Ionized gas kinematics of galaxies in the CALIFA survey I: Velocity fields, kinematic parameters of the dominant component, and presence of kinematically distinct gaseous systems
Key Words.:galaxies:evolution – galaxies: kinematics and dynamics – galaxies: star formation – galaxies: spiral – galaxies: elliptical – galaxies: irregular – techniques: spectroscopic
Context:Ionized gas kinematics provide important clues to the dynamical structure of galaxies and hold constraints to the processes driving their evolution.
Aims: This work provides an overall characterization of the kinematic behavior of the ionized gas of the galaxies included in the Calar Alto Legacy Integral field Area (CALIFA), offering kinematic clues to potential users of the CALIFA survey for including kinematical criteria in their selection of targets for specific studies. From the first 200 galaxies observed by CALIFA, we present the 2D kinematic view of the 177 galaxies satisfaying a gas content/detection threshold.
Methods:After removing the stellar contribution, we used the cross-correlation technique to obtain the radial velocity of the dominant gaseous component for different emission lines (namely, [O ii] , [O iii] , H+[N ii] , and [SII]). The main kinematic parameters measured on the plane of the sky were directly derived from the radial velocities with no assumptions on the internal prevailing motions. Evidence of the presence of several gaseous components with different kinematics were detected by using [O iii] emission line profiles.
Results:At the velocity resolution of CALIFA, most objects in the sample show regular velocity fields, although the ionized-gas kinematics are rarely consistent with simple coplanar circular motions. Thirty-five percent of the objects present evidence of a displacement between the photometric and kinematic centers larger than the original spaxel radii. Only 17% of the objects in the sample exhibit kinematic lopsidedness when comparing receding and approaching sides of the velocity fields, but most of them are interacting galaxies exhibiting nuclear activity (AGN or LINER). Early-type (E+S0) galaxies in the sample present clear photometric-kinematic misaligments. There is evidence of asymmetries in the emission line profiles in 117 out of the 177 analyzed galaxies, suggesting the presence of kinematically distinct gaseous components located at different distances from the nucleus. The kinematic decoupling between the dominant and secondary component/s suggested by the observed asymmetries in the profiles can be characterized by a limited set of parameters.
Conclusions:This work constitutes the first determination of the ionized gas kinematics of the galaxies observed in the CALIFA survey. The derived velocity fields, the reported kinematic distortions/peculiarities and the identification of the presence of several gaseous components in different regions of the objects might be used as additional criteria for selecting galaxies for specific studies.
Galaxies in the Local Universe are the result of billions of years of cosmic evolution. The study of their statistical and detailed properties are therefore expected to explain the evolution of galaxies. In particular, the analysis of the gas kinematics and their interplay with other galaxy components (essentially the stellar components) allows us to infer the dynamical structure of galaxies and to constrain the processes leading to their formation and evolution (see, e.g., López-Sánchez, 2010). These processes include the role of interactions during the galaxy lifetime (see, e.g., Méndez-Abreu et al., 2012, 2010; Aguerri et al., 2004), the relative mass contribution of luminous and dark matter (see Sofue & Rubin, 2001, for a review), the presence of supermassive black holes and their relationship with the large-scale properties of the host galaxies (see Merritt & Ferrarese, 2001, for a review), the origin of kinematically decoupled components (see Bertola & Corsini, 1999, for a review) and of disk heating (Merrifield et al., 2001, and references therein), the presence of pressure-supported ionized gas in bulges (Cinzano et al., 1999; Bertola et al., 1995), the fraction of quiescent and/or disturbed galaxies (e.g., Schawinski et al., 2010), or even the fraction of galaxies supported by rotation (e.g., Weiner et al., 2006).
The advent of integral field spectrographs made it possible for the first time to obtain 2D kinematics of the gas and stars and to overcome the difficulties associated with the interpretation of 1D velocity curves. The kinematics derived with the SAURON spectrograph (with a field of view of 33 x 41 arcsec) have been found to be rarely consistent with simple coplanar circular motions in early-type galaxies (Sarzi et al., 2006); in late types objects, gas and stars are decoupled in the inner central region (Ganda et al., 2006). The ATLAS 3D project (Cappellari et al., 2011), aimed at enlarging the sample, also uses SAURON. The DiskMass Survey (Bershady et al., 2010) uses the SparsePak (Bershady et al., 2004, 2005) and PPak (Verheijen et al., 2004; Kelz et al., 2006) integral field units with 1arcmin FoVs and jointly analyses gas and stellar kynematics for a sample of 30 nearly face-on spiral galaxies; among other results they report that galaxy disks are submaximal and that disks with a fainter central surface brightness in bluer and less luminous galaxies of later morphological types are kinematically colder with respect to their rotational velocities (Martinsson et al., 2013).
All these issues will greatly benefit from a survey like the Calar
Alto Legacy Integral Field Area survey
Studies based on gas kinematics, like the one presented in this paper (the stellar kinematics will be presented in a forthcoming paper by Falcón Barroso et al., in preparation), will be mainly devoted to the analysis of gas velocity fields, and provide a first estimation of the regularity of the assumed gravitational potential. For disk galaxies, departures from regular rotation can be easily traced, and asymmetries can be interpreted in terms
of the observed morphology. The importance of disk heating can be estimated by measuring the emission lines widths. Strong velocity gradients may be evidence of the presence of shocks; several line components will be eventual tracers of several kinematical components. This is the first of a series of works devoted to disentangling the ionized gas behavior through a comprehensive and homogeneous characterization of the main kinematic properties of the galaxies observed by the CALIFA survey. This work tries to promote the inclusion of kinematic criteria in the selection of galaxies from CALIFA survey for specific works.
The structure of this article is as follows. In Sect. 2, we summarize the observations, data reduction and main properties of the sample. In Sect. 3 we describe the procedure to derive the ionized gas velocity fields, the adopted methods to estimate some kinematic parameters directly from the observed radial velocities and the process to detect the presence of kinematically distinct gaseous components from the observed emission line profiles. In Sect. 4, we explore some dependences of the estimated kinematic indicators with galaxy types. Finally, a summary of the results is given in Sect. 5.
2 Observations and data reduction
2.1 CALIFA survey
The galaxies presented in this work are included in the CALIFA survey mother sample (S12), that comprises 939 galaxies selected from the SDSS DR7 (Abazajian et al., 2009). The main selection criteria to build this sample are the angular isophotal size (45 80, where is the isophotal diameter in the SDSS -band) and the proximity of these galaxies (0.005 0.03). These criteria are such that the selected objects represent a wide range of galactic properties such as morphological types, luminosities, stellar masses and colors. Further details on the selection criteria effects and a detailed characterization on the CALIFA mother sample are explained in S12 (see also Walcher et al., 2014). CALIFA has already released the first set of fully reduced, quality tested, and scientifically useful data cubes for 100 galaxies to the astronomical community (see Husemann et al., 2013, H13 hereafter). The data are available at http://califa.caha.es/DR1/ webpage.
2.2 Observations and data reduction
Detailed information of the observational strategy and data reduction are presented in both H13 and S12. In this section we summarize the most important aspects regarding the observational setup and data reduction of the CALIFA galaxies.
Observations were carried out using the PPak (PMAS fiber Package) fiber bundle (Kelz et al., 2006) of the Potsdam Multi-Aperture Spectrophotometer (Roth et al., 2005, PMAS) at the 3.5m telescope of the Calar Alto Observatory (Almería, Spain). Its main component consists of 331 fibers each with a diameter of 27, concentrated in a single hexagonal bundle covering a field-of-view of 74″64″, with a filling factor of 60% and a fiber-to-fiber pitch of 3.6 arcsec (Kelz et al., 2006). In order to cover the complete FoV and sample well the PSF, a dithering scheme of three pointings has been adopted.
