Extreme submillimetre starburst galaxies

Extreme submillimetre starburst galaxies

Michael Rowan-Robinson , Lingyu Wang, Duncan Farrah, Dimitra Rigopoulou, Carlotta Gruppioni, Mattia Vaccari, Lucia Marchetti, David L. Clements
Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
SRON, Groningen 9747 AD, Netherlands
Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
Department of Astrophysics, University of Oxford, Keble Rd, Oxford OX1 3RH
INAF, - Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy
Astrophysics Group, University of the Western Cape, Private Bag X17, 7535, Bellville, Cape Town, South Africa
Department of Physical Science, The Open University, Milton Keynes MK7 6AA, UK
E-mail: mrr@imperial.ac.uk
Abstract

We use two catalogues, a Herschel catalogue selected at 500 m (HerMES) and an IRAS catalogue selected at 60 m (RIFSCz), to contrast the sky at these two wavelengths.

Both surveys demonstrate the existence of extreme starbursts, with star-formation rates (SFRs) . There appears to be a maximum (un-lensed) star-formation rate of 30,000 . IRAS sources with estimates higher than this are either lensed systems, blazars, or erroneous photometric redshifts.

At redshifts 3 to 5, the time-scale for the Herschel galaxies to make their current mass of stars at their present rate of formation , so these galaxies are making a significant fraction of their stars in the current star-formation episode. Using dust mass as a proxy for gas mass, the Herschel galaxies at redshift 3 to 5 have gas masses comparable to their mass in stars.

We have plotted here the individual spectral energy distributions (SEDs) for the 58 extreme starbursts in our Herschel survey, for which we have more complete SED information. Over 50 are QSOs or have an AGN dust torus, i.e. are Type 2 AGN, but in all cases the infrared luminosity is dominated by a starburst component. We derive a mean covering factor for AGN dust as a function of redshift and derive black hole masses and black hole accretion rates. There is a universal ratio of black-hole mass to stellar mass, , driven by the strong period of star-formation and black-hole growth at z = 1-5.

keywords:
infrared: galaxies - galaxies: evolution - stars:formation - galaxies: starburst - quasars: supermassive black holes - cosmology: observations

1 Introduction

A key discovery of IRAS was the prevalence of very luminous starburst galaxies. Galaxies with infrared luminosities were defined to be ultraluminous (Soifer et al 1984, Houck et al 1985), and those with luminosities were defined to be hyperluminous (Rowan-Robinson et al 2000, Rowan-Robinson and Wang 2010). Submillimetre selected samples from Herschel show the existence of even more extreme objects (Rowan-Robinson et al 2016). Here we use infrared template modelling to select sources on the basis of their star-formation rate rather than their infrared luminosity. Extreme starburst pose a problem for semi-analytic models of galaxy formation because the observed number-density of galaxies with star-formation rates substantially exceed the model predictions (Dowell et al 2014, Gruppioni et al 2015, Henriques et al 2015, Asboth et al 2016, Lacey et al 2016).

Two very different infrared surveys have highlighted the existence of extreme starbursts, with star-formation rates extending up to 30,000 . The Revised IRAS Faint Source Survey Redshift (RIFSCz) Catalogue (Wang et al 2014a) is a 60 m survey for galaxies over the whole sky at , which incorporates data from SDSS, 2MASS, WISE, and Planck all-sky surveys to give wavelength coverage from 0.36-1380 m. Since publication of Wang et al (2014a) Akari fluxes have been added to the catalogue, using a search radius of 1 arc min. An aperture correction needs to be applied to Akari 65 and 90 m fluxes to give consistency with IRAS photometry (Rowan-Robinson and Wang 2015). The optical and near-infrared photometry of 1271 catalogued nearby galaxies has been improved, following a systematic trawl through the NASAIPAC Extragalactic Database. Wang et al (2014) found that 93 of RIFSCz sources had optical or near infrared counterparts with spectroscopic or photometric redshifts. Table 1 summarises the number of RIFSCz galaxies by waveband.

(m) survey no. of sources
3.4 WISE 48603
4.6 WISE 48603
12 WISE 48591
12 IRAS 4476
22 WISE 48588
25 IRAS 9608
60 IRAS 60303
65 AKARI 857
90 AKARI 18153
100 IRAS 30942
140 AKARI 3601
160 AKARI 739
350 PLANCK 2275
550 PLANCK 1152
850 PLANCK 616
1380 PLANCK 150
Table 1: RIFSCz catalogue by band

The HerMES survey (Oliver et al 2012) allows us to construct a 500 m sample of galaxies in areas in which we have optical and infrared data from the Spitzer-SWIRE survey (Rowan-Robinson et al 2014, 2016). Selection at 500 m, rather than say 250 m, gives us greater visibility of the high redshift universe and has the benefit of ensuring detection also at 350, and in most cases 250, m, to give valuable SED information. The complete HerMES-SWIRE (Lockman+XMM+ES1+EN1+CDFS) 500 m catalogue consists of 2181 galaxies, of which 275 are lensing candidates. In the Lockman+XMM+ES1 areas there are a further 833 good quality 500+350 m sources which are not associated with Spitzer-SWIRE galaxies, for which Rowan-Robinson et al (2016) have estimated redshifts from their submillimetre colours. Table 2 contrasts the extragalactic sky as seen at 60 and 500 m.

