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

The influence of environment
on galaxy populations
Michael Balogh
University of Waterloo, Canada
Outline
• Low redshift
– Simple trends encompass most of what we know
of as environmental influences
• Models: what works and what doesn’t
• Redshift evolution
• The future: what’s next?
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
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?
– Today’s population is the result of different
environments at different epochs: cannot try to
isolate one mechanism as responsible for the
observed trends.
The local Universe
Colour-magnitude distribution
• Nearby galaxies
seem to fall into two
surprisingly welldefined, smoothly
varying distributions.
• Colour, luminosity,
concentration, star
formation rate
Blanton et al. 2004
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.
Bright
Faint
Baldry et al. 2003
(u-r)
• 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
• 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
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
•
•Hard to explain
with simple,
slow-decay
models (e.g.
Balogh et al. 2000)
Rines et al. 2005: Ha distribution in virial,
infall and field regions nearly identical.
Halo mass dependence
R luminosity
• Environment:
halo mass
– Use luminosity as
tracer of mass.
Compare with
theoretical mass
function
[-22,-23]
[-21,-22]
[-20,-21]
[-19,-20]
[-18,-19]
• At fixed mass the
late-fraction
depends weakly
on luminosity
• Late-type fraction
depends most
strongly on halo
mass
Weinmann et al. 2005
Halo mass dependence
colour
[-22,-23]
[-21,-22]
[-20,-21]
[-19,-20]
[-18,-19]
SFR
• Average
properties of
galaxies in either
peak is
independent of
halo mass
R luminosity
concentration
– But depends on
luminosity
Weinmann et al. 2005
Local effects?
• Still a (weak)
trend with radius
in haloes of
fixed mass
• Dependence on
luminosity
(surprisingly?)
weak
1014<M<1015
1013<M<1014
Weinmann et al. 2005
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 Eke’s talk.
Definition of central?
Implications
•
•
Simple dependence of “late-type” fraction
on environment characterizes much of
observed trends (e.g. SFR-density,
morphology-density, colour-density etc.).
Interpretation?
1. Two modes of formation. Within each peak is
variance due to dust, metallicity (second-order
effects).
2. Transitions: Where do S0, E+A fit in?
3. Burst vs. continuous SFR (Kauffmann et al.
2005)
Signs of Nurture: Virgo
spirals
• Ram-pressure stripping
in Virgo
Kenney et al. 2003
Vollmer et al. 2004
• Truncated Ha disks in
clusters
Ha for Virgo galaxy
Ha for normal galaxy
Koopmann & Kenney 2004
also: Vogt et al. 2004
Signs of Nurture: morphology
and SFR
•
•
•
•
Passive Spirals
E+A galaxies?
S0, dSph, UCDs
Wolf ’s 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
AGN
• AGN fraction independent of density
– Surprising?
Miller et al. (2003)
Carter et al. (2001)
Models
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)
General trends: successes
Okamoto & Nagashima (2003)
SFR-radius
0.0
Diaferio et
al. (2001)
colourradius
0.5
1.0
1.5
R/R200
Springel et al. 2001: morphology-density relation
2.0
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
cluster
Spirals
Ellipticals
All
Okamoto & Nagashima 2003
–SFR is suppressed in all
galaxies: blue peak is
distorted
-24 -22 -20 -18 -16
-24 -22 -20 -18 -16
MV-logh
MV-logh
SPH simulations
But colour-distribution of
galaxies doesn’t 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
Cold accretion
Observe
d
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
BH accretion rate
Magorrian-AGN
No feedback
• Sijacki & Springel 2005
• AGN feedback removes
young population in cD
galaxies
Improving the colour
distribution
Cooling rate (Msun/yr)
• Croton et al. (2005)
• Radio-feedback most efficient
in large groups.
• Proportional to Mgas×MBH
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?
Back to observations:
Evolution
Evolution: clusters
(briefly)
• Morphology-density relation (see talks by Postman,
Dressler)
– Fewer S0 in z=1 clusters, but non-zero
– Little evolution in MDR z=1 to z=0.5
– Suggests high-z MDR is primordial, with z<0.5
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
Clusters
•
Tanaka et al. 2005 (see poster)
– tight CMR in place in clusters to z=0.8
– Faint end of CMR in groups formed z~0.5
– No CMR in field at z=0.8
– Also De Lucia (2004): faint end of red sequence disappears at
z>0.5
Cluster galaxy evolution
• Supported by observed evolution in [OII]emission fraction (Nakata et al. 2005)
Field
– Field evolves much more strongly than
clusters (for bright galaxies)
2dF
Clusters
Nakata et al. 2005
Postman, Lubin & Oke 2001
van Dokkum et al. 2000
Fisher et al. 1998
Czoske et al. 2001
Evolution: photo-z surveys
0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8 1.0
Red galaxy fraction
– average field red sequence
galaxy came into the sample
later
Red galaxy fraction
• Similar rate of increase in red
fraction in the field and clusters
High density
MV < -20
All galaxies
Low density
Redshift
COMBO-17: E. Bell et al.
CFHTLS: Nuijten et al. (2005)
Luminosity, density and redshift
dependence of red fraction
SDSS z=0: Balogh et al. (2004)
RCS z>0: Yee et al. (2005)
Luminosity, density and
redshift dependence of colour
RCS z>0: Yee et al. (2005)
Luminosity, density and
redshift dependence of colour
• Little evolution in red peak colour
RCS z>0: Yee et al. (2005)
Luminosity, density and
redshift dependence of colour
• Little evolution in red peak colour
• Colours of bright blue galaxies evolve strongly
RCS z>0: Yee et al. (2005)
Galaxy groups at z=0.4
• Selected from CNOC2 survey
• >30 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)
Groups at z=0.4: Morphologies
E/S0-dominated
group
s=226 km/s
Spiral-dominated
group
s=270 km/s
E/S0 fraction
Morphologies: early results
Groups
• There are fewer spiral galaxies in
groups than in the field, at the same
redshift.
• No evidence for more
disturbance/irregularities in group
galaxies
Field
Spiral fraction
Spiral fraction
Field
Groups
Groups
Vel. Dispersion (km/s)
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
Stellar mass-SFR
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.
Rosati? z=1
Fraction of non-SF galaxies
Evolution in groups
• Use [OII] equivalent width to
find fraction of galaxies
without significant star
formation
• most galaxies in groups
at z~0.4 have significant
star formation – in
contrast with local
groups
• cf. Gonzalez talk:
supergroup
Wilman et al. (2004)
Group SFR evolution
Groups
Fraction of non-SF galaxies
• Fraction of non-SF galaxies
increases with redshift
• for both groups and field
• Insensitive to aperture effects
Fraction of non-SF galaxies
Field
• Evolution cannot be account
for by passive-evolution models.
Require truncation of star
formation (both groups and
field)
Wilman et al. 2004
Group Evolution
Groups: Wilman et al. (2005)
Field
Nakata et al. 2005
Postman, Lubin & Oke 2001
van Dokkum et al. 2000
2dF
Clusters
Fisher et al. 1998
Czoske et al. 2001
High redshift
• Spectroscopic survey: ~100 redshifts 1.48<z<2.89
• Overdense region has more massive, older galaxies
• Consistent with expectations for earlier formation time (1600 Myr vs 800
Myr)
Steidel et al. (2005)
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 z=0 it seems
star-forming galaxies
have a distribution
independent of
environment
Bouché & Lowenthal (2005)
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 z>0
Lower luminosities
Spatial dependence of SFR (i.e. IFU
spectroscopy)
– Transitional galaxies