The objects analyzed in this work have been observed in two spectral setups namely V500 and V1200. The V500 (V1200) setup has a nominal resolution of () at Å (at Å) and its nominal wavelength range is 3745–7300 Å (3400–4750 Å). The exposure time is fixed for all the observed objects. For the V500 setup a single exposure of 900 s per pointing of the dithering scheme is taken while for the V1200 setup 3 or 2 exposures of 600 s or 900 s, respectively, are obtained per pointing.
The data reduction is performed by a pipeline designed specifically for the CALIFA survey. The detailed reduction process is explained in S12, while improvements on this pipeline are presented in H13 (current pipeline version: V1.3c). The usual reduction tasks per pointing include cosmic rays rejection, optimal extraction, flexure correction, wavelength and flux calibration, and sky subtraction. Finally, all three pointing are combined using a flux-conserving inverse-distance weighting scheme (see S12 for details) to reconstruct a spatially resampled data cube, with a 1” sampling (see details in S12). The final FITS data cubes include science data, propagated error vectors, masks, and error weighting factors as described in H13.
2.3 The sample
The CALIFA project reached 200 galaxies observed with the two setups V500 and V1200 (see Sect. 2.2 and S12 for details on setups) in January 2013. From these 200 objects, we selected those galaxies with a minimum ionized gas contect/detection established as follows: detection of the H emission line with signal-to-noise (S/N hereafter) 20 (after stellar background subtraction) in at least the number of spaxels () subtending the effective angular resolution (3.7 arcsec, see H13) of the final 1 arcsec/pixel scale resampled data cube (S12). Given the large number of spaxels to analyse and the variety of profiles, the S/N of each emission line was just estimated from the peak of the line and the standard deviation of a region nearby to the emission line after the stellar continuum subtraction. We note that this quick estimation of S/N depends to first order on the spectral resolution. However, the adopted criterion is intended to select galaxies with blocks of contiguous spaxels to afford a kinematic view of the ionized gas, but any other ionized gas detection criteria could be adopted for specific studies (see, e.g., Papaderos et al., 2013; Singh et al., 2013). The number of objects satisfying the established minimum gas detection criterion is 177.
This sample of 177 objects spans all morphological types, as Fig. 1 shows; the morphological type was inferred by combining the independent visual classifications of several members of the CALIFA collaboration (see Walcher et al., 2014). Because of the CALIFA selection criteria (S12), a significant number (34%) of the galaxies in this sample have high inclinations (ellipticity 0.6). Inclinations were inferred from the outer regions of the SDSS r-band images of the galaxies in the sample using the standard task ellipse of IRAF
In Appendix A (Table 2), we list the galaxies in the sample together with their primary morphological characteristics, interaction/companion status and nuclear type obtained within the CALIFA collaboration. Table 2 also includes the systemic velocity and photometric major position angles of each object obtained from NED.
3 Measuring the ionized gas kinematics
The ionized-gas kinematics presented in this paper are measured from pure emission-line data cubes resulting from the subtraction of the best stellar continuum fit to the original CALIFA data (see some examples in Fig. 3). The bestfit stellar continuum is obtained as a product of the stellar kinematics analysis of the data as described in Falcón-Barroso et al. (in preparation). The wavelength range of CALIFA observations includes many bright emission lines (e.g., [O ii] for V1200 mode and H+[N ii] or [O iii] for V500 mode), which were masked during the fitting of the stellar continuum. The stellar kinematic results are not computed for each spaxel of the data cube, but on Voronoi bins (see Cappellari & Copin, 2003) ensuring a minimun signal-to-noise in the continuum of 20 per bin. Only spaxels with S/N 6 in the stellar continuum were used for binning (see details in Falcón-Barroso et al. in preparation). In order to extract the emission-line spectrum for each spaxel in the data cube, the individual spectra belonging to a given Voronoi bin were subtracted from the best stellar continuum fit for that bin. In the process we used a low order polynomial to ensure a flat continuum in the final emission-line data cube. Voronoi bins comes from the merging of a number of neighbouring spaxels in general not larger than the number of spaxels subtending the effective angular resolution of the data (except in the outer regions of the objects). Then, we do not expect strong variations of the stellar populations within each Voronoi bin.
3.1 Radial velocities
In order to obtain an integrated kinematic view of the ionized gas of the CALIFA galaxies, we have adopted the cross-correlation (CC hereafter) technique following the procedure proposed in García-Lorenzo (2013, GL13 hereafter). We note that the CC technique globally compares a problem spectrum with a reference spectrum, quantitatively measuring their similarities. This technique allows the dominant radial velocity of components integrated along the line of sight to be derived for systems with a variety of morphologies. Radial velocities are measured on the pure emission-line data cubes without adopting any optimal binning. We employ a Gaussian profile to model the upper part of the peak of the CC function. Estimated uncertainties in the location of the maximum of the CC function are km s from the covariance matrix of the standard errors in the fitting parameters for both V1200 and V500 configurations. Estimations of velocity dispersions for the ionized gas were also obtained from the full-width-half-maximum of the CC function for each spectrum at each selected spectral range. However, any analysis of velocity dispersions goes beyond the scope of this work.
The 2D distribution of ionized gas was obtained by integrating the signal in the spectral ranges selected to apply the CC technique. Noise in the selected spectral ranges affects the recovered emission line distributions and therefore these maps could slightly differ from those obtained by fitting Gaussians to emission lines in the spectra. Four spectral ranges (in rest-frame wavelength) including the bright emission lines [O ii] , [O iii] , H+[N ii] and [SII], were selected to infer the integrated ionized gas kinematics of the galaxies in our sample (see Table 1). The reference spectrum needed for the application of the CC technique was generated including as many Gaussians as single emission lines are expected in each spectral range selected to apply the technique (see Fig. 4). The noise contribution was not included in the templates to avoid degradation of the signal-to-noise ratio when the CC function is computed. The widths of the Gaussians were selected to be negligible compared to the problem spectra in order to keep the spectral resolution in the resultant CC function. The wavelength (or velocity) position of the required Gaussians to generate the template spectrum corresponds to the center of the emission lines at the redshift of the galaxies obtained from NED. Different weights (in flux) were given to the Gaussians to account for fixed intensity ratio between emission lines according to atomic parameters. Because CC technique also account for differences/similarities between reference and problem spectra, those parameters unfixed by atomic values could have an impact on the uncertainties when determining radial velocities. Integrating the signal in narrow band filters (two pixels wide) centered on emission lines, we estimated the intensity ratios of those emission lines not linked by atomic parameters. The typical intensity ratio adopted to generate the reference spectra are indicated in Table 1.
|CALIFA mode||Spectral range (Å)||Emission lines||Intensity ratio|
|V1200||3696-3759 Å||[O ii] +[O ii]||[O ii] /[O ii]|
|V500||4929-5037 Å||[O iii] +[O iii]||[O iii] /[O iii] =3|
|V500||6508-6623 Å||[N ii] +H+[N ii]||H/[N ii]|
|[N ii] /[N ii] =3|
Experiments using a set of different templates (with varying velocity, dispersion and relative intensity of the input Gaussians to generate the templates) were performed for the different selected spectral ranges to assess for the uncertainties due to template selection. The selection of unfixed intensity ratios, such as [O ii] or [S ii] , may have an important influence, increasing when lines are significantly blended (e.g., in the case of [O ii] ). To mitigate this limitation, we checked the average intensity ratios for each object in the sample, adapting the input ratio consequently. In same particular cases, the intensity ratios were even adapted in regions of a few spaxels. In general, the uncertanties associated with the template selection is km s; in the worst cases ([O ii] )), the selection of the template may contribute to increasing the radial velocity uncertainties up to 40 km s, but this is only the case for a few spaxels. However, it is important to point out here that these uncertainties refer to individual spaxels, while we are exploring global trends in the sense of coherent motions retrieved from hundreds of contiguous spaxels.
