The coordinated growth of stars, haloes and large-scale structure since z=1

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

2. 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.)

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

4. Stellar mass • Characteristic stellar mass ~3x1010 MSun • Star formation today occurs in low-mass galaxies Kauffmann et al. (2003)

5. 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)

6. Environment • Nearby cluster galaxies differ in their: • SFR • Colour • Stellar mass function • HI gas • Morphology Lewis et al. (2001) • 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

7. 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? www.nbody.net

8. The halo model Maulbetsch et al. (2006) • 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? Halo mass Cosmic Time

9. The halo model Maulbetsch et al. (2006) • 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? Halo mass Cosmic Time

10. Gas Accretion • Halo mass scale constant with time, ~2x1011 MSun. • 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

11. 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

12. 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?

13. [-22,-23] [-21,-22] [-20,-21] [-19,-20] [-18,-19] Halo mass dependence R luminosity • 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 Weinmann et al. 2005

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

15. 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/0607648)

16. 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/0607648)

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

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

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

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

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

22. 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)

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

24. Increasing stellar mass

25. 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)

26. EDiSCs • At z~0, the cluster environment further suppresses star formation. • At 0<z<1, passive fraction correlates well with the fraction of galaxies in groups at z>2. Poggianti et al. (2006)

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

28. Environments at z~1 SDSS (Blanton et al. 2005) DEEP2 (Cooper et al. 2006) • 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

29. 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.