The COSMOS survey (Scoville et al 2007) area was also part of the HerMES SPIRE survey and the full COSMOS photometric survey has been published by Laigle et al (2016). Photometric redshifts have been discussed by Ilbert et al (2013) and Laigle et al (2016). Scoville et al (2016) have used these data to analyse gas masses and star formation rates from z = 1-6. The approach, based on monochromatic luminosities at 850 m and CO (1-0) luminosities, glosses over the subtleties of variations of optical depth between sources which we try to capture through radiative transfer modelling of multi-wavelength SEDs (see also the discussion by Berta et al 2016). Pearson et al (2017) have used COSMOS data to discuss deblending and cross-identification issues for Herschel SPIRE data and, like Rowan-Robinson et al (2014, 2016), use the optical to mid-infrared SED data to inform the association process. There are 181 500 m sources with flux greater than 25 mJy, the flux limit we used in Rowan-Robinson et al (2016), and which also have 350 m detections, in the 2.0 sq deg of the COSMOS survey. All have 24 m associations. This yields a 500 m source-density of 90 per sq deg, similar to that found in the 26.3 sq deg of our sample.

Schulz et al (2017) have published a new IPAC SPIRE catalogue (HPSC) which analyses data taken in all Herschel SPIRE programmes in a homogeneous way. This would appear to offer the opportunity of a much larger sample of SPIRE galaxies. We used the HPSC catalogue to create a 250-350-500 m list as in Rowan-Robinson et al (2014). When we associated this list with the SWIRE photometric redshift catalogue (Rowan-Robinson et al 2013), we found only about half of the 2181 sources. This is an issue acknowledged in the HPSC explanatory supplement, which they attribute to blending of SPIRE sources in their detection procedure.

We also associated this HPSC 500 m catalogue with RIFSCz, finding 1640 associations. Many of these were also detected by Planck and so we can make a direct comparison of 350 and 500 m fluxes in the two surveys. We find that we need an aperture correction of k*delmag, where delmag = is the J-band aperture correction and k=0.15 at 350, and 0.10 at 500 m, to get agreement of SPIRE and Planck fluxes. Previously Wang et al (2014) reported the need for aperture corrections to be applied to WISE fluxes at 12 and 22 m. The latest version of RIFSCz (http:astro.ic.ac.uk:publicmrrfssreadme) thus provides a comprehensive collection of fluxes, with aperture corrections where necessary, from optical (SDSS), near infrared (2MASS), mid and far infrared (WISE, IRAS, Akari), through to submillimetre and millimetre (Herschel and Planck).

Section 2 of this paper discusses lensed galaxy diagnostics, section 3 discusses stellar mass, dust (and gas) masses and star formation rates, section 4 discusses extreme starbursts and section 5 discusses the role of AGN.

A cosmological model with =0.7, =0.72 has been used throughout. If we were to use (Planck 2015) luminosities and star-formation rates would be increased by 15.5.

Figure 1: S24/S500 versus S3.6/S500 for Hermes-SWIRE galaxies (Lock+XMM+ES1+CDFS+EN1) with 0.150.95. Red filled circles: lensing candidates,large black filled circles: galaxies with standard cirrus components, blue filled circles: galaxies with cool cirrus components, magenta filled circles: galaxies in Lockman (Rowan-Robinson et al 2014) with cold cirrus components, small black dots: non-cirrus galaxies.

2 Lensed galaxy diagnostics

Table 2 shows a comparison of the sky seen at 60 and at 500 m. The most striking aspects of 500m selection are (i) a much higher fraction of high redshift galaxies (Franceschini et al 1991), (ii) a much higher fraction of lensed objects (Blain et al 2002), (iii) a much higher fraction of galaxies with cool or cold dust (RR et al 2010, 2016, Rowan-Robinson and Clements 2015).

IRAS-FSS HerMES-SWIRE
60 m 500 m
no. of sources 60303 2181
area (sq deg) 27143 26.3
Lensing surface-density 0.001 per sq deg 10 per sq deg
Ultraluminous 8 70
Hyperluminous 0.7 25
Cirrus galaxies 42 34
of which, cooler dust 6 85
z 3 4 88
Table 2: Contrast between 60 and 500 m

Figure 1 illustrates the 3.6-24-500 m diagnostic ratios used by Rowan-Robinson et al (2014) to select lensed objects. It is a plot of S500S24 versus S3.6S500, with candidate lensed objects shown in red, normal cirrus galaxies shown in black, galaxies with cool dust shown in blue and galaxies with cold dust shown in magenta. The colour selection shown, with others, is remarkably effective at identifying lensing candidates. Details of the table of the 275 HerMES-SWIRE (Lock+XMM+ES1+CDFS+EN1) lens candidates are given at http:http:astro.ic.ac.ukpublicmrrspiresfr readmespirerev

For IRAS FSS (RIFSCz) sources we can not use this colour-colour diagnostic. Instead the infrared luminosity, or inferred star-formation rate, is a good indicator of lensing. There do not seem to be any cases where the true, unlensed star-formation rate is (see section 3 and Fig 2R below). Table 3 lists 22 RIFSCz objects with the star-formation rate, calculated by the automated template-fitting code, . 4 are known lenses. One (F14218+3845) has been imaged with HST and shows no evidence of lensing (Farrah et al 2002): Rowan-Robinson and Wang (2010) point out that there is a discrepancy between the ISO 90 m flux and the IRAS 60 and 100 m fluxes and if the former is adopted a much lower SFR (4,400 ) is obtained. 3 are blazars, for which the submillimetre emission is non-thermal, one object is more probably associated with a z=0.032 Zwicky galaxy, and three have photometric redshifts 4 which their SEDs show are implausible: these 7 have been removed from Fig 2R). We are left with 10 new candidate lenses, of which 5 have spectroscopic redshifts.