In order to assess for statistical uncertainties, we employed a Monte-Carlo simulation, deriving the different measurements from many realizations of the input data by adding the formal noise of the original data cubes (see H13 for error data cubes details). The procedure was repeated five hundred times, resulting in five hundred different input data cubes for each object in our sample. For each simulation we determined radial velocities only for those emission lines with an estimated S/N 6. In this way, we do not have the same final number of simulations per spectrum but we only consider those with a minimum number of estimations of one hundred, applying the Shapiro-Wilk test to check the normality of the distributions. Finally, we take the average as the measurement of the radial velocity. From the standard deviation we calculate the confidence interval at the 95% confidence level, which indicate the reliability of the measured radial velocities. In general, although these errors vary from spectrum to spectrum and from object to object, radial velocity measurements are accurate (95% confidence) to within 40 km s for [O ii], 15 km s for [O iii], 22 km s for H+[N ii], and 30 km s for [SII] (see the standard deviation 2D-distributions in Appendix C).
The error in the estimated radial velocity for each spectrum is actually a combination of the three previous sources of uncertainties: CC peak centroid, template selection and statistical uncertainty, being the last the dominant in most of the spectra.
The emission line profiles observed in galaxies arise mainly from one gaseous component, although the presence of different gaseous systems with different kinematics (as happens in the central region of galaxies with a certain degree of activity) can give rise to complex emission line profiles, showing blue/red wings, shoulders or double peaks (see, e.g., Wang et al., 2011, and references therein). These complex profiles are commonly identified by visual inspection and their analysis requires a kinematic deprojection in components (see, e.g., Arribas et al., 1996). Additionally, the CC function was also used to infer the presence of complex emission line profiles in the analyzed spectra by tracing line bisectors (see Sect. 3.3). Again the Monte-Carlo simulation approach is used to estimate statistical uncertainties in the calculation of bisectors. From the many realizations, we compute average bisectors for each spectrum and calculated their standard deviations at the different bisector levels. These standard deviations are then used to compute the confidence interval (95% confidence level) which is taken as uncertainties in tracing the bisectors. In general, bisector measurements are accurate within 20 km s (95% confidence) up to 40% bisector level (from the line peak to 40% of the peak intensity) for [O iii] emission line with a S/N10. For spectra with an estimated S/N20, the same accuracy is obtained for all the bisector levels.
3.2 Direct estimation of kinematic parameters
Most of our sample galaxies with extended emission line distributions show a global receding-approaching velocity field resembling that of rotating systems or, at least, ordered motions (see Appendix C). Nevertheless, departures from circular/ordered motions are evident in many objects in the form of clear kinematic distortions in the velocity fields. For the sake of uniformity in the analysis of the entire sample, a simple approach has been adopted to estimate the kinematic parameters observed in the plane of the sky directly from the measured radial velocities. Hence we avoid using any kinematical model or any assumption on internal dynamics or projection effects, and follow the procedures described in Sect.s 3.2.1, 3.2.2, and 3.2.3. The adopted approach allows a rapid determination of the frequency of kinematic distortions detected in the target galaxies in the plane of the sky. Kinematic models are being applied for specific studies within the CALIFA collaboration (see, e.g., Holmes, 2013).
Since enough gas is not always present, the distance from the center over which the kinematic parameters are estimated depends on each object, its surface brightness and its ionized gas content. Moreover, the reader should take into account that the sample includes many edge-on galaxies (ellipticity 0.6) and the estimation of the kinematic parameters for these objects are affected by projection effects or/and dust obscuration. Table 3 in appendix A includes the maximum radius (distance from the center) used to estimate the kinematic parameters for each galaxy. In general, the errors in the estimated parameters are taken as the standard deviation of the parameters in that distance range.
The bulk motion of a galaxy is provided by its systemic velocity, typically adopted as the radial velocity at the kinematic center. At the CALIFA spatial resolution (see S12 and H13), the photometric and dynamical centers should agree in position for most of the objects (see Sect. 3.2.2). Hence, the systemic velocity (V hereafter) for the objects in our sample have been estimated by averaging the radial velocities obtained in an aperture of 3.7 arcsec in radius (corresponding to twice the full-width-half-maximum of the CALIFA point-spread-function, see H13 for details) around the location of the optical nucleus (central spaxel of the data cube, see H13 for details). The systemic velocities were corrected from observed to heliocentric values using the correction in the header of each CALIFA data cube (see Table 4 in H13 for keyword). The standard deviation of the radial velocity measurements is taken as an indicator of the uncertainty in the determination of the systemic velocity. Large standard deviations indicate a large variation of the velocities in the central region of the objects. We note that the adopted aperture size corresponds to quite different physical sizes on objects at different redshifts. Indeed, an aperture of 3.7 arcsec on the galaxy at the lowest redshift in our sample (NGC~3057) corresponds to 376 parsec, while it covers almost 2.3 kpc for the largest redshift (NGC~6166NED01). Values of V have been obtained from [O ii] (V), [O iii] (V), H+[N ii] (V), and [SII] (V). In appendix A (Table 4) we list these values for each object. Only one galaxy (NGC~3158) has undetectable emission in the central 3.7 arcsec around the optical nucleus location. Indeed the emission in NGC~3158 (V=6989 km s from NED) is concentrated in a region arcsec northeast from its optical nucleus and could correspond to a small companion at 7171 km s.
For an ideal purely rotating disk galaxy, the rotation velocity varies with radius from the kinematic center, which coincides with the galactic center, and it is settled by the radial distribution of mass within the galaxy. The kinematic center of such a galaxy has a zero rotation velocity, and it is the location of the largest velocity gradient in the galaxy. Based on this idea and in order to estimate the location of the kinematic center (KC hereafter) of the sample galaxies, the average directional derivative of the H+[N ii] velocity field was computed by calculating the average absolute difference of the obtained velocity for each spectrum with the velocity of the surrounding regions. The resulting image (velocity gradient image hereafter) emphasizes those regions in the velocity field where the data are changing rapidly. Therefore, for galaxies showing regular motions, the peak of the average directional derivative image (velocity gradient peak hereafter) should indicate the KC (Kutdemir et al., 2008; Arribas et al., 1997). This procedure works quite well for regular velocity fields, with uncertainties smaller than the spaxel size. For complex kinematics, more than a single velocity gradient peak can arise in the gradient image, indicating several locations where radial velocities are changing rapidly. Indeed, in many cases the velocity gradient distribution shows the optical nucleus surrounded by a ring-like or a bar-like structure of large velocity gradient values. The presence of several velocity gradient peaks in the velocity field of a galaxy is then identified as a clear departure from pure rotation.
In order to estimate the position of the KC, a region of 1010 arcsec is selected around the largest velocity gradient peak. Then, we select those positions with a velocity gradient larger than the average velocity gradient inside this box. Finally, the KC is estimated from the weighted average location of the selected positions defining the peaks/structures of the velocity gradient map, using as weights the velocity gradient value at each location (see Fig. 5a, and 5b). Using the KC produces a more symmetric pseudo-rotation curve (see Sect. 3.2.3) than the optical nucleus or any of the locations with a large velocity gradient in the velocity field. This is the reason why we have adopted this procedure to estimate the location of the KC instead of just selecting the position of the largest velocity gradient in the maps. Uncertainties in the location of KCs are estimated assuming different radii — from the spaxel size to the PSF size (H13) — to define the surroundings of each spaxel when deriving the gradient images. Obviously, the detection of structures in the velocity gradient images is limited to the spatial resolution of the CALIFA data cubes.
