Post on 13-Jan-2016
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.