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Galaxies in Clusters to z~1
Erica Ellingson, U. Colorado
RCS Team: H Yee (U. Toronto), M. Gladders (U. Chicago)
D. Gilbank (U. Waterloo), Y.S. Loh (UCLA),
I-Hui Tornado Li (Swinburne)
H. Hoekstra (Leiden),), T. Webb (McGill)
Rebin Yan (Toronto), K. Blindert (MPIA Heidelberg)
A. Hicks (Michigan State), M. Bautz (MIT),
F. Barrientos (U. Catholica, Chile)
The Evolution of Galaxies in Clusters
Key issues:
Formation of the z=0 red sequence
(cluster-field differential)
Morphology-density/radius relations
Butcher-Oemler effect
(clusters at higher-z have more star formation)
Unique environmental mechanisms
Relation to hierarchical structure formation
Challenge: finding homogeneous samples of
clusters to high redshift
RCS Surveys
RCS-1 is a 90 square degrees
wide field 2-filter imaging
survey at CFHT and CTIO
(Gladders & Yee 2005,
Gladders et al. 2006)
Complete to R=24.8, z’=23.6
Searches for overdensities
in the color-magnitude diagram
along the red sequence of
cluster galaxies. Filters are
chosen to isolate
red galaxies at 0.2 < z < 1.0
Large sample of uniformly
selected clusters at high
redshift
Z=0.87
Sample details
This analysis:
~1000 clusters
0.4 < z < 0.9
Original R and z’ survey data
Photometric cluster redshifts to
about 10%
Bgc > 300
(Blindert et al., 2007, Gilbank et al. 2007)
Richnesses = excess < 0.5Mpc
in red sequence
Bgcred > 300 Mpc1.77
 >~ 300 km s-1
R200 estimated from
Bgc-Mass calibrations
(e.g., Yee & Ellingson 1993,
Blindert et al., 2007, Hicks et al. 2008)
Bgc > 500
Bgc > 800
Composite C-M Diagrams
Stacked regions scaled by r200
around each cluster
Statistical background correction
minus
R-z’
Equals ->
z’ mag
Rectified C-M relation relative to
m*(z) on red sequence and
R-z’ color of m*
(effectively passively evolving)
m < m*+1.5
Additional k-correction for
non-red sequence galaxies as a
function of observed color
Final distribution is close to
stellar-mass limited
Z=0.87 within 0.5R200
M*
Bimodality in galaxy colors
• Bimodality is seen at all redshifts (see also Gerke et al. 2007)
• Red sequence fit as double-gaussian on the red side and
mirrored
• Profile is due to both observational error in colors and
cluster redshift uncertainties
z=0.7
z=0.87
Butcher-Oemler effect ~ Red fraction (z)
Butcher-Oemler effect:
more blue galaxies
(fewer red ones) at
higher redshift
(e.g., Butcher & Oemler 1978,
many others since!)
Clusters are bluer at
larger radii- infalling
galaxies?
(e.g. Biviano et al. 2002)
Change is faster at larger
radii- changing infall
rates
(e.g., Ellingson et al. 2001,
Poggianti et al. 2006)
Loh, et al. 2008
Cluster selection and contamination
Clusters are selected by presence of red sequence brighter than
~m*+0.5. Should not necessarily bias properties of blue galaxies
Complete to Bgc=500, blue fraction < 0.8 at z< 1 (Gladders, 2002)
Possibly missed some poor, blue clusters z > 0.8
Probable contamination ~10% from spectroscopy and X-ray
observations of RCS clusters (Blindert et al. 2007, Gilbank et al.,
2007, Hicks et al. 2007), simulations (Cohen et al. 2007)
Primary challenge-- uncertainties in mass estimates/R200. These plus
centroiding errors will flatten radial distributions.
Colors of blue galaxies (m < m*+1.5)
Colors of galaxies span expectations for normal field
populations
Observed B/O effect is not driven by excess of blue
starbursting galaxies
z=0 colors: 100Myr SSB Irr Sbc Sab
widths are projection of z bin
Colors of cluster galaxies
CWW colors
Red line=Cluster red sequence
Blue squares = median color of
the cluster blue cloud
Solid dots- median field galaxy
colors for matched redshift
and magnitude cuts
(courtesy of Eric Bell)
Blue galaxies in clusters are
generally consistent with an
infalling coeval field
population
Hidden: star formation rates,
obscured starbursts, dust….
(e.g. Saintonge 2008, many
others)
Cluster infall: an empirical model
Clusters built from infall of near-field (R/R200 > 2.5) populations (already
quite red at lower z)
Cosmological infall rates (e.g., Berrier et al 08)
Blue galaxies turn red 1.5 Gyr after infall
Infalling galaxies have same extended spatial profile as infalling galaxies in
z=0 clusters (Biviano et al. 2002); more experienced cluster galaxies
follow NFW
Z=0.5
See also
Kodama & Bower 2001,
Ellingson et al 2001
Z=0.87
Luminosity functions
z=0.4 top
left
z=0.9
bottom
right
Bgc >500
Green line: Schechter function fit at z=0.4 + passive evolution
Gilbank et al. 2008
LF-red sequence galaxies
Green model is the same- note gradual increase in fraction of
red sequence galaxies
Vertical lines are MV = -23, -21, -20 define “luminous” and “faint”
Bright/faint ratios on the red sequence
Rich, low-z
clusters from
Barkhouse et al.
2007,
Hansen, et al.
2007
Similar qualitatively and quantitatively to DeLucia et al. 2006
(see also Tanaka et al. 2005, Stott, et al. 2007, Gilbank &Balogh 2008)
Build-up of faint red sequence is consistent with downsizing
scenarios
LF- blue galaxies
There appear to be sufficient blue galaxies of similar or larger
luminosity to create the faint red sequence.
Infalling groups
Sample: CNOC, 15 massive
clusters, 0.18 < z < 0.55
4-color photo-z + ~1000
spectroscopic z’s from CFHT
Cluster galaxy maps to 1.5-3 r200
FoF group-finding algorithm,
Local density measurements
Red fractions from cuts in C-M
diagram (numbers are not
quite the same as earlier plots)
Li, et al. 2008
A2390 at z=0.23
rCL= r/r200
Local vs. Global Environment
Inside the virial radius (rcl ~ 1), flat gradients of of red
fraction with local galaxy density indicate that
cluster radius determines population
Infalling Groups
• Infalling groups are not greatly affected by cluster infall
• Preprocessing, esp. at lower z
• Group colors are evolving more quickly than cluster
cores- downsizing again
Summary
Statistical samples of galaxy clusters from the RCS survey
produce bimodal galaxy distributions:
Red sequence galaxies…
Have colors similar to R/S field galaxies
Appear to evolve passively
Are an increasing fraction of the cluster population
Have increasing numbers of faint galaxies
Blue galaxies…
Have colors similar to blue cloud field galaxies
Are spatially more extended, suggesting recent infalling population
Decrease as the red galaxies increase
Still to come from RCS-1: targeted studies of ~40 cluster “core sample” for
IMACS optical spectroscopy, HSTsnapshots, weak lensing, and Spitzer IRAC
and MIPS observations
RCS-2: 1000 square degrees, observations 90% complete….
Broad Conclusions
Broad scenario of a cosmologically-driven decline in the infall of star-forming
galaxies into clusters since z~1
infalling galaxies quench their star formation quickly (or even before entereing
the cluster), evolve to the (moderately) faint red sequence
Sequence shows downsizing on both galaxy and cluster scales
Mechanisms still be be explained:
Quenching mechanisms: why and where??
Morphological and dynamical transformations
Role of starbursts and AGN