The influence of environment on galaxy populations

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The influence of environment on galaxy populations
Michael Balogh
University of Waterloo, Canada
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Outline

• Low redshift
• Simple trends encompass most of what we know of
  as environmental influences
• Models what works and what doesnt
• Redshift evolution
• The future whats next?

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The influence of environment on galaxy populations

• Populations
• Current star formation rate
• Recent star formation
• Stellar mass (average SFR)
• Morphology (of stars, neutral gas, ionized gas)
• AGN
• Gas content

• Environment
• Mass of dark matter halo
• Position within halo
• Local density
• Large-scale density

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The influence of environment on galaxy populations

• Nature vs. nurture?
• Entangled in current models
• Gas accretion, merger, and feedback history scale
  with halo mass.
• No longer the right question?
• A better question what physics operates in
  haloes of a given mass, at a given epoch?
• Todays population is the result of different
  environments at different epochs cannot try to
  isolate one mechanism as responsible for the
  observed trends.

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The local Universe
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Colour-magnitude distribution

• Nearby galaxies seem to fall into two
  surprisingly well-defined, smoothly varying
  distributions.
• Colour, luminosity, concentration, star formation
  rate

Blanton et al. 2004
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Colour-magnitude distribution

• Colour distribution in 0.5 mag bins can be fit
  with two Gaussians
• Mean and dispersion of each distribution depends
  strongly on luminosity
• Dispersion includes variation in dust,
  metallicity, SF history, and photometric errors
• At bright magnitudes, significant fraction of
  blue population contaminates red c.f. talk
  by Wolf.

Baldry et al. 2003
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• Fraction of red galaxies depends strongly on
  density. This is the primary influence of
  environment on the colour distribution.

• Mean colours depend weakly on environment
  transitions between two populations must be rapid
  (or rare at the present day)

Balogh et al. 2004
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• Fraction of red galaxies depends strongly on
  density. This is the primary influence of
  environment on the colour distribution.

• Mean colours depend weakly on environment
  transitions between two populations must be rapid
  (or rare at the present day)
• Trend is not completely absent for fainter
  galaxies but never dominant

Balogh et al. 2004
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The star-forming population

• Carter et al. (2001)
• 3150 nearby galaxies
• Ha for SF galaxies does not depend on environment
• Triggering of SF occurs on small spatial scales

• Rines et al. 2005 Ha distribution in virial,
  infall and field regions nearly identical.

• Hard to explain with simple, slow-decay models
  (e.g. Balogh et al. 2000)

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Colour and environment
Contours Galaxy numbers

• Bright, red galaxies luminosity strongly
  correlated with environment
• Remainder average density increases with
  colour.
• Trend driven by galaxies between the two peaks
• consistent with statement that blue peak colour
  is independent of environment, while red fraction
  varies strongly.

Contours Local density
Blanton et al. 2004
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SFR-colour

• Recent SDSS analysis split by colour and SFR
• Environment halo mass
• Use luminosity as tracer of mass. Compare with
  theoretical mass function

Log (SFR/M) (yr-1)
0.1(g-r)
Weinmann et al. 2005
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Halo mass dependence
R luminosity

• Environment halo mass
• Use luminosity as tracer of mass. Compare with
  theoretical mass function
• At fixed mass the late-fraction depends weakly on
  luminosity
• Late-type fraction depends most strongly on halo
  mass

Weinmann et al. 2005
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Halo mass dependence
R luminosity

• Average properties of galaxies in either peak is
  independent of halo mass
• But depends on luminosity

Weinmann et al. 2005
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Local effects?

• Still a (weak) trend with radius in haloes of
  fixed mass
• Dependence on luminosity (surprisingly?) weak

1014ltMlt1015
1013ltMlt1014
Weinmann et al. 2005
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Conformity

• Properties of satellite galaxies appear to be
  connected with properties of central (actually
  brightest) galaxy

Weinmann et al. 2005
Similar to effect seen in 2PIGG groups? See
Vince Ekes talk. Definition of central?
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Implications

• Simple dependence of late-type fraction on
  environment characterizes much of observed trends
  (e.g. SFR-density, morphology-density,
  colour-density etc.).
• Interpretation?
• Two modes of formation. Within each peak is
  variance due to dust, metallicity (second-order
  effects).
• Transitions Where do S0, EA fit in?
• Burst vs. continuous SFR (Kauffmann et al. 2005)

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Signs of Nurture Virgo spirals

• Ram-pressure stripping in Virgo

Kenney et al. 2003 Vollmer et al. 2004

• Truncated Ha disks in clusters

Koopmann Kenney 2004 also Vogt et al. 2004
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Signs of Nurture morphology and SFR

• Passive Spirals
• EA galaxies?
• S0, dSph, UCDs
• Wolfs dusty spirals? Peak in infall region?