name RA dec z nirtem SFR note
F02416-2833 40.953415 -28.343891 1.514000 2 4.54
F03445-1359 56.718334 -13.844521 (1.14) 3 4.54
F08105+2554 123.380363 25.750853 1.512380 3 5.08 L
F08177+4429 125.316353 44.333546 (2.65) 5 5.78
F08279+5255 127.923744 52.754921 3.912200 3 6.89 L
F10018+3736 151.207672 37.362133 1.684160 3 5.30
F10026+4949 151.469330 49.579998 1.120000 3 4.54
F10119+1429 153.657822 14.251303 1.550000 3 5.01
F10214+4724 156.144012 47.152695 2.285600 2 5.05 L
F10534+3355 164.055649 33.661686 (1.17) 3 4.50
F13445+4128 206.656906 41.225357 (1.33) 3 4.75
F13510+3712 208.286133 36.964321 1.311000 3 4.70
F14132+1144 213.942673 11.495399 2.550000 3 5.80 L
F14218+3845 215.981201 38.530708 1.209510 3 4.98 U
F23265+2802 352.262146 28.312298 (1.90) 3 5.50
F02263-0351 37.221718 -3.626988 2.055000 3 5.51 blazar
F00392+0853 10.453402 9.173513 (4.62?) 3 7.19? alias at z=1.4
F06389+8355 102.896248 83.865295 (4.50?) 3 6.83? alias at z=1.2
F13080+3237 197.619431 32.345490 0.998010 3 4.52 blazar
F15419+2751 236.008347 27.697693 (2.02) 3 5.55 Zwicky gal z=0.032
F16360+2647 249.522308 26.694941 (4.55?) 3 7.23? z=0.066 2MASS gal at 0.27’
F22231-0512 336.446899 -4.950383 1.404000 3 5.25 blazar 3C446
Table 3: Candidate lenses in Revised IRAS FSC Redshift Catalogue
Figure 2: L: Star formation rate versus redshift for HerMES Lockman+XMM+ES1 galaxies, with 500 m selection limits for each template type. R: Star-formation rate versus redshift for extreme starbursts. Data from HerMES Lockman+XMM+ES1 (Rowan-Robinson et al 2016) and from the IRAS RIFSCz catalogue (Wang et al 2014). Known lenses are indicated by L and cases known to be unlensed indicated by U (Farrah et al 2002). Typical 60 and 500 m selection limits are indicated by the red and cyan loci.

3 Stellar mass, dust (and gas) mass, star formation rate

Our approach of fitting optical and near infrared SEDs with templates based on stellar synthesis codes (Rowan-Robinson et al 2010, Babbedge et al 2010) allows us to estimate stellar masses, and fitting mid infrared, far infrared and submillimetre data with templates based on radiative transfer models (Rowan-Robinson et al 2010, 2013, 2016), allows us to estimate star formation rates and dust masses. In this paper we particularly focus on the very highest rates of star-formation found.

In the automated fitting of infrared SED templates and calculation of infrared luminosities and other derived quantities, we previously normalised the SEDs at 8 m, if the source was detected there, or at 24 m otherwise. In studying the SEDs of galaxies with very high star-formation rates,we have found that normalisation at 8m for sources at z = 1.5-3.5 can result in poor estimates of the infrared luminosity, because for many sources with z 1.5 the 8 m emission is dominated by starlight. For z3.5 we already required normalisation to be at 24 m. We have therefore switched to normalisation at 24 m for all sources. We can do this for this sample because we require a 24 m detection in order to associate a Herschel source with a SWIRE photometric redshift catalogue source. This change significantly reduces the number of very high luminosity (and high star-formation rate) galaxies.

Figure 2L shows our revised plot of star-formation rate (SFR) against redshift for HerMES-SWIRE galaxies, which can be compared with Fig 2L of Rowan-Robinson et al (2016). Details of the revised HerMES-SWIRE catalogue are given at http:http:astro.ic.ac.ukpublicmrrspiresfr readmespirerev. These changes have some effect on the bright end of the star-formation rate functions (see appendix), but a negligible effect on the derived star-formation-rate density from z = 0-6.

Figure 2R shows the SFR against redshift for HerMES-SWIRE and RIFSCz galaxies with SFR . Typical IRAS 60 m and Herschel 500 m detection limits are indicated. The highest star-formation rates significantly exceed the highest rates found by Weedman and Houck (2008) at 0 z 2.5. There appears to be a natural upper limit to the SFR of 30,000 . No HerMES-SWIRE galaxies are found above this value and the IRAS-FSS galaxies above this limit are probably gravitational lenses (see previous section and Table 3). This limit could represent an Eddington-type radiation pressure limit on the star-formation rate of the kind postulated by Elmegreen (1983), Scoville et al (2001), and Murray et al (2005). Scoville et al (2001) give a limit for of 500 , which would translate to SFR for .

We can use the dust mass as a proxy for gas mass, assuming a representative value for . Magdis et al (2011) have summarised values of as a function of metallicity for local galaxies, and shown that a redshift 4 galaxy lies on the same relation, with (cf also Chen et al 2013). We use this ratio to estimate and then compare this with our stellar mass estimates. Figure 3L shows a plot of (100 versus redshift for HerMES galaxies. For HerMES galaxies with z1, is comparable with , so these are very gas-rich galaxies (as noted by Rowan-Robinson et al 2010). Very high gas fractions have been found in galaxies with z 1 by Daddi et ak (2010), Tacconi et al (2010, 2013), and Carrilli and Walter (2013). At low z, so these galaxies have consumed most of their gas in star-formation.

If we look at as a function of z (Fig 3R), we see that the time to double the stellar mass at z = 3-5 is yrs. In some objects the gas-depletion time is as low as 1-3x yrs (cf Rowan-Robinson 2000, Carilli and Walter 2013). The Scoville et al (2001) Eddington limit quoted above translates to yrs.

