We use a friends-of-friends algorithm to identify loose groups from the northern CfA2 survey covering the region 8h<={alpha}_(1950)_<=17h and 8.5{deg}<={delta}_(1950)_<=44.5{deg}. There are 406 groups; 149 of these contains five or more members within the survey. Geometric simulations guide our choice of the selection parameters; {delta}{rho}/{rho}=80 is the limiting density contrast and V0=350km/s is the fiducial velocity linking parameter. The geometric simulations are particularly important for evaluating the impact of large-scale structure (e.g., the Great Wall) on group selection. The physical parameters of this large sample are coincident with our earlier results [126 groups in Ramella et al. (1989ApJ...344...57R)]: the median velocity dispersion in 192 (156; 229)km/s and the median blue log(M/L) is 2.38 (2.20; 2.52). The mass-to-light ratio (M/L) is in units of Msun/Lsun for an assumed Hubble constant, H0=100km/s/Mpc. The numbers in parentheses are 99% confidence limits. This group catalog provides a substantially larger sample for statistical studies than has been previously available. For example, it provides a more substantial sample for estimation of the distribution of group velocity dispersions and of the group-group correlation function. (Copyright) 1997 American Astronomical Society.
The catalog contains statistically homogeneous and physically well graunded groups of galaxies based on the CfA2 redshift survey (Cat. J/ApJS/121/287) in the area of space 1000km/s<=cz<=15000km/s, |bII|>=20{deg}. For identification of groups we used a modification of a friends of friends (FoF) method. Principles of friendship and definition of values of presented there free parameters described in Mahtessian (1988Afz....28..255M, 1997Ap.....40..285M). There are 1971 groups with 2 or more members, for a total of 6787 members (46.3%); 765 of the groups have 3 or more members with 4375 galaxies (28.1%). The others 8790 (56.4%) galaxies make a sample of "single" galaxies. The catalog includes group numbers, numbers of members, equatorial coordinates, Virgo-centric radial velocities, line-of-sight-velocity dispersions, integrated group luminosities, and relative quantity of false members.
The catalog contains statistically homogeneous groups of galaxies based on the Harvard-Smithsonian Center for Astrophysics (CfA) redshift survey. Groups in the catalog are all density enhancements in redshift space of a factor greater than 20. All groups contain at least three members. There are 176 groups in the catalog and 102 groups have been identified in one or more previous studies. The catalog includes group numbers, numbers of members, equatorial coordinates, mean flow-corrected galactocentric velocities, line-of-sight-velocity dispersion, integrated group magnitudes, crossing times for the groups, and mean harmonic radii of the groups.
The catalog contains nearby groups of galaxies with outer number density enhancement greater than 20. The groups were searched using a whole sky catalog of 1312 galaxies brighter than mag 13.2 (B) with complete redshift information (Huchra et al. =1983ApJS...52...89H). Only groups containing more than two members are included. The catalogue includes equatorial coordinates, average radial velocities, and velocity dispersions for 92 nearby groups in the first file. A second file contains the results of a comparison between this catalog and de Vaucouleurs' (1975) catalog of nearby groups The Hubble constant was assumed 100km/s/Mpc.
We present a large catalog of galaxy loose groups in the Southern Galactic Hemisphere, selected from the Perseus-Pisces redshift Survey (PPS). Particular care is taken in order to obtain group samples as homogeneous as possible to previously published catalogs. Groups are identified with the adaptive Friends-of-Friends (FoF) algorithm of Huchra & Geller (1982ApJ...257..423H), with suitable normalizations V_0_=350km/s and D_0_=0.231h.Mpc. As a necessary ingredient of FoF algorithms, we obtain the galaxy luminosity function (LF) for PPS. Its Schechter parameters ({alpha}=-1.15+/-0.15, M_*_=-19.3+/-0.1) are in good agreement with similar LF estimates from samples previously used to select groups. The LF normalizations {phi}_*_=0.02h^3^/Mpc^3^ appropriate for PPS yields a density threshold {delta}n/n~180 for the adopted D_0_, apparently rather different from the desired {delta}n/n~80 used in previous studies. We then consider several other link normalizations, and briefly discuss their effect on group properties. We suggest to replace the customarily adopted {delta}n/n parametrization with the more direct D_0_ parametrization. All our catalogs contain N_G_~200 groups, significantly more than in most previous studies where group samples were obtained from galaxy data sets of comparable quality to (but smaller extent than) PPS. The group properties are rather sensitive to the adopted D_0_ and V_0_, but vary little with different redshift corrections, redshift cut-off, and galaxy LF. Loose groups in PPS nicely trace the large scale structure (LSS) in the parent galaxy sample. Physical properties of groups in PPS and in other directly comparable samples are in good agreement. There seems to be a complex interplay among LSS features, FoF grouping procedure, and group properties.