Position angle of kinematic axes
The position angle of the kinematic major axis provides the mean orientation of the ionized gas velocity field. It is usually defined as the angle between the north and the receding side of the velocity field (e.g., Haan et al., 2009; Schoenmakers et al., 1997). For a rotating disk, the dependence of the kinematic major axis on galactocentric distance is negligible. The average orientation of the observed velocity fields (PA hereafter) can be directly estimated from the polar position of the spaxels defining the kinematic line of nodes (Nicholson et al., 1992; Bland et al., 1987) inferred as follows: (1) we plot the radial velocity of each spectrum/spaxel in a distance-velocity diagram, in which the origin (reference point) is taken as the KC position (see Appendices A and C); (2) we select those spectra/spaxels with the largest velocity differences and uncertainties smaller than the typical velocity error (22 km/s) with respect to V as a function of radius (see Fig. 6a,c), which trace the observed pseudo-rotation curve; (3) we locate the selected spaxels on the velocity field (see Fig. 6b,d) to trace the kinematic line of nodes; and (4) we average the polar coordinates (respect to the KC) of the selected spaxels to obtain PA. This simplistic approach to trace the kinematic major axis additionally allows us to determine the degree of symmetry of the velocity field by comparing mean position angle from the receding side (PA) with that from the approaching side (PA). In a similar way, we can estimate a mean position angle for the kinematic minor axis (PA hereafter) by selecting those spectra with the lowest velocity differences to V at any radius (see Fig. 6a,c) and locating them on the velocity field (see Fig. 6b,d). Only those spectra with a velocity difference smaller than the typical error for H+[N ii] velocities (22 km s) were considered to trace the PA. In a pure rotating disk galaxy, the kinematic minor and major axes are everywhere perpendicular (Binney & Merrifield, 1998). Therefore, the comparison of mean position angles for both axes also provides a parameter to account for kinematic distortions in the velocity field and departures from rotation.
For a rotating disk galaxy, this procedure traces the kinematic major and minor axes. For a distorted velocity field, the selected spaxels from the pseudo-rotation curve in the distance-velocity diagram may not be necessarily aligned and defining a clear direction on the velocity field. The reported position angles for kinematic major and minor axes in this work (see Table 3 in Appendix A) actually corresponds to the average of the polar coordinates of spaxels selected from the position-velocity diagram relative to the adopted KC (see Sect. 4.1.2). The standard deviation (PA hereafter) will provide the degree of alignment of these positions and then the agreement (or not) of the traced kinematic line of nodes with the classical idea of kinematic axis. It is important to note here that a rotating disk showing a variation of the inclination with galactocentric distance (tilted rings) will show a curved kinematic major axis, instead of a straight axis. Indeed, the axis curvature is related to the galactocentric variation of the disk inclination. The variation of PA as a function of a tilt follows the relation:
where [i] is the position angle of the major kinematic axis of a flat rotating disk that is seen at an angle i and [ii] is the corresponding position angle when the disk is tilted by i. For these rotating systems, the adopted PA approach will result in larger standard deviations than for flat disks. Following Eq. 1, a linear variation of 30 in i from the center to the outer parts of a tilted disk could increase the PA up to 20 for high inclined objects (i60). When i, PA will be smaller than 10 for a similar i galactocentric variation.
The accuracy in the estimation of the kinematic PA following the procedure described is a complex function of the actual position of the spatial elements of the CALIFA data cube set by the image reconstruction (see S12 for details), the uncertainties in determining the optical nucleus (taken at the data cube central spaxel, see H13 for details), the errors in the location of the KC, and the radial velocities uncertainties. As a reference, the accuracy in determining a defined position angle from a set of spatial elements in the CALIFA data cube is smaller than 0.5 degrees. Through the five hundred velocity fields for each object resulting from the Monte-Carlo simulations, we account for statistical uncertainties approaching the kinematic PAs. In general, PA and PA and their standard deviations are accurate (95% confidence) within 2 degrees. Regardless, the standard deviation of the positions averaged to estimate PA is taken as the uncertainty of this parameter.
3.3 Presence of kinematically distinct gaseous components
The presence of double/multiple gaseous components with different kinematics in galaxies is evident from the shape of the emission line profiles in their spectra, showing asymmetries, shoulders or double peaks. These features have been interpreted as due to rotating gaseous disks, outflows/inflows or dual active galactic nuclei (see, e.g., Fu et al., 2012, and references therein). The [O iii] line is usually selected to look for double/multiple gaseous components in the spectra of galaxies, since it is the brightest unblended emission line in the optical range for typical spectral resolutions (including CALIFA V500 data). Moreover, only faint stellar features are present in the [O iii] spectral region and hence, [O iii] is little affected by uncertainties in the subtraction of the stellar component, the opposite that in the case of e.g., H. A systematic search of double-peaked emission-line profiles can be done by tracing the bisector of a single emission line (e.g., [O iii] ) or the bisector of the CC peak function (obtained when comparing a problem spectrum with a reference created using a defined shape for the lines in the spectral range) and studying the shape of these bisectors, in particular the deviation from the central position/velocity for different bisector levels (GL13).
The spectral resolution of CALIFA is not the best to identify dynamically distinct gaseous components, but the identification of asymmetries in the emission line profiles will indicate where such multiple components may exist. It should also be noted that, because of the limited spatial resolution, beam-smearing of the velocity gradient could translate into non-Gaussian line structure. In any case, the strength of these asymmetries could have an impact when measuring emission line fluxes if these asymmetries are not taken into account (see Appendix B). The searching for asymmetries in the emission line profiles of the galaxies in the analyzed sample has been performed by analyzing the bisector shape of the CC peak function obtained when applying the CC technique to the [O iii] spectral range (from 4929 to 5036 Å in rest frame). The [O iii] spectral range was selected instead of the single [O iii] emission line profile to mitigate the influence of any observational or instrumental signature (e.g., cosmic ray) not properly removed during the data reduction process and affecting a single emission line, since the CC technique will smooth out these features providing an average profile shape. The reference spectrum (template) was generated following the procedure described in Sect. 3.1. It is important to note here that the level of noise in the problem spectrum affects the detection of asymmetries (the template is generated without noise). In appendix B we analyze the limits in the detection of double/multiple gaseous components in CALIFA V500 data cubes through a single-Gaussian model as a function of the signal-to-noise of the profile. Based on the results in appendix B, the searching of double/multiple gaseous components through the asymmetries in the [O iii] emission profiles should be restricted to observed spectra with an estimated S/N ([O iii] ) 30 and over a 10% intensity of the peak (10% bisector level). However, the Monte Carlo simulations in appendix B do not include the effects of the stellar subtraction that could be playing a role in the observed [O iii] profiles, mainly in those with lower S/N. To mitigate the impact of uncertainties in the stellar subtraction on the detection of multiple gaseous components, we only will consider those spectra with a minimum S/N of 40. We establish that a profile is actually asymmetric only when the absolute differences between the central velocity provided by the CC function and the velocity at two bisector levels (at least) are larger than the limits at each level established in Appendix B (equations 4 and 7).
Appendix A provides some structural parameters obtained from NED (V, and PA) and from measurements within the CALIFA collaboration (Table 2). Appendix A also includes the kinematic parameters (see Sect. 3.2) estimated from the H+[N ii] velocity field (kinematic center positions, velocities of kinematic center and position angles of kinematic axes) of each object in the sample (Table 3). The ionized gas velocity fields derived from [O ii] (V1200 mode), [O iii] , H+[N ii] , and [SII] (V500 mode) emission lines for the 177 galaxies with a minimum gas content/detection observed up to January 2013 in the CALIFA survey in both V1200 and V500 configurations are shown in Appendix C. In the following, we present the general kinematic properties of this sample.
4.1 Ionized gas distribution and velocity fields
For a general kinematic study of the ionized gas of galaxies in the CALIFA Survey, only spectra in the CALIFA data cubes with a S/N 6 in both the stellar continuum and ionized gas are considered (see Sect. 3). With these criteria, H+[N ii] emission is detected in at least 5% of the spatial elements (about 4420 in the resampled data cube, see S12 for details) on all galaxies in our sample. The simultaneous detection of [O ii], [O iii], H+[N ii], and [SII] emission lines was positive for 152 objects (86%). The galaxies in the sample show a large variety of ionized gas 2D distributions and, in general, their velocity fields show a global pattern of receding and approaching velocities (see appendix C).