The picture that emerges is that the Herschel galaxies at z3 are in the process of making most of the stars in the galaxy. Essentially these are metal factories. However we are not seeing monolithic galaxy formation of the kind postulated by Partridge and Peebles (1967), even though the star-formation rates and time-scales are similar to those they suggested, because we can see from the optical and near infrared SEDs that there has been an earlier generation of star-formation at least 1 Gyr prior to the star-formation we are witnessing. Between z = 1 and the present epoch we see a dramatic decline in the gas content and star-formation rate. For z 0.5 the gas depletion time-scale is longer than the age of the universe so these are galaxies that must have had a much higher rate of star-formation in the past.

Figure 3: L: versus z. Circled points are extreme starbursts (SFR). R: (time-scale to make stars at present star-formation rate)versus z for HerMES galaxies, labelled with dominant infrared template type. Extreme starbursts (SFR ) are shown circled.

4 Extreme starbursts

Here we focus on galaxies with implied star-formation rates greater than 5000 . Previously, detailed studies have been presented of just two objects in this class: Rowan-Robinson and Wang (2010) show the SED of one unlensed RIFSCz galaxy in this class (IRAS F15307+3252, z = 0.926) with SFR = 5100 , and Dowell et al report an object (FLS1, z = 4.29) with SFR = 9700 .

We show modelling of individual SEDs for all HerMES-SWIRE (Lock+XMM+ES1) galaxies with SFR . There are 66 in all (details given in Tables 3 and 4), but SED modelling shows that 8 of these have low-redshift aliases which are more likely. Rowan-Robinson et al (2016) showed that fitting our starburst templates to the 250-350-500 m data gives an effective estimate of submillimetre redshift, . Combining the distributions for the photometric and submillimetre redshifts gives a best fit combined redshift . Values of and are given in Tables 3 and 4. For a further 7 sources, is significantly less than and we have shown the SED with above the corresponding SED for . For these 7 the alternative SED did not seem a better fit than that for . Generally the SED fits for the 58 sources are plausible. Only 3 are based on spectroscopic redshifts and it would be desirable to obtain further spectroscopy.

Fig 4L shows SEDs of objects whose optical and near infrared data is fitted with a QSO template. Pitchford et al (2016) have studied 513 Type 1 QSOs detected by Herschel at 250 m, some in the HerMES-SWIRE areas, and found star-formation rates ranging up to 5000 , so there is almost no overlap with our sample. Fig 5 shows SEDs of objects whose optical-nir data is fitted with a galaxy template, but whose mid ir data show the presence of an AGN dust torus, i.e. these are Type 2 AGN. Altogether 3058 objects are QSOs or Type 2 AGN. All of these have starburst components too and in no case does the luminosity in the AGN dust torus exceed that of the starburst.

Fig 6 shows SEDs of objects whose optical and near infrared data are fitted with galaxy templates and whose mid ir, far ir and submillimetre data are fitted with M82 or Arp220 starburst templates. Fig 4R shows galaxies whose mid and far infrared, and submillimetre, data are fitted with young starburst templates. Altogether 2858 objects are pure starbursts.

Star-formation rates in the range 5000-30,000 are not predicted by semi-analytic models of galaxy formation (Gruppioni et al 2015, Henriques et al 2015, Lacey et al 2016) and so these objects pose a serious challenge to theoretical models. Our 58 Herschel-SWIRE objects correspond to a surface density of 2.8 extreme starbursts per sq deg. 500 m sources which are not associated with SWIRE galaxies could add a further 9 extreme starbursts per sq deg.

Figure 4: SEDs of Lockman-SPIRE 500 m sources with extremes starburst luminosities labelled with the redshift, L: Optical-nearir fitted with QSO template. R: Farir-submm fitted with young starburst template. Lower redshift aliases () are shown with redshift bracketed, above SED for the higher redshift alias. Dotted loci: M82 starburst, dashed loci: Arp 220 starburst, long-dashed loci: AGN dust torus, red loci: young starburst template.
Figure 5: SEDs of Lockman-SPIRE 500 m sources with extremes starburst luminosities labelled with the redshift, midir requiring AGN dust torus template. Lower redshift aliases () are shown with redshift bracketed, above SED for the higher redshift alias. Dotted loci: M82 starburst, dashed loci: Arp 220 starburst, long-dashed loci: AGN dust torus, red loci: young starburst template.
Figure 6: SEDs of Lockman-SPIRE 500 m sources with extremes starburst luminosities labelled with the redshift, farir-submm fitted with M82 or A220 starburst templates. Lower redshift aliases () are shown with redshift bracketed, above SED for the higher redshift alias. Dotted loci: M82 starburst, dashed loci: Arp 220 starburst, long-dashed loci: AGN dust torus, red loci: young starburst template.
Figure 7: versus z for QSOs in SWIRE Photometric Redshift Catalogue. Solid black line corresponds to , for assumed optical bolometric correction of 2.0. Red line shows assumed dependence of dust torus covering factor on redshift.
Figure 8: L: Black-hole mass, , versus total stellar mass, , for HerMES-SWIRE sources and for RIFSCz sources with z0.3 (smaller points), with AGN dust tori. QSOs are excluded by the requirement that there be a stellar mass estimate, so these are all Type 2 AGN. Circled points are Herschel extreme starbursts. R: versus z for HerMES-SWIRE sources and for RIFSCz sources with z0.3, with AGN dust tori.
Figure 9: versus z for SWIRE and HerMES sources. Circled points are extreme starburst and blue open triangles denote QSOs.