This paper aims to provide aperture corrections for emission lines in a sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey (CALIFA; Sanchez+, 2012A&A...538A...8S) database. In particular, we explore the behavior of the log([OIII]{lambda}5007/H{beta})/([NII]{lambda}6583/H{alpha}) (O3N2) and log[NII]{lambda}6583/H{alpha} (N2) flux ratios since they are closely connected to different empirical calibrations of the oxygen abundances in star-forming galaxies. We compute the median growth curves of H{alpha}, H{alpha}/H{beta}, O3N2, and N2 up to 2.5R_50_ and 1.5 disk Reff. These distances cover most of the optical spatial extent of the CALIFA galaxies. The growth curves simulate the effect of observing galaxies through apertures of varying radii. We split these growth curves by morphological types and stellar masses to check if there is any dependence on these properties. The median growth curve of the H{alpha} flux shows a monotonous increase with radius with no strong dependence on galaxy inclination, morphological type, and stellar mass. The median growth curve of the H{alpha}/H{beta} ratio monotonically decreases from the center toward larger radii, showing for small apertures a maximum value of ~10% larger than the integrated one. It does not show any dependence on inclination, morphological type, and stellar mass. The median growth curve of N2 shows a similar behavior, decreasing from the center toward larger radii. No strong dependence is seen on the inclination, morphological type, and stellar mass. Finally, the median growth curve of O3N2 increases monotonically with radius, and it does not show dependence on the inclination. However, at small radii it shows systematically higher values for galaxies of earlier morphological types and for high stellar mass galaxies. Applying our aperture corrections to a sample of galaxies from the SDSS survey at 0.02<=z<=0.3 shows that the average difference between fiber-based and aperture-corrected oxygen abundances, for different galaxy stellar mass and redshift ranges, reaches typically to ~11%, depending on the abundance calibration used. This average difference is found to be systematically biased, though still within the typical uncertainties of oxygen abundances derived from empirical calibrations. Caution must be exercised when using observations of galaxies for small radii (e.g., below 0.5 Reff) given the high dispersion shown around the median growth curves. Thus, the application of these median aperture corrections to derive abundances for individual galaxies is not recommended when their fluxes come from radii much smaller than either R_50_ or Reff.