The derived V and systemic velocities taken from NED (V hereafter) are in good agreement (see Fig. 7a). The weighted mean of V-V is 8.6 km s, using as weights the error bars in Fig. 7, which were derived from the standard deviation of the radial measurements and the published velocity uncertainties for V. For 175 of the 176 objects in the sample with H+[N ii] in the central region, the discrepancies between V and V can be attributed to differences in the procedures to determine them. Indeed, velocities in NED come not only from ionized gas but also from stellar or H i observations, velocities that can be significantly different. V could correspond to the velocity at the optical nucleus or to the brightest zone of each object, which could be far of the nucleus. Indeed, the large difference of 115 km s in V-V, corresponding to NGC~0160, is well explained if V comes from the brighter emission knots at the southwest of its nucleus. Only the derived V for NGC~6166NED01 presents a large discrepancy (larger than 1200 km s) with its V. The SDSS r-band image for this object shows several peaks and the center of the CALIFA data cube is located at the brightest, leaving the others at the southwest. These knots actually correspond to at least three objects: NGC~6166A at V=9271 km s; NGC~6166B at V=8104 km s; and NGC~6166C at V=9850 km s. At the southwest of the CALIFA data cube center, H+[N ii] velocities (with an average V of 9238 km s) are in agreement with the NED values for NGC~6166A. The average velocity of the brightest knot (CALIFA data cube center) is 8048 km s, in agreement with V for NGC~6166B.
According to the adopted signal-to-noise threshold, [O iii] emission is not detected in the central 3.7 arcsec of 15 galaxies (see Table 4 in Appendix A). For the remaining galaxies, V and V are in good agreement (see Fig. 7b), V-V = 2.2 24.8 km s. For nine objects, absolute differences range from 50 to 78 km s. The poor signal-to-noise of [O iii] emission lines in the central region of NGC~0499 (V-V km s), NGC~6063 (V-V km s), UGC~08234 (V-V km s), and UGC~08267 (V-V km s) could explain these differences. The discrepancies for the other five objects (NGC~6394, NGC~7466, UGC~03253, UGC~06036, and UGC~11717) could be associated with nuclear activity, as in the case of a broad line region affecting the permitted (H) emission lines and/or the presence of strong outflows producing double peaked profiles. Indeed, NGC~6394 and NGC~7466 are classified as Seyfert 2 galaxies (Véron-Cetty & Véron, 2010; Greenhill et al., 2009). We were unable to find published work on nuclear activity in UGC~03253, UGC~06036, or UGC~11717, although according to the emission-line diagnostic diagram for the most central spectrum (see Sect. 2.3), UGC~03253 is a star forming galaxy, while UGC~06036, and UGC~11717 are LINERS. Indeed, UGC~03253 and UGC~11717 have clear evidence of asymmetric [O iii] profiles in the central region (see Sect. 4.2), suggesting the presence of several gaseous systems.
Systemic velocities derived from [SII] (V) are also in good agreement with V values: V-V = -0.9 23.4 km s. We have omitted all objects with redshifts ranging from 5933 to 6588 km s in this comparison for which [SII] profiles are affected by a poor subtraction of the bright sky line at 6863.97 Å. No [SII] emission is detected in the central region of 21 objects (see Table 4 in Appendix A).
With the adopted S/N thresholds and using the V1200 data cube from CALIFA, [O ii] emission is not detected in the central region of 12 galaxies (see Table 4 in Appendix A). For the remaining objects, we found V-V 60 km s. Different elements contribute to this discrepancy: (1) the relative strengths of the [O ii] emission lines, with ratios ranging from 0.35 – for high electronic density regions – to 1.5 – for low electron density zones (e.g., Pradhan et al., 2006), and the strong blending of the two lines in almost all central spectra produce a large number of different [O ii] observed profiles. ; (2) [O ii] is more affected by dust obscuration than H+[N ii]; and (3) the subtraction of the stellar continuum under the [O ii] doublet is tricky because it is close to the blue border of the CALIFA V1200 spectral range. All these factors complicate the definition of an adequate template for the [O ii] spectral range (see Sect. 3), affecting the determination of the radial velocities.
Velocity gradients: estimating the location of the kinematic center
The 2D distribution of radial velocities derived from H+[N ii] spectral range allows the derivation of a velocity gradient image for most of the galaxies in the analyzed sample. As we already noted, the gradient image should present a clear peak at the KC for a purely rotating galactic disk. With this idea in mind, we have divided our set of galaxies according to the structures of the velocity gradient images: multiple peaks/structures can be due to different factors, including the presence of dynamically distinct components (e.g., a bar), whose study is beyond the scope of this work. We refer as Multi velocity Gradient Peak (MGP hereafter) to those galaxies showing several velocity gradient peaks or clear structures in the velocity gradient map. Single velocity Gradient Peak (SGP hereafter) indicates galaxies with a conspicuous velocity gradient peak, sometimes surrounded by faint structures or secondary peaks of much lower intensities. Galaxies in the SGP class should correspond to systems dominated by rotation, while MGP galaxies to objects presenting circular and non-circular motions at the velocity resolution of the CALIFA data. We lack a reliable velocity gradient map for a subset of 26 galaxies: (1) for 14 objects
The KC location was estimated from their velocity gradient images as explained in Sect. 3.2.2. Figure 8a shows the shifts between the derived KC position and the optical nucleus (ON hereafter) taken at the CALIFA data cube central spaxel (see H13). The ON was adopted as the KC for the UGP objects, and hence UGP galaxies are at the coordinate origin in Fig. 8a. We adopted the original spatial fiber size of the CALIFA survey (2.7 arcsec, see Sect. 2.2) as the minimum distance to report an offset between ON and KC. None of the SGP galaxies present ON-KC offsets larger than 2.7 arcsec (see Fig. 8a). For 10 MGP galaxies (see Table 3 in Appendix A) KC and ON are shifted a distance larger than 2.7 arcsec. 6 of these 10 objects are marked interacting galaxies (see Table 3 in Appendix A). A possible ON-KC offset is found for a subset of 52 galaxies of the sample (20 SGP and 32 MGP), with an ON-KC distance in the range between 1.35 arcsec (half of the original fiber size) and 2.7 arcsec. 22 of these objects (9 SGP and 13 MGP) were also identified as interacting systems (see Fig. 8b). At the CALIFA spatial resolution, ON and KC are in agreement for 47 SGP and 43 MGP galaxies.
Offsets between ON and KC are reported for many different galaxies [e.g., for local tadpole galaxies (Sánchez Almeida et al., 2013); for bulgeless disk galaxies (Neumayer et al., 2011); for Wolf-Rayet galaxies (López-Sánchez & Esteban, 2009); for dwarf elliptical galaxies (Binggeli et al., 2000); for AGN (Mediavilla & Arribas, 1993)]. Such offsets could be due to dust obscuration, which produce velocity fields and rotation curve gradients usually smoother than those for intermediate inclinations or almost face-on galaxies (Epinat et al., 2008). Offsets could be also due to actual displacement of a compact nucleus from the dynamical center (Miller & Smith, 1992; Levine & Sparke, 1998). The ionized gas is only a small fraction of the total mass of a galaxy, and it can be quite sensitive to non-axisymmetric perturbations (such as interactions, bars or feedback from massive stars) that could drive large ON-KC offsets. Indeed, nine of the ten galaxies in our sample with ON-KC distance 2.7 arcsec have weak/strong bars and/or interactions (either or both) and only one (IC~0776) seems to be a single and non-barred galaxy. IC~0776 is a peculiar late-type spiral galaxy displaying a large-scale asymmetry in its morphology. Its velocity field, at the CALIFA spectral and spatial resolutions, follows a general trend of receding and approaching velocities, with a quite distorted minor kinematic axis; its velocity gradient distribution (see Appendix C) is far from the expected single velocity gradient peak for a rotating system, suggesting that non-gravitational perturbations (may be warps and/or a minor merger) play a dominant role. For the galaxies (52 objects) with a possible ON-KC offset (ON-KC distance in the range 1.35-2.7 arcsec), 36 show signs of interaction and/or bars. The remaining 17 galaxies
The velocities derived for the KC (see Table 3 in Appendix A) are in good agreement with V, with V-V = 0 23 km s. Only three objects (namely, NGC~0169, NGC~3991, and UGC~03995) show a discrepancy larger than uncertainties. These galaxies present a large offset ( arcsec) between ON and KC.