5 Role of AGN

A surprisingly high proportion of Herschel extreme starbursts have an AGN dust torus component (52), though the dust tori are quite weak and in no case does exceed . Figure 7 shows the covering factor, versus redshift for SWIRE QSOs. Assuming the bolometric output of the black hole, (RR et al 2009), the average covering factor, f, is 0.4 for z2, declining to 0.16 at z = 0. This trend can also be interpreted as a decline in dust torus covering factor with declining optical (and bolometric) luminosity (see Rowan-Robinson et al 2009 and references quoted therein). Using this relation, Fig 8L shows black-hole mass, , versus total stellar mass, , for Herschel galaxies and for IRAS-FSS galaxies with z 0.3, where is estimated from assuming that the AGN is radiating at a fraction of the Eddington luminosity:

= 3.2 x (1)

is estimated as 2.0 for QSOs, and from for galaxies with AGN dust tori. A wide range of values of the Eddington ratio is found in the literature (Babic et al 2007, Fabian et al 2008, Steinhardt and Elvis 2009, Schutze and Wistotzki 2010, Suh et al 2015, Pitchford et al 2016), with a typical range of 0.01-1 for z 1 (Kelly et al 2010, Lusso et al 2012).

Since QSOs are excluded from fig 8L by the requirement for a measurement of stellar mass, these are all Type 2 AGN. The mean value of for 500 HerMES-SWIRE AGN is -4.11, with an rms dispersion of 0.56.

Figure 8R shows versus redshift for the same galaxies. If we take 0.1 as a characteristic value, then at all redshifts, with a range of 1 dex. This is reminiscent of the Magorrian et al (1998) relation between black-hole mass and bulge mass (see also review by Kormendy and Ho (2013). This ratio is set by the very high star-formation (and black-hole build-up) at redshift 2-5. The Milky Way, with and lies in the lower end of this range.

Figure 9 shows versus redshift for Herschel galaxies and for (non-Herschel) SWIRE galaxies (smaller symbols), where the black-hole accretion rate is calculated assuming conversion efficiency of accreting mass to radiation is =0.1:

. (2)

Note that the combination of equations (1) and (2) gives the Salpeter time-scale for black hole growth yrs (Salpeter 1964). QSOs have been indicated in Fig 9 by open blue triangles.

While is at z = 2-5, it is 30 times higher at z 0.5. The IRAS AGN (not shown) are consistent with low-z SWIRE galaxies. Barnett et al (2015) quote a much higher value of 0.2 for a redshift 7.1 QSO, based on a SFR derived from the CII 158 m line. However they also quote a bolometric luminosity of 6.7 x , which could yield a SFR of 13,000 , about 100 times their estimate from CII, and this would move into the range seen in Fig 9.

The star-formation rates in z0.5 galaxies are 1000 times lower than those seen in the extreme starbursts, but the black hole accretion rates are only 30 times lower. in these high redshift, high luminosity submillimetre galaxies we are presumably seeing major mergers (Chakrabarti et al 2008, Hopkins et al 2010, Haywards et al 2011, Ivison et al 2012, Aguirre et al 2013, Wiklind et al 2014, Chen et al 2015), in which the star formation is taking place close to the galactic nucleus, so it is not surprising that there is a strong connection between star-formation and black-hole growth. However at recent epochs star-formation is mainly fed by accretion from the cosmic web, by minor mergers and interactions, and by spiral density waves, so is taking place further from the galactic nucleus. This uncouples the direct connection between star-formation and black-hole growth. The gas feeding the black hole is fed to the galactic nucleus more gradually and may include gas fed by mass-loss from stars. It is still surprising that it is so much easier to feed a black hole at the present epoch than it is to form stars. Shallower evolution for AGN compared to that for starbursts was found for source-count models in which different types of object were allowed different rates of evolution (Rowan-Robinson 2009).

It is possible that the high proportion of AGN amongst these extreme starbursts is pointing to the influence of AGN-jet-induced star formation in these extreme objects (Klamer et al 2004, Clements et al 2009). The time-scales for these starbursts and the time-scale for black hole growth are remarkably well matched at a few x yrs (cf Rigopoulou et al 2009). However the greatly enhanced gas supply to the nucleus associated with violent mergers may be a sufficient explanation.

The SWIRE-Lockman area includes the CLASX X-ray survey and Rowan-Robinson et al (2009) gave a detailed discussion of the associations of CLASX and SWIRE sources. Only 2 of the 400 CLASX-SWIRE sources are detected by Herschel-SPIRE. While AGN are present in the Herschel submillimetre galaxy population, they make a negligible contribution to the submillimetre flux.

6 Conclusions

After careful exclusion of lensed galaxies and blazers, we have identified samples of extreme starbursts, with star-formation rates in the range 5000-30,000 , from the IRAS-FSS 60 m galaxy catalogue (RIFSCz) and from the Herschell-SWIRE (HerMES) 500 m survey. There do not seem to be any genuine cases with SFR30,000 and this may be essentially an Eddington-type limit. The SEDs of 58 HerMES extreme starbursts have been modelled in detail. The photometric redshifts are, in almost all cases, supported by redshift estimates from the 250-500 m colours. Using dust mass as a proxy for gas mass, extreme starbursts are found to be very gas rich systems, which will double their stellar mass in 0.3-3 x yrs.

About half of the Herschel extreme starburst systems also contain an AGN, but in no case do these dominate the bolometric output. With assumptions about the Eddington ratio and accretion efficiency, we find a universal relation between black-hole mass and total stellar mass, with . This is driven by the episode of extreme star-formation and black hole growth at z=2-5. But while the star formation rate has fallen by a factor of 1000 between redshift 5 and the present epoch, the black hole accretion rate has fallen by a factor of only 30, suggesting a decoupling between star formation and the feeding of the nuclear black hole.

7 Acknowledgements

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA).

