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Galaxies in Clusters to z~1

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)

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Galaxies in Clusters to z~1

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  1. 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)

  2. 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

  3. 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

  4. Sample details • This analysis: • ~1000 clusters • 0.4 < z < 0.9 • Original 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 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 > 300 Bgc > 500 Bgc > 800

  5. Composite C-M Diagrams Stacked regions scaled by r200 around each cluster Statistical background correction minus R-z’ Equals -> z’ mag

  6. 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*

  7. 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=0.87 z=0.7

  8. 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

  9. 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.

  10. 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 SSBIrr Sbc Sab widths are projection of z bin

  11. 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)

  12. 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

  13. 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

  14. 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”

  15. 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-z clusters from Barkhouse et al. 2007, Hansen, et al. 2007

  16. 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 < 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

  18. 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

  19. 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

  20. 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….

  21. 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

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