Galaxies in Clusters to z1

1
Galaxies in Clusters to z1

• 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)

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The Evolution of Galaxies in Clusters

• Key issues
• Formation of the z0 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

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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 R24.8, z23.6
• 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 lt z lt 1.0
• Large sample of uniformly selected clusters at
  high redshift
• ,

Z0.87
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Sample details

• This analysis
• 1000 clusters
• 0.4 lt z lt 0.9
• Original R and z survey data
• Photometric cluster redshifts to about 10
• (Blindert et al., 2007, Gilbank et al. 2007)
• Richnesses excess lt 0.5Mpc
• in red sequence
• Bgcred gt 300 Mpc1.77
• gt 300 km s-1
• R200 estimated from
• Bgc-Mass calibrations
• (e.g., Yee Ellingson 1993,
• Blindert et al., 2007, Hicks et al. 2008)

Bgc gt 300
Bgc gt 500
Bgc gt 800
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Composite C-M Diagrams

• Stacked regions scaled by r200 around each
  cluster
• Statistical background correction

minus
R-z
Equals -gt
z mag
6

• Rectified C-M relation relative to m(z) on red
  sequence and R-z color of m
• (effectively passively evolving)
• m lt m1.5
• Additional k-correction for
• non-red sequence galaxies as a function of
  observed color
• Final distribution is close to stellar-mass
  limited

Z0.87 within 0.5R200
M
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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

z0.87
z0.7
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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
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Cluster selection and contamination

• Clusters are selected by presence of red sequence
  brighter than m0.5. Should not necessarily
  bias properties of blue galaxies
• Complete to Bgc500, blue fraction lt 0.8 at zlt 1
  (Gladders, 2002)
• Possibly missed some poor, blue clusters z gt 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.

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Colors of blue galaxies (m lt m1.5)
Colors of galaxies span expectations for normal
field populations Observed B/O effect is not
driven by excess of blue starbursting galaxies
z0 colors 100Myr SSB Irr Sbc Sab widths
are projection of z bin
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Colors of cluster galaxies
CWW colors

• Red lineCluster 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)

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Cluster infall an empirical model

• Clusters built from infall of near-field (R/R200
  gt 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 z0 clusters
  (Biviano et al. 2002) more experienced cluster
  galaxies follow NFW

Z0.5
See also Kodama Bower 2001, Ellingson et al
2001
Z0.87
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Luminosity functions
z0.4 top left z0.9 bottom right Bgc gt500

• Green line Schechter function fit at z0.4
  passive evolution
• Gilbank et al. 2008

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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

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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

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LF- blue galaxies
There appear to be sufficient blue galaxies of
similar or larger luminosity to create the faint
red sequence.
17
Infalling groups

• Sample CNOC, 15 massive clusters, 0.18 lt z lt
  0.55
• 4-color photo-z 1000 spectroscopic zs 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 z0.23
rCL r/r200
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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

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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

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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.
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Broad Conclusions

• Broad scenario of a cosmologically-driven decline
  in the infall of star-forming galaxies into
  clusters since z1
• 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