References

  • (1) Aguirre P., Baker A.J., Menanteau F., Lutz D., Tacconi L., 2013, ApJ 768, 164
  • (2) Asboth V. et al, 2016, MNRAS 462, 1989
  • (3) Barnett R. et al, 2015, AA 575, A31
  • (4) Blain A.W., Smail I., Ivison R.J., Kneib J.-P., Frayer D.T., 2002,Phys.Reports 369, 111
  • (5) Chakrabarti S. et al, 2008, ApJ 688, 972
  • (6) Chen C. et al, 2015, ApJ 799, 194
  • (7) Chen B., Xinyu D., Kochanek C.S., Chartas G., 2013, astro-ph:1306.0008
  • (8) Clements D.L. et al, 2009, ApJ 698, L188
  • (9) Clements D.L. et al, 2010, AA 518, L8
  • (10) Daddi E. et al, 2010, ApJ 713, 686
  • (11) Dowell C.D. et al, 2014, ApJ 780, 75
  • (12) Elmegreen B.G., 1983, MNRAS 203, 1011
  • (13) Efstathiou A., Rowan-Robinson M., Siebenmorgen R., 2000, MNRAS 313, 734
  • (14) Efstathiou A., Rowan-Robinson M., 2003, MNRAS 343, 322
  • (15) Farrah D., Verma A., Oliver S., Rowan-Robinson M., McMahon R., 2002, MNRAS 329, 605
  • (16) Franceschini A. et al, 1991, AA Supp 89, 285
  • (17) Griffin M.J. et al, 2010, AA 518, L3
  • (18) Gruppioni C. et al, 2013, MNRAS 432, 23
  • (19) Gruppioni C. et al, 2015, MNRAS 451, 3419
  • (20) Hayward C. et al, 2011, ApJ 743, 159
  • (21) Henriques B.M.B., White S.D.M., Thomas P.A., Angule P., Guo Q., Lemson G., Springel V., Overzier R., 2015, MNRAS 451, 2663
  • (22) Hopkins P. et al, 2010, MNRAS 402, 1693
  • (23) Houck J.R. et al, 1985, ApJ 290, L5
  • (24) Ivison R.J. et al, 2012, MNRAS 425, 1320
  • (25) Kelly B.C., Vestergaard M., Fan X., Hopkins P., Hernquist L., Siemiginowska A., 2010, ApJ 719, 1315
  • (26) Kormendy J., Ho L.C., 2013, ARAA 51, 511
  • (27) Lacey C.G. et al, 2016, MNRAS 462, 3854
  • (28) Laigle C. et al, 2016, ApJS 224, 24
  • (29) Lapi A., Mancuso C., Celotti A., Danese L., 2017, ApJ 835, 37
  • (30) Magdis G.E. et al, 2011, ApJ 740, L14
  • (31) Madau P. and Dickinson M., 2014, ARAA 52, 415
  • (32) Magorrian J. et al, 1998, AJ 115, 2285
  • (33) Murray N., Quataert E, Thompson T.A., 2005, ApJ 618, 569
  • (34) Oliver S.J. et al, 2010, AA 518, L21
  • (35) Oliver S.J. et al, 2012, MNRAS 424, 1614
  • (36) Partridge R.B., Peebles P.J.E., 1967, ApJ 147, 868 Afonso-Luis A., 2013, MNRAS 428, 291
  • (37) Pearson W.J., Wang L., van der Tak F.F.S., Hurley P.D., Burgarella D., Oliver S.J., 2017, AA (in press)
  • (38) Pitchford L.K. et al, 2016, MNRAS 462, 4067
  • (39) Rigopoulou D. et al, 2009, MN 400, 1199
  • (40) Rodighiero G. et al, 2011, ApJ 739, 40L
  • (41) Rodighiero G. et al, 2014, MNRAS 443, 19
  • (42) Rowan-Robinson M. et al, 2008, MNRAS 386, 697
  • (43) Rowan-Robinson M. et al, 2010, MNRAS 409, 2
  • (44) Rowan-Robinson M. et al, 2013, MNRAS 428, 1958
  • (45) Rowan-Robinson M. et al, 2014, MNRAS 445, 3848
  • (46) Rowan-Robinson M. et al, 2016, MNRAS 461, 1100
  • (47) Rowan-Robinson M., Clements D.L., 2015, MNRAS 453, 2050
  • (48) Rowan-Robinson M., Valtchanov I., Nandra K., 2009, MN 397, 1326
  • (49) Rowan-Robinson M., Wang L., 2010, MNRAS 406, 720
  • (50) Rowan-Robinson M., Wang L., 2015, Publications of the Korean Astr. Soc. (in press), astro-ph 1505.03797
  • (51) Salpeter E.E., 1964, ApJ 140, 796
  • (52) Scoville N. et al, 2001, AJ 122, 3017
  • (53) Schulz B. et al, 2017, SPIRE Point Source Catalog Explanatory Supplement (IPAC, Caltech)
  • (54) Scoville N. et al, 2007, ApJS 172, 1
  • (55) Scoville N. et al, 2016, ApJ 820, 83
  • (56) Soifer B.T. et al, 1984, ApJ 283, L1
  • (57) Steinhardt C.L., Elvis M., 2009, MNRAS 402, 2637
  • (58) Tacconi L. et al, 2010, Nature 463, 781
  • (59) Tacconi L. et al, 2013, ApJ 768, 74
  • (60) Wang L., Rowan-Robinson M., 2010, MNRAS 401, 35
  • (61) Wang L. et al, 2014a, MNRAS 444, 2870
  • (62) Wang L., Rowan-Robinson M., Norberg P., Heinis S., Han J., 2014b, MNRAS 442, 2739
  • (63) Weedman D.W., Houck J.R., 2008, ApJ 686, 127
  • (64) Wiklind T. et al, 2014, ApJ 785, 111
Figure 10: Revised star-formation rate functions for z = 0.25-3.25, with 24 m normalisation.

