luminosity & color of
galaxies in clusters
sarah m. hansen
university of chicago
with
erin s. sheldon (nyu)
risa h. wechsler (stanford)
astrophysics with eV photons
sarah m. hansen
university of chicago
with
erin s. sheldon (nyu)
risa h. wechsler (stanford)
outline

motivation

sdss data & cluster sample
characterizing the galaxy population



luminosity function: dependence on cluster mass,
galaxy color
blue fraction: dependence on cluster mass, redshift,
galaxy luminosity & cluster-centric radius
sarah m. hansen
glcw8
motivation

clusters as cosmological probes



clusters as galaxy evolution laboratories


how to connect dark and luminous matter?
how to connect stars and gas?
what’s happened to form such a particular cluster
galaxy population?
for upcoming large surveys, want to
understand these details better
sarah m. hansen
glcw8
sdss clusters

> 7300 deg2 of ugriz
photometric data

maxBCG clusters




red sequence matched filter
(koester et al. 2007a,b)
z ≤ 0.3; Dz ~ 0.01
mass proxy: N200
mass - richness scaling




mass function & cosmological
params (rozo et al. 2007)
velocity dispersion
(becker et al. 2007)
lensing (sheldon et al.;
johnston et al.)
x-ray (rykoff et al.)
sarah m. hansen
13,823 systems
with N200 ≥ 10
and z ≤ 0.3
glcw8
method

measure background-subtracted, k-corrected
distribution of galaxies associated with clusters,
binned by cluster & galaxy properties
galaxy properties cluster properties
BCG or not?
richness
radial distance
total luminosity
luminosity
redshift
color
BCG properties
• luminosity function as f (richness, color)
• blue fraction as f (richness, redshift, radius, luminosity)

comparison with ADDGALs simulations (wechsler et al.)
sarah m. hansen
glcw8
conditional luminosity function
(L|M):
important
ingredient for
understanding
how galaxies
populate halos
sarah m. hansen
glcw8
color distribution
red galaxies; blue galaxies
all galaxies
radial color trend is due to changing number of
galaxies on the red sequence vs in the blue cloud
 blue fraction is the info you need
sarah m. hansen
glcw8
blue fraction within r200
provides constraints
on models of galaxy
populations and
evolution in clusters
sarah m. hansen
glcw8
blue fraction within r200
provides constraints
on models of galaxy
populations and
evolution in clusters
sarah m. hansen
glcw8
blue fraction, in more detail
radial trend
sarah m. hansen
luminosity trend
glcw8
summary
with sdss data and galaxy-populated simulations, we
investigate the properties of cluster galaxies, including:


conditional luminosity function
for all, red & blue galaxies
blue fraction as a function of cluster
mass, redshift, radius and magnitude
see hansen et al., arXiv:0706.soon
sarah m. hansen
glcw8