• e.g. Christlein Zabludoff (2005)
• Residual OII after subtracting expectation for
  given B/T, D4000 and Mstar.
• SFR gradient is not entirely
• Consequence of MDR
• Consequence of change in mass function
• Effect of initial conditions

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HI gas

• Springob et al. 2005 HIMF in dense regions
  flatter? May suggest smaller galaxies more HI
  deficient

HI deficiency in 18 nearby clusters Solanes et
al. 2001
High-density
Low-density
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AGN

• AGN fraction independent of density
• Surprising?

Miller et al. (2003)
Carter et al. (2001)
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Models
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Semi-analytic approach

• Trace merger histories with N-body simulations
  (cannot use Press-Schechter because you need to
  know where the galaxies are)
• More massive haloes form earlier longer merger
  history.
• There is also a larger-scale bias haloes of a
  given mass form earlier in denser environments
  (Sheth Tormen 2004 Abbas Sheth 2005 Harker
  et al. 2005)
• Make simple assumptions about gas accretion (e.g.
  no accretion onto satellites) and feedback
  (supernova, AGN)

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General trends successes
Okamoto Nagashima (2003) SFR-radius
Springel et al. 2001 morphology-density relation
0.0 0.5 1.0 1.5 2.0 R/R200
Diaferio et al. (2001) colour-radius
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Bimodality?
Cole et al. 2000 Supernova feedback prescription
does not produce bimodal colour distribution at
faint magnitudes.

• Springel et al. 2001 Diaferio et al. 2001
• Bimodality in field not clear
• All cluster galaxies are red

Data
Model

• Okamoto Nagashima 2003
• SFR is suppressed in all galaxies blue peak is
  distorted

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SPH simulations
But colour-distribution of galaxies doesnt look
quite right

• Keres et al. (2005) SPH simulations reproduce
  trend of decreasing SFR with increasing density
  (see also Berlind et al. 2004).
• Confirm this is due to reduced accretion of hot
  gas

SPH
SFR
Hot accretion
Observed
Cold accretion
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SPH simulations
Observations Blanton et al. (2004)

• Berlind et al.
• Qualitative agreement of environment-age
  (colour?) trends
• Central galaxy mass (luminosity?) correlates with
  halo mass
• Satellite galaxies age (colour) associated with
  mean accretion time
• But colour distribution is still wrong (unimodal)

Contours Galaxy numbers
Contours Local density
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Improving the colour distribution

• Springel, Di Matteo Hernquist (2005)
• Including black hole feedback terminates star
  formation more quickly. Leads to rapid reddening
  of merger remnants

• Sijacki Springel 2005
• AGN feedback removes young population in cD
  galaxies

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Improving the colour distribution

• Croton et al. (2005)
• Radio-feedback most efficient in large groups.
• Proportional to MgasMBH

Cooling rate (Msun/yr)
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Models summary

• 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?

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Back to observations Evolution
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Evolution clusters(briefly)

• Morphology-density relation (see talks by
  Postman, Dressler)
• Fewer S0 in z1 clusters, but non-zero
• Little evolution in MDR z1 to z0.5
• Suggests high-z MDR is primordial, with zlt0.5
  environment-driven evolution
• SFR and colour gradients
• Radial gradients steeper in the past (Ellingson
  et al. 2001 Kodama Bower 2001)
• Can be related to truncation of star formation in
  an infalling field population

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Clusters

• Tanaka et al. 2005 (see poster)
• tight CMR in place in clusters to z0.8
• Faint end of CMR in groups formed z0.5
• No CMR in field at z0.8
• Also De Lucia (2004) faint end of red sequence
  disappears at zgt0.5

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Cluster galaxy evolution

• Supported by observed evolution in OII-emission
  fraction (Nakata et al. 2005)
• Field evolves much more strongly than clusters
  (for bright galaxies)

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Cluster galaxy evolution

• Complete Ha studies emission line fraction
  depends more strongly on cluster mass than on
  redshift.