Appendix A Appendix

Figure 10 shows the star-formation rate functions for z = 0.75-3.25 derived using the new 24 m normalisation (section 3 above). The tendency of the bright end of the function to be overestimated relative to the model fits (see Fig 9 of Rowan-Robinson et al 2016) has disappeared. The new parametric fits give star-formation rate densities that differ from the values of Rowan-Robinson et al (2016) by .

z = 0.75 1.25 1.75 2.25 2.75 3.25
old sfrd -1.28 -0.95 -1.06 -1.05 -0.82 -0.99
0.21 0.11 0.13 +0.27,-0.09 +0.18,-0.36 +0.29,-0.46
new sfrd -1.29 -1.05 -1.12 -0.97 -0.99 -0.92
Table 4: Star-formation rate density
RA dec i S24 S250 S350 S500 type SFR
(Jy) (mJy) (mJy) (mJy)
QSO Fig 4L
9.62462 -43.74844 R=17.45 11957 106.7 83.0 54.5 1.5670 QSO 2.9 9 2.40 2.39 4.02
164.96553 58.30081 19.44 5479.0 43.8 48.7 34.2 2.3350 QSO 13.6 11 2.33 3.47 3.94
36.84426 -5.31016 19.35 1963.8 52.7 45.4 36.7 3.07 QSO 42.1 14 3.01 3.07 3.80
164.64154 58.09799 20.95 1386.3 44.9 45.4 28.0 3.37 QSO 2.1 11 2.01 3.07 3.72
162.77605 58.52327 22.32 184.6 54.5 53.0 41.1 3.47 QSO 3.2 8 3.19 3.37 3.70
161.85410 57.91928 21.11 245.8 76.1 80.3 65.3 3.49 QSO 1.3 10 3.42 3.47 3.87
162.20728 58.28162 21.59 205.5 56.6 57.7 40.3 3.61 QSO 8.5 19 3.14 3.37 3.85
161.36092 58.03157 20.67 428.6 - 37.5 41.2 3.81 QSO 5.2 11 5.05 3.90 3.84
162.52769 57.28142 21.62 145.4 106.3 100.1 61.7 3.92 QSO 8.4 8 1.93 1.95 4.07
1.95 QSO 3.47
162.68120 57.55606 g=24.35 194.9 25.5 37.0 38.3 4.50 QSO 1.3 3 4.79 4.50 3.80
Type 2 AGN Fig 5L
33.71100 -4.17344 22.53 1016.3 96.2 69.0 32.5 1.47 Scd 9.3 6 1.92 1.57 3.82
8.04056 -43.71930 R=23.01 612.3 73.8 71.4 51.2 1.51 Sab 26.4 7 2.96 2.09 3.75
35.11776 -5.50099 23.55 864.4 72.2 65.1 45.2 1.55 Scd 9.0 7 2.74 2.02 3.78
162.91730 58.80596 22.03 1964.8 183.8 133.1 78.7 2.06 Sab 45.6 6 2.11 2.09 3.75
2 161.75087 59.01883 23.66 1329.6 75.0 61.0 40.6 2.5620 Scd 1.7 7 2.53 2.89 3.75
9.17274 -43.34398 R=23.65 2800.6 71.5 65.3 38.7 3.06 Sab 15.7 6 1.84 2.47 3.79
35.49809 -5.92264 23.57 1341.4 62.8 55.9 30.7 3.13 Sab 1.9 6 2.49 1.69 3.78
1.7 Sab 3.29
35.95578 -5.08144 23.85 1002.1 71.2 77.6 59.5 3.15 Sab 7.3 5 3.32 3.27 3.80
10.23271 -44.07592 R=21.50 487.0 75.3 68.1 45.7 3.29 sb 13.3 5 2.67 3.07 3.72
36.15258 -5.10250 24.92 627.2 43.5 53.7 41.5 3.37 Sab 2.0 5 3.60 3.47 3.71
162.38754 57.70547 g=24.13 519.3 65.7 65.0 56.3 3.37 Scd 1.6 3 3.47 3.37 3.74
159.78395 58.55888 g=24.41 231.6 35.3 39.9 36.7 3.72 Sdm 0.0 3 3.91 3.68 3.80
Fig 5R
163.98088 57.81277 g=24.66 213.9 27.8 34.6 41.0 3.74 Scd 4.4 5 5.03 3.68 3.79
36.96840 -5.02193 24.92 610.3 40.4 47.8 39.3 3.79 Sab 7.5 6 3.66 3.79 3.95
160.85139 58.02007 23.22 443.7 43.1 61.2 37.4 3.92 Sbc 2.6 5 2.24 3.37 3.93
35.11967 -5.73062 22.40 945.3 58.8 58.9 38.8 3.94 Sbc 14.8 6 2.90 1.69 3.83
35.92307 -4.73225 25.55 849.5 48.5 59.5 45.3 3.94 Sab 2.9 5 3.56 3.57 3.83
164.28366 58.43524 22.30 596.0 43.5 51.0 37.4 4.15 Scd 60.0 5 2.46 3.79 4.11
161.63013 59.17688 23.94 391.4 - 29.6 27.0 5.19 Scd 4.8 4 3.05 4.75 4.22
8.70199 -44.48560 R=25.38 423.0 31.2 36.1 27.1 4.73 Scd 0.01 3 3.45 3.47 4.23
9.30474 -43.03506 R=25.19 504.5 39.6 36.3 26.3 4.86 Scd 0.09 3 2.87 2.80 4.24
2.8 Scd 3.84
