Galaxies in Clusters to z~1Erica 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 relationsButcher-Oemler effect (clusters at higher-z have more star formation)

Unique environmental mechanismsRelation to hierarchical structure formation

Challenge: finding homogeneous samples of clusters to high redshift

RCS SurveysRCS-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 isolatered galaxies at 0.2 < z < 1.0

Large sample of uniformly selected clusters at high redshift

,

Z=0.87

Sample detailsThis analysis:~1000 clusters 0.4 < z < 0.9Original R and z’ survey data

Photometric cluster redshifts to about 10% (Blindert et al., 2007, Gilbank et al. 2007)

Richnesses = excess < 0.5Mpc in red sequenceBgcred > 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 > 800

Bgc > 500

Bgc > 300

Composite C-M Diagrams

Stacked regions scaled by r200 around each cluster

Statistical background correction

minus

Equals ->

R-z’

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 0.5R200M*

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 populationsObserved 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 galaxiesRed 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)

CWW colors

Cluster infall: an empirical modelClusters 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 infallInfalling 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

Z=0.87

See also Kodama & Bower 2001, Ellingson et al 2001

Luminosity functions

Green line: Schechter function fit at z=0.4 + passive evolution Gilbank et al. 2008

z=0.4 top left

z=0.9 bottom right

Bgc >500

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

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

Rich, low-zclusters fromBarkhouse et al.2007, Hansen, et al.2007

LF- blue galaxies

There appear to be sufficient blue galaxies of similar or larger luminosity to create the faint red sequence.

Infalling groupsSample: 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 EnvironmentInside 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

SummaryStatistical samples of galaxy clusters from the RCS survey produce bimodal galaxy distributions:Red sequence galaxies…Have colors similar to R/S field galaxiesAppear to evolve passivelyAre an increasing fraction of the cluster populationHave increasing numbers of faint galaxies

Blue galaxies…Have colors similar to blue cloud field galaxiesAre spatially more extended, suggesting recent infalling populationDecrease 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 observationsRCS-2: 1000 square degrees, observations 90% complete….

Broad ConclusionsBroad 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 transformationsRole of starbursts and AGN