The coordinated growth of stars, haloes and large-scale

structure since z=1

Michael BaloghDepartment 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 ~3x1010 MSun

• 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?

www.nbody.net

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, ~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

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. 2005

[-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/0607648 )

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 )

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 predictionsCroton 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~1DEEP2, (also CFHTLS, VVDS)

EDiSCs• At 0<z<1, passive fraction

correlates well with the fraction of galaxies in groups at z>2.

• At z~0, the cluster environment further suppresses star formation.

Poggianti et al. (2006)

Environments at z~1

• d

DEEP2 (Cooper et al. 2006)

Environments at z~1DEEP2 (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

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.