The coordinated growth of stars, haloes and large-scale structure since z=1 Michael Balogh Department of Physics and Astronomy University of Waterloo

Outline What determines a galaxy’s properties?  Stellar mass  Cosmic time  Environment Theoretical expectations:  Dark matter: halo mass function and growth history  Gas accretion and feedback  “Local” processes (e.g. merging, stripping etc.)

Colour distribution Millennium GC: Driver et al. (2006) Bimodality in colour distribution used to simplify analysis Very useful, but hides many details

Stellar mass Characteristic stellar mass ~3x10 10 M Sun Star formation today occurs in low-mass galaxies Kauffmann et al. (2003)

Cosmic Time buildup of mass on the red-sequence occurs with the most massive galaxies first decrease in the “quenching” stellar mass with redshift Cimatti et al. (2006)

Environment Nearby cluster galaxies differ in their:  SFR  Colour  Stellar mass function  HI gas  Morphology Lots of evidence that trends are independent of stellar mass. Also morphology (Christlein & Zabludoff 2005) All trends observed in clusters appear to extend to groups, field environments Lewis et al. (2001)

The halo model Formation history is tightly coupled to dark matter halo mass: small haloes form first Dark matter mass function depends on environment Mass accretion rate depends on environment (Maulbetsch et al. 2006).  Could give rise to observed trends?

The halo model Formation history is tightly coupled to dark matter halo mass: small haloes form first Dark matter mass function depends on environment Mass accretion rate depends on environment (Maulbetsch et al. 2006).  Could give rise to observed trends? Maulbetsch et al. (2006) Halo mass Cosmic Time

The halo model Formation history is tightly coupled to dark matter halo mass: small haloes form first Dark matter mass function depends on environment Mass accretion rate depends on environment (Maulbetsch et al. 2006).  Could give rise to observed trends? Maulbetsch et al. (2006) Halo mass Cosmic Time

Gas Accretion Halo mass scale constant with time, ~2x10 11 M Sun. Separates “hot” and “cold” accretion (e.g. White & Frenk 1991) AGN feedback helps eliminate bright blue galaxies (Springel et al. 2005; Croton et al. 2006; Bower et al. 2006) Dekel & Birnboim 2006

Environment: predictions? Galaxy colour depends primarily on halo mass. Satellites are effectively quenched. Low stellar-mass, red galaxies are predicted to be in groups, above the critical mass limit Ignore (details of) ram pressure stripping, harassment etc.  Know these occur in rich clusters

My summary from Ringberg 2005: When feedback parameters are tuned to reproduce the field luminosity function and colour distribution, what will we find as a function of environment?  General trends will be reproduced. But will it be for the right reasons?  Any differences in detail: will they signify “nurture” processes? Or just that feedback parameters need further tuning?

Halo mass dependence Method 1: can try to select groups and clusters from the observations in a way that is similar to N- body halo-finders. Late-type fraction depends most strongly on halo mass R luminosity Weinmann et al [-21,-22] [-22,-23] [-20,-21] [-19,-20] [-18,-19]

Halo mass dependence Faint, satellite galaxies are blue Models too efficient at shutting off gas supply? Weinmann et al. 2006

Local environment Method 2: Use an observationally- motivated, continuous measurement of environment Red fraction is a continuous function of local density and stellar mass Baldry et al. (astro-ph/ )

Universal relation Red fraction appears to depend on a simple linear combination of stellar mass and density Reflects the fact that stellar mass and density are correlated Baldry et al. (astro-ph/ )

Theoretical predictions Croton et al. (2006) models, based on the Millennium simulation

Theoretical predictions Croton et al. (2006) models, based on the Millennium simulation Data

Theoretical predictions Bower et al. (2006) models, based on the Millennium simulation

Theoretical predictions Bower et al. (2006) models, based on the Millennium simulation

Theoretical predictions Croton et al. (2005) Bower et al. (2006)

Theoretical predictions Both models get general trends right Both models predict too many red galaxies in the densest region Central galaxies in Croton model are too frequently blue Croton et al. (2005) Bower et al. (2006)

Isolated galaxies The 50 most isolated, nearby galaxies “Certain” to be central: useful comparison to models. Continuous sequence?

Increasing stellar mass

Environment: Redshift evolution Strong evolution out to z~0.5  EDiSCs (also MORPHS, CNOC, PISCES, many others)  Production of S0 galaxies? Environmental effects visible at z~1  DEEP2, (also CFHTLS, VVDS)

EDiSCs At 0 2. At z~0, the cluster environment further suppresses star formation. Poggianti et al. (2006)

Poggianti the fraction of passive galaxies observed in z = 0.4–0.8 clusters of a given /mass is comparable with the fraction of its galaxies (or its mass) that was already in dense environments (i.e., groups) at z = 2.5. the observed fraction of passive galaxies in systems with > 500 km s-1 at z = 0 is compatible with the fraction of galaxies that have resided in a cluster (Msys > M ) for at least 3 Gyr and therefore have had the time to have their star formation switched off According to this discussion, while the passive galaxy populations of the distant clusters are predominantly composed of primordial passive galaxies, the populations of lower redshift clusters are dominated by quenched galaxies.

Environments at z~1 d DEEP2 (Cooper et al. 2006)

Environments at z~1 DEEP2 (Cooper et al. 2006) 0.75<z<1.35 SDSS

Environments at z~1 DEEP2 (Cooper et al. 2006) SDSS (Blanton et al. 2005) At z~1, the luminosity of blue galaxies correlates with environment. i.e. brighter blue galaxies are in denser environment. These galaxies presumably evolve into the bright, red galaxies in dense environments today

Environments at z~1 At least 3% red galaxies in low density environments at all z Fewer galaxies above “critical mass” at higher redshift? i.e. is this just evolving mass function? DEEP2 (Cooper et al. 2006)

Summary Environment – in one way or another – is as important as stellar (halo?) mass Hypothesis that cooling is shut off in haloes above a critical mass seems to work.  Efficiency and timescale (and therefore physical mechanism) still uncertain  Need to move beyond bimodality to find out how the transformation is occurring.