., Schilke P., Sridharan T. K., Menten K. M., Wyrowski F., 2002, A&A, 390, 289
  3. Boland W., de Jong T., 1981, A&A, 98, 149
  4. Braz M. A., Epchtein E., 1983, A&AS, 54, 167
  5. Braz M. A., Scalise E., 1982, A&A, 107, 272
  6. Breen S. L., Ellingsen S. P., Johnston-Hollitt M., Wotherspoon S., Bains I., Burton M. G., Cunningham M., Lo N., Senkbeil C. E., Wong T., 2007, MNRAS, 337, 491
  7. Breen S. L., Ellingsen S. P., Caswell J. L., Lewis B. E, 2010, MNRAS, 401, 221
  8. Caswell J. L., 1997, MNRAS, 289, 79 (C97)
  9. Caswell J. L., 1998, MNRAS, 297, 215 (C98)
  10. Caswell J. L., 1999, MNRAS, 308, 683
  11. Caswell J. L., 2001, MNRAS, 326, 805
  12. Caswell J. L., 2004a, MNRAS, 351, 279
  13. Caswell J. L., 2004b, MNRAS, 352, 101
  14. Caswell J. L., 2004c, MNRAS, 349, 99
  15. Caswell J. L., 2009, PASA, 26, 454
  16. Caswell J. L., Batchelor R. A., Haynes R. F., Huchtmeier W. K., 1974, Aust. J. Phys., 27, 417
  17. Caswell J.L., Phillips C.J., 2008, MNRAS, 386, 1521
  18. Caswell J.L., Vaile R.A., Forster J.R., 1995, MNRAS, 277, 210 (CVF95)
  19. Caswell J.L., Batchelor R.A., Forster J.R., Wellington K.J., 1983, Aust.J.Phys., 36, 443
  20. Caswell J.L., Batchelor R.A., Forster J.R., Wellington K.J., 1989, Aust.J.Phys., 42, 331
  21. Caswell J.L., Vaile R.A., Ellingsen S.P., Norris R.P., 1995, MNRAS, 274, 1126
  22. Caswell J. L. et al., 2010, MNRAS (in press)
  23. Claussen M. J., Wilking B. A., Benson P. J., Wootten A., Myers, P. C., Terebey, S., 1996, ApJS, 106, 111
  24. Cyganowski C. J. et al., 2008, AJ, 136, 2391
  25. Dodson R. G., Ellingsen S. P., 2002, MNRAS, 333,307
  26. Ellingsen S. P., Voronkov M. A., Cragg D. M., Sobolev A. M., Breen S. L., Godfrey P. D., 2007, IAU Symposium, 242, 213
  27. Ellingsen S. P., 2006, ApJ, 638, 241
  28. Ellingsen S. P., Cragg D. M., Lovell J. E. J., Sobolev A. M., Ramsdale P. D., Godfrey P. D., 2004, MNRAS, 354, 401
  29. Ellingsen S. P., Cragg D. M., Minier V., Muller E., Godfrey P. D., 2003, MNRAS, 344, 73
  30. Elitzur, M, Hollenbach, D.J., McKee, C,F., 1989, ApJ, 346, 983
  31. Felli, M., et al. 2007, AAP, 476, 373
  32. Forster J.R., Caswell J.L., 1989, A&A, 213, 339 (FC89)
  33. Forster J.R., Caswell J.L., 1999, A&ASuppl., 137, 43 (FC99)
  34. Forster J.R., Caswell J.L., 2000, ApJ, 530, 371
  35. Genzel R., Downes D., 1977, A&AS, 30, 145
  36. Green J. A. et al., 2009, MNRAS, 392, 783
  37. Hoffman I.M., Goss W. M., Palmer P., Richards A.M.S., 2003, ApJ, 598, 1061
  38. Hofner P., Churchwell E., 1996, A&AS, 120, 283
  39. Kaufmann P. et al., 1976, Nature, 260, 360
  40. Johnston K. L., Robinson B. J., Caswell, J. L., Batchelor R. A., 1972, ApL, 10, 93
  41. Pandian J. D., Menten K. M., Goldsmith P. F., ApJ, 2009, 706, 1609
  42. Radhakrishnan V., et al. 1972, ApJS, 24, 49
  43. Reid M. J., Schneps M. H. Moran J. M. Gwinn C. R. Genzel R., Downes D., Roennaeng B., 1988, ApJ, 330, 809
  44. Sato M., et al. 1994, PASJ, 60, 975
  45. Sault R. J., Teuben P. J., Wright M. H., 1995, ASP Conf. Ser. 77, Ed. Shaw R. A., Payne H. E., Hayes J. J. E., 433
  46. Val’tts I. E., Ellingsen S. P., Slysh V. I., Kalenskii S. V., Otrupcek R., Voronkov M. A., 1999, MNRAS, 310, 1077
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