Kinematic internal misalignment
We have traced the kinematic line of nodes and derived their mean PA and PA (see Sect. 3.2.3) for 166 of the galaxies in our CALIFA subsample. The H+[N ii] distribution extends arcsec (original spaxel diameter) or shows a patchy distribution in the remaining objects (see Table 3). The difference between PA and PA should be 180 degrees for a pure rotating disk system but, for many of the objects in the sample, this difference is far from this value. The misalignment of these two approaches of the mean position angle of the kinematic major axis is given by:
with in the range between 0 and 90 degrees (Franx et al., 1991). We adopt to define a kinematic lopsidedness in terms of the major kinematic axis. A similar limit was previously used to report misalignments between the photometric and kinematic axes in spiral (Kutdemir et al., 2008) and early-type galaxies (Krajnović et al., 2011). Almost 82% of the objects with estimation present internal kinematic misalignments smaller than 10 (% of the objects in the full sample). Only 30 galaxies show along the major pseudo-axis from the receding to the approaching sides of the velocity fields, reaching a maximum value at around 65 for ARP 220 (see Fig. 9a).
During a major merger, complex kinematics could arise as a result of the tidal forces (e.g., Kronberger et al., 2007; Rampazzo et al., 2005). The full analyzed sample (177 galaxies) includes 71 objects (%) identified as interacting galaxies (see Sect. 2.3). Only 21 of these systems present a clear internal asymmetry in the velocity fields ( 10). The rest of the objects showing are apparently isolated galaxies. The degree of symmetry of a velocity field may also be affected by the presence of dust lanes, spiral arms, bars, warps, outflows/inflows, shocks or nuclear activity, minor mergers or enven interactions with difuse objects (see, e.g., Fridman et al., 2005; Fathi et al., 2005; Wong et al., 2004; López-Sánchez, 2010). Their kinematics imprints could range from km s (Wong et al., 2004, for radial inflows, see) to a few hundred of km s (for outflows from an AGN, see, e.g., Arribas et al., 1996)). Small-scale perturbations (in the spatial and/or velocity spaces) are smoothed or even undetectable depending on the spatial and spectral resolution of the observations. At the resolution of CALIFA V500 data cubes (see Sect. 2.2), we find a similar proportion of galaxies with kinematic misalignments in barred and unbarred galaxies (see Fig. 9b). The proportion of kinematic lopsided in terms of () seems to be slightly larger for interacting galaxies (21/61) than for AGN/LINER galaxies (15/63). However, the 5 objects with are AGN/LINERs, and 4 of them are galaxies in interaction. Moreover, it is important to highlight that 12 of the 15 AGN/LINER objects with are also classified as interacting/merger galaxies. This proportion is much larger than those AGN/LINER galaxies in interaction with (16/48).
As already mentioned (see Sect. 3.2.3) the standard deviation (PA hereafter) of the positions used to estimate the kinematic major axis indicates the degree of their alignment on the velocity field and their correspondence or not with a straight kinematic line of nodes (a negligible dependence on galactocentric distance of the major kinematic axis). The larger the PA is the larger departure for pure rotation. Fig. 9c shows the largest PA (maximum PA at receding and approaching sides of the velocity field) for each galaxy as a function of morphological ellipticity. We note that we are estimating kinematic parameters on the plane of the sky plane (directly from observed radial velocities) and PA should show a dependence like in equation 1. Figure 9c includes PA curves as a function of ellipticity for selected PA at face-on. Many objects (mainly edge-on) present much larger PA than expected, may due to the presence of dust lanes, warps, outflows/inflows inducing apparent or real vertical motions. UGC~10650 is the object presenting the largest PA (in its approaching side). UGC~10650 seems to be an edge-on galaxy with a similar appearance to tadpole objects. At the spatial and spectral resolution of CALIFA, UGC~10650 shows a quite chaotic velocity field, not compatible with simple rotation (see Appendix C). On the other side, the face-on galaxy NGC~2347 presents the lowest PA values (at the receding and approaching sides), suggesting that rotation is the dominant motion. Indeed, in terms of PA, NGC~2347 seems to be the most symmetrical of the face-on galaxies in our sample.
Almost 42% of the studied objects present PA (at the receding and/or approaching sides) larger than 15 degrees (see Fig. 9d), while % have PAs larger than 30 degrees. 45% of the objects with PA larger than 15 degrees are apparently isolated galaxies (31/69), but 22 of them present a bar or/and nuclear activity. Half of the remaining isolated galaxies with PA are edge-on and vertical motions in the disks and/or dust obscuration could be the responsible of the observed kinematic distortions. Poor gas content, the presence of hidden bars or a past interaction with a satellite object could explain the kinematic distortions of the other half non-barred isolated galaxies showing PAs larger than .
The orthogonality of the kinematic pseudo-axes also provides an approach to the distortions in a velocity field. Figure 10a shows the difference respect to normal ( hereafter) calculated from the average kinematic minor and major PA through:
We took the average of PA and PA as PA in this equation. We only estimated the kinematic minor axis for a reduced number of objects (93 galaxies) because of the limited extent of the ionized gas along this direction (mainly galaxies with ellipticity larger than 0.6). % of the galaxies (65 of 93) in this subsample have , while only 10 (of 93) deviate from normality more than 20 (see Fig. 10a and b). 75% (21 of 28) of the objects with are barred galaxies, 12 of them also have an AGN/LINER type nuclear spectrum and even 9 of them show signatures of interactions. Only NGC~7819 shows being an apparently isolated and unbarred galaxy with a nuclear spectrum compatible with star formation (see H13). An additional indicator of large distortions in the minor kinematic axis is the standard deviation of the angles averaged to estimate PA (PA hereafter). % of the objects (58 of 93) present PA. Only 6 of 93 galaxies have PA, identified the 6 as interacting galaxies with nuclear activity (AGN/LINER).
Photometric to kinematic pseudo-axes mislignment
The photometric position angles of the galaxies in the sample were obtained from NED (PA hereafter). Most of PA correspond to estimations from K images from 2MASS, but some of the PA comes from other sources (see NED). The average of PA and PA (see Sect. 4.1.4) is taken as the orientation of the velocity fields (PA). Following equation 2, we estimated the misalignment ( hereafter) between photometric (PA) and kinematics (PA) maps orientations. Figure 11b shows the histogram of for 162 objects in our sample (those with both PA and PA values). 57% of the objects (93/162) are in the first two bins (), while 21% of the galaxies (34/162) present , with the maximum misalignment reaching 87 for UGC~11649. The visual inspection of UGC~11649 broad band images reveals a strong bar crossing the galaxy and almost perpendicular to the apparent rotation axis of its velocity field (see appendix C). Indeed, 45 of the 69 objects with are barred galaxies, and half of the objects with have strong bars (see Fig. 11b). We find an excess of early-type galaxies with photometric-kinematic misalignments, with 9 of the 10 ellipticals and S0 galaxies in this subsample showing (for 6 of them ). The largest misaligment for the early-type galaxies corresponds to NGC~7671 (), morphologically classified as an S0 galaxy and forming a pair with NGC~7672 (placed at kpc from NGC~7671 and with a difference in systemic velocity of km/s). It is important to note that 8 of the 10 early-types (E+S0) galaxies in this subsample of 163 objects are involved in dynamical interactions (according to the established criteria in Sect. 2.3), and 9 show a LINER type nuclear spectrum. It is also important to point out that most of the early-type galaxies in the sample have a limited extent of ionized gas ( arcsec).
