ASTR 616 Chas Miller
Summary of:
On the Luminosity Function of Galaxies in Groups in the
Sloan Digital Sky Survey
Authors: Ariel Zandivarez, Hector J. Martinez, and Manuel E. Merchan,
Universidad Nacional de Cordoba
arXiv:astro-ph/0602405 17 February, 2006
Overview
Using SDSS Data from Release 4, the authors identify 14004 galaxy groups containing
85,728 galaxies and match Schechter functions to groups as a whole in each Sloan band,
and then match Schechter functions according to group mass, according to red vs. blue
galaxy populations, and between groups with a “dominantly bright” galaxy and those
without a single dominantly bright galaxy. They find statistically significant correlations
of Schechter parameters alpha and M* to each of these variables.
Summary
As described above the authors fit Schechter functions to various populations of
galaxies within groups, varying alpha and M* as the free parameters. They report the
following results:
The authors match alpha and M* parameters for six bins of approximately 2200
groups each according to group mass. They find that as group mass increases, alpha
increases while M* gets progressively brighter. For the lowest mass groups (1e11 to
8e12 solar masses), M* = -20.44 +/- 0.04 and alpha = -0.93 +/- 0.03. For the highest
mass groups (> 1.8e14 solar masses), M* = -21.20 +/- 0.04 and alpha = -1.29 +/- 0.03.
The authors then split the galaxy populations in each group mass bin into red and blue
populations and map alpha and M* against group mass separately for the red and blue
populations. They utilize a bimodal (u-r) distribution plotted against r absolute
magnitude to separate the red and blue populations. They discover a stronger change
in M* and alpha as a function of group mass for the red galaxies (delta M* of 1.05
delta alpha of 0.75) as compared to the blue galaxies (delta M* of 0.5 delta alpha of
0.30). They propose that these trends in the red population support the idea of
extensive mergers in the history of the red galaxies in as merger frequency is expected
to be a function of group mass (less massive groups have less mergers due to a smaller
velocity dispersion). The difference in merger rates as a function of group mass results
in a difference in Schechter parameters over time. In contrast, the more narrow range
of Schechter parameters in the blue populations suggests evolution of blue galaxies is
largely independent of local environment.
The authors also divided the galaxy groups into two bins according to the dominance
of the brightest galaxy in a group. They compared the brightness of the brightest