We present a detailed study of the stellar and HI structure of the dwarf irregular galaxies Sextans A and Sextans B, members of the NGC3109 association. We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the Surface Brightness (SB) profiles of the two galaxies down to mu_V_~31.0mag/arcsec^2^. We find that both galaxies are significantly more extended than what previously traced with surface photometry, out to ~4kpc from their centers along their major axis. Older stars are found to have more extended distribution with respect to younger populations. We obtain the first estimate of the mean metallicity for the old stars in Sex B, from the color distribution of the Red Giant Branch, <[Fe/H]>=-1.6. The SB profiles show significant changes of slope and cannot be fitted with a single Sersic model. Both galaxies have HI discs as massive as their respective stellar components. In both cases the HI discs display solid-body rotation with maximum amplitude of ~50km/s (albeit with significant uncertainty due to the poorly constrained inclination), implying a dynamical mass ~10^9^~M_{sun}_, a mass-to-light ratio M/L_V_~25 and a dark to-barionic mass ratio of ~10. The distribution of the stellar components is more extended than the gaseous disc in both galaxies. We find that the main, approximately round-shaped, stellar body of Sex A is surrounded by an elongated low-SB stellar halo that can be interpreted as a tidal tail, similar to that found in another member of the same association (Antlia). We discuss these, as well as other evidences of tidal disturbance, in the framework of a past passage of the NGC3109 association close to the Milky Way, that has been hypothesized by several authors and is also supported by the recently discovered filamentary configuration of the association itself
In this paper we introduce the deepest and most extensive ultraviolet extragalactic source catalogs of the Virgo Cluster area to date. Archival and targeted GALEX imaging is compiled and combined to provide the deepest possible coverage over ~120deg^2^ in the NUV (lambda_eff_=2316{AA}) and ~40deg^2^ in the FUV (lambda_eff_=1539{AA}) between 180{deg}<=RA<=195{deg} and 0{deg}<=DE<=20{deg}. We measure the integrated photometry of 1770 extended UV sources of all galaxy types and use GALEX pipeline photometry for 1,230,855 point-like sources in the foreground, within, and behind the cluster. Extended source magnitudes are reliable to m_UV_~22, showing a ~0.01{sigma} difference from their asymptotic magnitudes. Point-like source magnitudes have a 1{sigma} standard deviation within ~0.2mag down to m_uv_~23. The point-like source catalog is cross-matched with large optical databases and surveys including the SDSS DR9 (>1 million Virgo Cluster sources), the Next Generation Virgo Cluster Survey (NGVS; >13 million Virgo Cluster sources), and the NED (~30,000 sources in the Virgo Cluster). We find that 69% of the entire UV point-like source catalog has a unique optical counterpart, 11% of which are stars and 0.01% (129) are Virgo cluster members that are neither in the VCC nor part of the bright CGCG galaxy catalog (i.e., m_pg_<14.5). These data are collected in three catalogs containing the UV extended sources, the UV point-like sources, and the most relevant optical parameters of UV-optically matched point-like sources for further studies from SDSS. The GUViCS catalogs provide a unique set of data for future work on UV and multiwavelength studies in the cluster and background environments.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), we report high angular-resolution observations of the redshift z=3.63 galaxy H-ATLAS J083051.0+013224 (G09v1.97), one of the most luminous strongly lensed galaxies discovered by the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). We present 0.2"-0.4" resolution images of the rest-frame 188 and 419um dust continuum and the CO(6-5), H_2_O(2_11_-2_02_), and Jup=2H_2_O^+^ line emission. We also report the detection of H_2_^18^O(2_11_-2_02_) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ~1.5" diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO(6-5), H_2_O(2_11_-2_02_), and Jup=2H_2_O^+^ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H_2_O, and H_2_O^+^ line emission at sub-kiloparsec scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7+/-0.1kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is {mu}~10-11, the magnification of the line emission varies from 5 to 22 across different velocity components. The line emission of CO(6-5), H_2_O(2_11_-2_02_), and H_2_O^+^ have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase, with a total molecular gas mass of ~10^11^M_{sun}_. Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities LIR reaching 4x10^12^L_{sun}_, and the total LIR of G09v1.97 is (1.4+/-0.7)x10^13^L_{sun}_. The approaching southern galaxy (dominating from V=-400 to -150km/s relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of a_s_=0.4kpc, while the receding galaxy (0 to 350km/s) resembles an a_s_=1.2kpc rotating disk. The two galaxies are separated by a projected distance of 1.3kpc, bridged by weak line emission (-150 to 0km/s) that is co-spatially located with the cold dust emission peak, suggesting a large amount of cold interstellar medium (ISM) in the interacting region. As one of the most luminous star-forming dusty high-redshift galaxies, G09v1.97 is an exceptional source for understanding the ISM in gas-rich starbursting major merging systems at high redshift.
In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u-r colors of early-type galaxies (ETGs) are flat out to R_90_, while the colors monotonously turn blue when r>0.5 R_50_ for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV-r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R_90_. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ~50% of the ETGs have EW(H{alpha})>6.0 {AA}. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cores" and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.