For a homogeneous dataset of photometric position angles, we fitted the isophotes of the SDSS r-band images of the galaxies in the sample by ellipses using the standard IRAF task ellipse (Jedrzejewski, 1987), deriving the radial variation of photometric position angles and ellipticities. We defined an external photometric position angle (PA hereafter) by averaging the outer isophotes. PA represents the global stellar structure but could be affected by close companions. We also calculated the morphological position angle at one effective radius for each galaxy (PA hereafter), which can account for internal morphological structures such as bars. PA and PA are listed in Appendix A (Table 2). These two approaches of the photometric position angles are also used in Falcón-Barroso et al. (in preparation) for the statistical analysis of the stellar kinematics of a sample of CALIFA galaxies and in Barrera-Ballesteros et al. (in preparation) for the comparison of stellar and ionized gas kinematic for a sample of interacting galaxies following a merging sequence. Figure 11 shows the comparison of these photometric position angles with the orientation of the velocity fields following equation 2.
Similar statistical results are obtained when comparing PA and PA ( hereafter) to those obtained for . We have an excess of barred galaxies (48 of 78) with and also an excess of early-type galaxies with large misaligments (8 of 10). Moreover, 18 of the 28 objects in interaction with nuclear activity (AGN or LINER) present inner morpho-kinematic misaliments (). On the other hand, the misalignment between kinematics and PA ( hereafter) is quite small for a large number of objects in the sample (see Fig. 11e and 11f): 129 of 162 objects ( %) have , and in total 89% of galaxies present (in agreement with results in Krajnović et al. (2011) for early-type galaxies). is larger than for only 14 of the galaxies with a weak/strong bar (% of the barred galaxies in the sample). Otherwise, 19 of the 33 galaxies with present some degree of nuclear activity (31% of the AGN+LINER objects in the sample), while 23 of the objects with are identified as interactions (% of the interacting galaxies in the sample), 14 of them having also nuclear activity. Indeed, half of the galaxies with nuclear activity and in interaction show . Again, the largest excess of galaxies showing photometric and kinematic misalignments correspond to early-type objects (E+S0), with 7 of the 10 early-type galaxies in the sample having . However, we note that all the objects with strong morpho-kinematic misaligments () are interacting galaxies (see Fig. 11f). Barrera-Ballesteros et al. (in preparation) study the morpho-kinematic misaligments (as well as the stellar-ionized gas kinematic misaligments) for a sample of interacting galaxies.
4.2 Presence of kinematically distinct gaseous components
The presence of asymmetries in the observed spectra can be studied for 122 galaxies, % of the galaxies in the analyzed sample, those satisfying the signal-to-noise threshold (S/N in [O iii] , see Sect. 3.3). Obviously, the total number of spectra with estimated S/N larger than 40 varies from object to object, from a minimum of three to more than thousand spatial elements of the CALIFA data cubes. We assume three contiguous spectra as the minimum number of spaxels to define a region.
Asymmetries are detected in 117 objects at different bisector levels with absolute velocity shifts respect to a Gaussian bisector (V) larger than the limits estimated in Appendix B (F(S/N), equations 4 and 7) for noise induced asymmetries in CALIFA profiles. We classified the detected asymmetries into three categories according to the number of bisector levels at which the profiles appear asymmetric:
Class A: V is larger than F(S/N) in more than five bisector levels. In general, class A profiles correspond to asymmetries first detected over a 30% of the peak intensity level.
Class B: V is larger than F(S/N) in a number of bisector levels between 3 and 5. Frequently, class B profiles correspond to asymmetries first detected at intensity levels between 20% and 30% of the intensity peak.
Class C: V is larger than F(S/N) only in two bisector levels. Commonly, class C corresponds to profiles with asymmetries in the 10% and 15% bisector levels.
Moreover, we can classify the detected asymmetries according to the maximum deviation of the bisector from a Gaussian (V), adopting the following types:
Type 0: max(VF(S/N) F(S/N) km/s
Type 1: F(S/N) max(VF(S/N) F(S/N)
Type 2: max(VF(S/N) F(S/N) km/s
Following these divisions, we have nine different categories of asymmetries in the profiles (namely, A0, A1, A2, B0, B1, B2, and C0, C1, and C2) depending on the bisector velocity deviation from a Gaussian and bisector level at which the asymmetry is first detected. In appendix B, we explored the parameter space of two kinematically distinct gaseous components producing asymmetric emission profiles, founding that classes and types result from a complex combination of the parameters (velocity, velocity dispersion and intensity) of each gaseous component contributing to a particular emission line profile.
Class C profiles are found in the spectra of 108 objects. In 79% of the objects (92 of 117), we detect class B profiles, while only 25 galaxies have class A profiles. Obviously, a single galaxy can present spectra of different asymmetry classes depending on the kinematics of the gaseous systems from region to region. Table 4 in Appendix A indicates the classes and types of asymmetric profiles detected for the different galaxies. The presence of several gaseous components in the rest of the objects of our sample and/or at additional spectra cannot be ruled out, but we are not able to detect them at the resolution and depth of the CALIFA data cubes. These two facts could also be masking any trend on the presence of multiple gaseous systems with galaxy types. Indeed, asymmetric emission line profiles are found in spiral galaxies but also in elliptical galaxies. We stress that most elliptical galaxies in the sample do not satisfy the signal-to-noise threshold to look for asymmetries. Neither the interaction with a nearby galaxy nor the presence or absence of a bar (strong or weak) seems to be associated with the detection of asymmetries in the emission line profiles of the galaxies in the sample.
Asymmetries in the [O iii] profiles are found in regions around the nuclear zone (up to 2 kpc), in compact regions out of the nuclear zone but also in dispersed regions all over the galaxies. Figure 12 presents the distribution of profiles according to the detected asymmetry class, indicating the fraction of them located at different distances from the galaxy center. Although all categories of asymmetries in the profiles are found at different scales in the analyzed objects, in general asymmetries in the emission line profiles for spectra coming from the central regions suggest brighter secondary components with respect to the dominant than the secondary features for spectra in the outer regions of the galaxies. Moreover, the difference in velocity between the dominant and the secondary components seems to be also larger for spectra in the central region than those in the outer parts. However, from a model of two Gaussian (see Appendix B) we found that many combinations of the parameters characterizing each component can result in an specific class and/or type asymmetric profile. Commonly, asymmetric emission line profiles detected out of the circumnuclear region are generally in clouds surrounding bright emission knots and/or at bright emission regions. At the spatial resolution of the CALIFA survey many of the emission knots could lumps of unresolved emission knots.
Complex emission line profiles in the central region of galaxies have been commonly interpreted as bi-polar outflows driven by starbursts or AGN radiation pressure (Shen et al., 2011; Monreal-Ibero et al., 2010; Heckman et al., 1981, see, e.g.,). Multicomponent emission line profiles are also observed in many luminous H ii regions associated with the expansion of bubbles produced by stellar winds from massive stars (e.g., Rozas et al., 2007; López-Sánchez et al., 2007). Luminous H ii regions emission line profiles are characterized by a central peak and one or two high velocity features that could be associated with the asymmetries detected in the CALIFA [O iii] profiles according to the observed velocity shifts (see, e.g., Relaño et al., 2005). Multiple massive star-forming clumps have been also suggested as the origin of complex profiles in dynamically young host galaxies (Amorín et al., 2012). The presence of a nearby galaxy or a small satellite companion (in interaction or not) could also explain the observation of complex emission line profiles depending on the orientation respect to our line of sight. Even in absence of kinematically distinct gaseous components, complex emission line profiles could result from beam-smearing of the velocity gradients within the observation aperture. A detailed analysis of the origin of asymmetric emission line profiles for each galaxy in our sample is far from the scope of this work but could be the issue of a future dedicated work. The main intention here is to indicate the presence of multiple gaseous systems in the objects to users of the CALIFA database. As we already mention, the presence of secondary gaseous systems could give rise to complex emission lines, and such deviation from a Gaussian profile could have an impact on the calculation of parameters from emission line fluxes (see Appendix B).
