Galaxy Populations In Groups Research Articles

Galaxy Populations in Groups and Clusters: Evidence for a Characteristic Stellar Mass Scale at M ∗ ∼ 109.5 M ⊙

We use the DR9 of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass M h ≥ 1012 M ⊙ and redshift 0.01 ≤ z ≤ 0.08, down to a limiting r-band magnitude of M r = −10 to −12. For given halo masses we measure the CLF for the total populations and for the red and blue populations classified using the (g − z) color. We find a clear faint-end upturn in the CLF of red satellites, with a slope α ≈ −1.8, which is almost independent of halo mass. This faint-end upturn is not seen for the blue and total populations. Our stellar population synthesis modeling shows that (g − z) provides a clean red/blue division and that red group galaxies defined by (g − z) are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at M r ∼ −18, corresponding to M * ∼ 109.5 M ⊙. This scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)−sized halos is in good agreement with the quenched fraction measured for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies and for the stellar mass functions of low-mass galaxies to be observed at high redshift.

Effects of superstructure environment on galaxy groups

We analyse properties of galaxy groups and their dependence on the large scale environment as defined by superstructures. We find that group galaxy cross correlations depend only on group properties regardless the groups reside in superstructures. This indicates that the total galaxy density profile around groups is independent of the global environment. At a given global luminosity, a proxy to group total mass, groups have a larger stellar mass content by a factor 1.3, a relative excess independent of the group luminosity. Groups in superstructures have 40 per cent higher velocity dispersions and systematically larger minimal enclosing radii. We also find that the stellar population of galaxies in groups in superstructures is systematically older as infered from the galaxy spectra Dn4000 parameter. Although the galaxy number density profile of groups is independent of environment, the star formation rate and stellar mass profile of the groups residing in superstructures differs from groups elsewhere. For groups residing in superstructures, the combination of a larger stellar mass content and star formation rate produces a larger time scale for star formation regardless the distance to the group center. Our results provide evidence that groups in superstructures formed earlier than elsewhere, as expected in the assembly bias scenario.

THE GALAXY CONTENT OF SDSS CLUSTERS AND GROUPS

Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of brightest cluster galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {<=} z {<=} 0.3. The size of the data set allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r {sub 200} of clusters with mass above 3 x 10{sup 13} h {sup -1} M {sub sun}, the luminosity function (LF) of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite LF does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25} M{sub i} - 5log{sub 10} h =-19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity, and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L {sub BCG} {approx} Mmore » {sup 0.3} {sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub logL} {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.« less

MIDLIFE CRISES IN DWARF GALAXIES IN THE NGC 5353/4 GROUP

This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 × 1013 M ☉) NGC 5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass-to-light ratio M/LR = 105 M ☉/L ☉ is a factor of 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early-type galaxies. By comparison, the NGC 5353/4 Group lacks superluminous systems but has a large fraction of intermediate-luminosity galaxies; or equivalently, a luminosity function with a flatter faint-end slope. The luminosity function for the NGC 5353/4 Group should steepen as the intermediate-luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star-formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.

The evolution of the bimodal colour distribution of galaxies in Sloan Digital Sky Survey groups

We analyse u - r colour distributions for several samples of galaxies in groups drawn from the fourth data release of the Sloan Digital Sky Survey. For all luminosity ranges and environments considered, the colour distributions are well described by the sum of two Gaussian functions. We find that the fraction of galaxies in the red sequence is an increasing function of group virial mass. We also study the evolution of the galaxy colour distributions at low redshift, z ≤ 0.18 in the field and in groups for galaxies brighter than M r - 5 log (h) = -20, finding significant evidence of recent evolution in the population of galaxies in groups. The fraction of red galaxies monotonically increases with decreasing redshift, this effect implies a much stronger evolution of galaxies in groups than in the field.