9.19681 -44.42382 R=24.35 249.1 39.2 43.2 41.0 5.00 sb (QSO?) 0.04 3 3.89 4.13 4.20
34.53469 -5.00769 23.47 342.8 47.3 42.4 35.8 4.40 sb 4.0 5 3.18 3.17 4.04
2.9
Table 5: Extreme starbursts: QSOs and Type 2 AGN
RA dec i S24 S250 S350 S500 type sfr
young sbs Fig 4R
159.03456 58.44533 21.37 1127.8 131.6 84.2 42.2 1.44 Scd 4.8 4 1.16 1.19 3.79
162.26817 58.46461 22.33 504.1 85.4 78.7 62.8 3.15 Sbc 5.0 6 3.16 3.17 3.87
160.33716 59.40493 22.36 1225.7 - 36.8 39.0 3.29 Scd 6.7 6 4.93 3.27 3.72
160.50839 58.67179 23.49 904.6 95.7 79.5 60.5 3.81 Sab 4.1 6 2.86 3.07 4.00
36.59817 -4.56164 25.11 389.5 59.3 67.2 54.7 3.88 Sab 2.1 5 3.53 3.68 3.83
36.10986 -4.45889 24.59 828.6 88.4 89.5 67.0 3.92 Sab 2.0 5 3.14 3.27 4.20
161.98271 58.07477 22.10 264.4 44.2 45.3 33.6 4.13 sb 25.4 6 3.15 3.68 3.76
M82, A220 Fig 6L
162.33324 58.10657 22.61 516.4 56.9 52.9 59.6 2.80 Scd 6.1 8 4.09 2.89 3.73
160.91940 57.91475 22.32 682.3 116.5 102.0 65.4 3.06 Sab 20.5 6 2.56 2.80 4.05
8.81979 -42.69724 R=22.90 706.2 87.4 74.6 53.9 3.19 Scd 6.1 5 2.72 2.98 3.72
161.21138 58.11261 23.29 560.2 148.6 116.4 54.2 3.33 Sbc 26.8 5 2.02 1.75 3.70
160.16505 57.27072 23.12 625.2 52.7 52.4 44.8 3.70 Sab 31.2 4 3.45 3.68 3.81
159.67438 58.55686 g=24.34 299.1 58.1 53.7 35.4 3.72 Scd 0.0 3 2.68 2.02 3.78
2.0 Scd 3.35
35.33492 -5.74307 24.94 799.9 69.9 74.9 45.5 3.81 Sbc 2.7 4 2.06 2.09 4.10
164.55716 58.65286 21.85 176.9 67.4 66.7 43.6 3.92 sb 2.3 6 2.96 3.57 4.04
159.95905 57.18814 g=24.01 232.5 - 36.5 37.9 3.37 Scd 0.1 3 4.88 3.37 3.73
162.84616 58.00514 g=24.41 179.3 34.4 40.1 32.4 4.01 sb 13.0 5 3.56 4.01 3.71
162.46065 58.11701 21.96 252.5 - 28.4 41.4 4.06 sb (QSO?) 7.9 6 4.81 4.13 3.88
Fig 6R
35.73369 -5.62305 23.42 422.0 73.1 60.9 42.1 4.11 Sbc 4.1 6 2.61 2.80 4.07
2.8 Sbc 3.77
7.98209 -43.29812 R=24.87 275.8 45.6 49.7 38.8 4.13 Sab 0.02 3 3.37 3.37 3.81
164.52054 58.30782 23.40 306.9 81.9 92.1 58.2 4.18 Sab 0.03 3 2.16 3.07 3.91
9.28433 -44.23750 R=25.06 437.0 62.5 72.5 51.5 4.18 Scd 0.03 3 2.40 2.39 3.95
161.89894 58.16401 23.60 315.0 66.4 59.7 35.3 4.37 Sab 22.7 4 1.82 2.89 3.96
35.73605 -4.88950 g=25.02 421.5 40.6 51.9 40.5 4.37 Scd 11.4 6 3.69 2.55 4.09
36.65871 -4.14628 24.91 288.8 46.1 45.7 48.1 4.40 Sbc 2.1 6 3.92 4.01 4.03
162.42290 57.18750 22.25 121.0 43.5 46.1 32.6 4.45 sb (QSO?) 5.6 4 3.22 4.37 3.74
161.58835 59.65826 23.71 156.0 48.1 35.1 31.8 5.05 Scd 4.7 5 3.03 2.98 4.07
3.0
preferred, SED not shown
159.24428 57.85775 22.68 281.7 85.7 64.4 27.3 3.06 Scd 3.1 5 1.80 1.51 3.72
162.55945 57.19608 22.12 315.3 74.6 56.8 26.9 3.70 sb 3.6 5 2.01 1.19 3.77
162.52769 57.28142 21.62 145.4 106.3 100.1 61.7 3.92 QSO 8.4 8 1.93 195 4.07
164.02647 52.07153 22.28 252.3 43.2 35.2 26.0 4.18 sb 2.5 4 2.74 1.82 3.71
9.08571 -45.59628 R=24.89 271.8 95.7 76.3 41.3 4.25 Scd 0.85 3 2.33 2.09 4.00
9.11142 -42.84052 R=24.44 354.5 37.6 45.0 30.1 4.60 Scd 0.03 3 2.36 2.31 3.95
34.26031 -4.95556 24.95 451.0 55.2 61.6 35.6 4.15 Sbc 3.9 4 2.03 21.6 4.05
36.25277 -5.59534 23.94 511.7 57.9 42.0 33.6 4.27 Scd 1.2 5 2.65 1.95 4.17
Table 6: Extreme starbursts: young starbursts, M82 and A220 type starbursts
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