5 Summary and conclusions
In this paper we present a basic analysis of the ionized gas kinematics of the galaxies in CALIFA. Our main results and conclusions are summarized by the following items.
At the spatial and spectral resolution of CALIFA, the ionized gas velocity fields of the galaxies in the sample present, in general, the typical pattern of receding and approaching velocities.
Systemic velocities derived from different emission lines are in good agreement and they are compatible (within uncertainties) to values in NED.
Almost half of the galaxies in the sample have clear structures in the velocity gradient maps, indicating clear departures from rotation at the resolution of CALIFA.
We find evidence of displacements between the photometric and kinematic centers for 35% of the objects in the sample. The largest offsets mainly correspond to galaxies in interaction.
The major kinematic position angles estimated from the receding and approaching sides of the velocity fields suggest a kinematic lopsided in 17% of the galaxies in the sample. A significant fraction of these galaxies correspond to interacting objects with nuclear activity (AGN or LINER).
Deviations larger than 15 in tracing the major kinematic axes are found in almost 40% of the analyzed objects, indicating clear departures from pure rotation.
Deviations () from the normal between the minor and major kinematic axes are mainly associated with the presence of a bar in the objects .
We find an excess of early-type galaxies (E+S0) showing photometric-kinematic misaligments.
Evidence of the presence of kinematically distinct gaseous systems are found in 69% of the galaxies in the sample.
Acknowledgements.This study makes uses of the data provided by the Calar Alto Legacy Integral Field Area (CALIFA) survey (http://www.califa.caha.es). Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). CALIFA is the first legacy survey being performed at Calar Alto. The CALIFA collaboration would like to thank the IAA-CSIC and MPIA-MPG as major partners of the observatory, and CAHA itself, for the unique access to telescope time and support in manpower and infrastructures. The CALIFA collaboration thanks also the CAHA staff for the dedication to this project. We thank the Viabilidad, Diseño , Acceso y Mejora funding program (ICTS-2009-10) for supporting the initial developement of this project. B.G-L and J.B-B thank the support from the Plan Nacional de I+D+i (PNAYA) funding programs (AYA2012- 39408-C02-02) of the Spanish Ministerio de Economía y Competitividad (MINECO). I.M., J.M. and A. d.O. acknowledge financial support from the Spanish grant AYA2010-15169 and Junta de Andalucia TIC114 and Excellence Project P08-TIC-03531. S.F.S. and D. Mast also thank the support given to this project from the PNAYA of the MINECO under grant AYA2012-31935. S.F.S thanks the the Ramón y Cajal project (RyC-2011-07590) of the Spanish MINECO, for the support giving to this project. JMA acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild). We acknowledge financial support for the ESTALLIDOS collaboration by the Spanish MINECO under grant AYA2010- 21887-C04-03. J. F.-B. acknowledges financial support from the Ramón y Cajal Program and grant AYA2010-21322-C03-02 from the MINECO, as well as to the DAGAL network from the People Programme (Marie Curie Actions) of the European Unionâs Seventh Framework Programme FP7/2007-2013/ under REA grant agreement number PITN-GA-2011-289313. KS acknowledges support from the National Sciences and Engineering Research Council of Canada. A. M.-I. acknowledges support from Agence Nationale de la Recherche through the STILISM project (ANR-12-BS05-0016-02) and from BMBF through the Erasmus-F project (grant number 05 A12BA1). P.P. is supported by Ciencia 2008 Contract, funded by FCT/MCTES (Portugal) and POPH/FSE (EC), and JMG by a Post-Doctoral grant, funded by FCT/MCTES (Portugal) and POPH/FSE (EC). PP&JMG acknowledge support by the Fundação para a Ciência e a Tecnologia (FCT) under project FCOMP-01-0124-FEDER-029170 (Reference FCT PTDC/FIS-AST/3214/2012), funded by FCT-MEC (PIDDAC) and FEDER (COMPETE). R.A. Marino was also funded by the Spanish programme of International Campus of Excellence Moncloa (CEI). Finally, we are grateful to the referee, Matt Bershady, for a careful reading of the paper and his several comments that helped to improve this paper.
Appendix A Tables
In this appendix, we summaryze the main photometric parameters of the galaxies in the sample (Table 2) obtained (within the CALIFA collaboration) from SDSS r-band images of the galaxies in the sample (see Walcher et al. 2013, in preparation for details). In Table 2 columns correspond to:
Columns  and : Object and CALIFA unique ID number for the galaxy, respectively.
Columns  and : Systemic velocity and position angle of the apparent major axis obtained from NED.
Columns : Effective radius in arcsec of the disk estimated as detailed in Sánchez et al. (2014) .
Columns : Radial distance (in units of the effective radii) used to estimate the large-scale photometric position angles (in column 8) and ellipticities (in column 9).
Columns  and : Morphological position angles at one effective radius (PA) and at the largest scale of the SDSS images (PA). Both measurements were inferred from the SDSS r-band image of the galaxy using the IRAF task ellipse.
Column : Ellipticity of the outer isophotes of the SDSS r-band image obtained using the IRAF task ellipse.
Column : Identification of the galaxy as isolated (I G), interacting/merging (IoM G), or group of galaxies (GoG) (see Section 2.3 for criteria on this division). Here, we divide the interacting sample analyse in the work (pair of galaxies, small groups of galaxies and mergers with tidal features) in IoM G and GoG just for reference to future works.
Column : Morphological type from visual classification performed by the CALIFA collaboration (see H13 and Walcher at al. 2013, in preparation for details).
Column : Bar strength of the galaxy as an additional outcome of the CALIFA visual classification (see H13 and Walcher at al. 2013, in preparation for details). We divided the galaxies into non-barred (A), weakly barred (AB) and strongly barred (B).
Column : Nuclear type of the object indicating the main ionization mechanisms in the central region determined through diagnostic diagrams (see Section 2.3). SF, LINERS and AGN indicate pure star formation, low-ionization nuclear emission-line regions and active galactic nuclei, respectively. INDEF indicates that the nuclear type could not be inferred (see Section 2.3).
In Table 3 we include the kinematic parameters directly derived from the measured radial velocities of the H+[N ii] emission lines for each galaxy. Each column corresponds to:
Column : CALIFA ID number for the galaxy.
Column : Classification of the galaxy according to the structures in the velocity gradient map obtained from the H+[N ii] velocity field. SGP, MGP, and UGP indicate Single, Multi and Unclear velocity Gradient Peak (see Section 4.1.2).
Columns  and : Position (in arcsec) of the kinematic center (right ascension , and declination ) relative to the central spaxel of the CALIFA data cube (see Table 4 in H13 for keyword) (see Section 3.2.2).
Column : Average velocity (in km/s) in an aperture of 3.7 arcsec in radius centered at the location of the kinematic center. Errors correspond to the standard deviation of the average radial velocities.
Columns  and : Position angle of the major kinematic pseudo-axis estimated from the receding () and approaching () sides of the velocity field and taking the reference position at the kinematic center. Errors correspond to the standard deviation of the polar coordinates of the spaxels tracing these axes (see Section 3.2.3).
Column : Position angle of the minor kinematic pseudo-axis. Errors correspond to the standard deviation of the polar coordinates tracing this axis (see Section 3.2.3).
Table 4 includes the systemic velocities derived from different emission lines through a 3.5 arcsec aperture in radius on the zero reference spaxel (galactic nucleus) of each CALIFA datacube (see Sections 3.2.1 and 4.1.1). Table 4 also indicates the class and type of asymmetries detected in the [O iii] emission line profiles in each object (see Sections 3.3 and 4.2). Each column in Table 4 corresponds to:
Column : Object
Columns -: Sytemic velocities derived from:  [O ii] (V);  [O iii] (V);  H+[N ii] (V); and  [SII] (V) emission lines.