Finn et al. 2005.
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Evolution photo-z surveys

• Similar rate of increase in red fraction in the
  field and clusters
• average field red sequence galaxy came into the
  sample later

Red galaxy fraction
High density
All galaxies
Red galaxy fraction 0 0.2 0.4 0.6 0.8 1.0
0.2 0.4 0.6 0.8
Low density
MV lt -20
Redshift
COMBO-17 E. Bell et al.
CFHTLS Nuijten et al. (2005)
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Luminosity, density and redshift dependence of
red fraction
RCS zgt0 Yee et al. (2005)
SDSS z0 Balogh et al. (2004)
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Luminosity, density and redshift dependence of
colour
RCS zgt0 Yee et al. (2005)
SDSS z0 Balogh et al. (2004)
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Luminosity, density and redshift dependence of
colour

• Little evolution in red peak colour

RCS zgt0 Yee et al. (2005)
SDSS z0 Balogh et al. (2004)
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Luminosity, density and redshift dependence of
colour

• Little evolution in red peak colour
• Colours of bright blue galaxies evolve strongly

RCS zgt0 Yee et al. (2005)
SDSS z0 Balogh et al. (2004)
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Galaxy groups at z0.4

• Selected from CNOC2 survey
• gt30 nights Magellan spectroscopy (better
  completeness, depth)
• ACS image of 30 groups
• GALEX data rolling in slowly
• Spitzer (IRAC and shallow MIPS) data from GTO
  programs
• Collaborators Dave Wilman (MPE), Richard Bower
  (Durham), Gus Oemler, John Mulchaey (Carnegie),
  Ray Carlberg (Toronto)

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Groups at z0.4 Morphologies
E/S0-dominated group s226 km/s

• Spiral-dominated group
• s270 km/s

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Morphologies early results

• There are fewer spiral galaxies in groups than in
  the field, at the same redshift.
• No evidence for more disturbance/irregularities
  in group galaxies

Groups
E/S0 fraction
Field
Field
Spiral fraction
Spiral fraction
Groups
Groups
Vel. Dispersion (km/s)
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• The connection between star formation rate,
  morphology and environment

Field
Groups
Distributions are corrected for differences in
luminosity function between group and field
S0
Elliptical
Early spiral
Late spiral
Like clusters, groups contain passive spirals
disk morphology but low star formation rates
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Stellar mass-SFR
Rosati? z1
SDSS (Kauffmann et al.)

• Stellar masses from archival Spitzer (IRAC) data
• Significant star formation seen in more massive
  galaxies than locally downsizing?
• No significant difference between group and field
  for this subsample.

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Evolution in groups

• Use OII equivalent width to find fraction of
  galaxies without significant star formation
• most galaxies in groups at z0.4 have significant
  star formation in contrast with local groups
• cf. Gonzalez talk supergroup

Fraction of non-SF galaxies
Wilman et al. (2004)
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Group SFR evolution
Groups

• Fraction of non-SF galaxies increases with
  redshift
• for both groups and field
• Insensitive to aperture effects
• Evolution cannot be account for by
  passive-evolution models. Require truncation of
  star formation (both groups and field)

Fraction of non-SF galaxies
Field
Fraction of non-SF galaxies
Wilman et al. 2004
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Group Evolution
Groups Wilman et al. (2005)
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Group SFR evolution

• shape of OII distribution evolves with redshift
  but does not depend on environment
• Result sensitive to aperture effects

Wilman et al. 2004
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High redshift

• Spectroscopic survey 100 redshifts 1.48ltzlt2.89
• Overdense region has more massive, older galaxies
• Consistent with expectations for earlier
  formation time (1600 Myr vs 800 Myr)

Steidel et al. (2005)
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High redshift

• UV-selected LBG survey
• No environmental dependence of SFR
• Can be consistent cluster galaxies get head
  start, but instantaneous SFR the same
• Even at z0 it seems star-forming galaxies have a
  distribution independent of environment

Bouché Lowenthal (2005)
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The future

• Theory still has a lot of catching up to do
• Thus we are in discovery mode rather than testing
  mode
• Observations
• Dust-obscured SF (Spitzer, Herschel)
• AGN/SF connection at zgt0
• Lower luminosities
• Spatial dependence of SFR (i.e. IFU spectroscopy)
• Transitional galaxies