Transcript Driving downsizing with galaxy groups

Driving Downsizing with groups
of galaxies
Michael Balogh
Department of Physics and Astronomy
University of Waterloo
or: the faint red galaxy problem
Collaborators
David Gilbank, Sean McGee, Robbie Henderson (Waterloo)
Dave Wilman, Daniel Pierini (MPE, Garching)
Richard Bower, Simon Morris (Durham)
John Mulchaey, Gus Oemler (Carnegie)
Outline
I. Review: Galaxy formation models
II. Evolution of faint red galaxies
III. Galaxy groups at z=0.4
IV. Revisiting starvation
The halo model
• The growth of
dark matter
structure is now
well understood
• Galaxy formation
history is tightly
coupled to dark
matter halo mass
www.nbody.net
The halo model
Hot baryons
~106 K for
galaxies, hence
invisible
Radiative
cooling
Dark matter
The inefficiency of star formation
Wstars= 0.0014 ± 0.00013
Wstars/ Wbaryon =0.03
(Balogh et al. 2001; Cole et al. 2002)
 >95% of baryons are dark
Galaxy Luminosity Function
Number density of galaxies
Theory
Benson et al. 2003
Data
Wstars/ Wbaryon =0.03
(Balogh et al. 2001; Cole et al. 2002)
Luminosity
Stellar mass
• Blue galaxies are absent above ~3x1010 MSun
• Star formation today occurs in low-mass
galaxies
Kauffmann et al. (2003)
Baldry et al. (2004)
11
10
9
log M*
8
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
Galaxy Clusters
• A standard picture to motivate environmental
effects:
 Clusters are dominated by bright, red ellipticals
Low-mass galaxies
• Galaxies with M~109 MSun are well below
the “threshold” mass.
• But the fraction of red galaxies STILL
depends strongly on environment.
Baldry et al. (2006)
Strangulation/Starvation
Kenney et al. 2003
Vollmer et al. 2004
• Gas around satellite galaxies may
be shock-heated, tidally- or rampressure stripped
• Stripping the cold, dense gas in
the disk requires high velocities
and ICM densities
• The hot halo can perhaps be
stripped more easily (Larson,
Tinsley & Caldwell 1980)
Kawata & Mulchaey 2007
Environment: models
• Standard assumption is that satellite
galaxies instantly lose their entire hot
halo.
 SFR then declines on a typical timescale
(Balogh, Navarro & Morris 2000):
 M* 
t  2.2 10

10
M
Sun 

0.3
Gyr
• Low stellar-mass, red
galaxies are predicted to
be in groups, above the
critical mass limit
Satellite galaxies at z=0
• Most faint, satellite galaxies are blue
• Models too efficient at shutting off gas
supply?


Model predictions
Weinmann et al. 2006
Too rapid? Too complete?
Or should this mechanism only apply to
massive haloes?
Part II:
Evolution of faint red galaxies
Red Galaxy luminosity function
• Faint red galaxies have
appeared recently in
clusters
• Dwarfs: -18.2>Mv>-20
• Giants Mv<-20
De Lucia et al. (2007)
Red Dwarfs/Giants
• Faint red galaxies have built up in
clusters since z~1
Cluster data from:
Gilbank et al. (2007)
Stott et al. (2007)
Hansen et al. (2007)
Barkhouse et al. (2007)
Andreon (2007)
Tanaka et al. (2005)
De Lucia et al. (2004)
Gilbank & Balogh (2008)
Redshift
Red Dwarfs/Giants
• Faint red galaxies are less common in
the field – but also increasing with
time (more rapidly?)
Field data from:
Bell et al. (2003, 2004)
Driver et al. (2006)
Scarlata et al. (2007)
Brown et al. (2007)
Zucca et al. (2006)
Baldry et al. (2004)
Gilbank & Balogh (2008)
Redshift
• Models predict a large fraction of faint, red
galaxies at all redshifts, even in the field
• Due to the red satellite galaxies in small groups
Red Dwarfs/Giants
Bower et al. (2006) model predictions
Gilbank & Balogh (2008)
Redshift
Red Dwarfs/Giants
• The evolution in the field can be explained if faint,
red galaxies are produced only in groups with
masses greater than 1012.5 MSun.
1013 M Sun
1012.5 M Sun
1012 M Sun
Gilbank & Balogh (2008)
Redshift
• Models are far
too efficient at
quenching star
formation in
satellite (group)
galaxies
Red Dwarfs/Giants
Red dwarf/giant ratio
Redshift
• Galaxy groups at z=0.5 are critical for
detailed study of transforming galaxies
Part III:
Galaxy groups at z=0.4
Groups at z~0.4
•
•
•
•
•
•
•
~200 groups
between z~0.1
and z~0.55,
selected from
the CNOC2
survey (Carlberg
et al. 2001)
Follow-up at Magellan
26 groups targeted between z
=0.3 and z=0.55
Observations of 20 groups for
1 orbit each in F775W filter
with HST ACS camera
3 Orbit GALEX data
IRAC and MIPS data
XMM, Chandra
Millennium Simulation
All haloes
“CNOC2” Groups
Z=0.5
McGee et al. 2007
• At all stellar
masses, starforming
galaxies are
found less
frequently in
groups
Fraction with [OII] emission lines
Star formation in groups
Balogh et al. 2006
Passive galaxies
• Spitzer IRAC colours are an
excellent tracer of low-levels
of activity
E/S0
Spirals
lrest [mm]
[8mm]-[3.6mm] colour
Wilman et al. 2007
Star formation in groups
• Dusty and/or low-levels of star formation in massive galaxies
10.5
Wilman et al. 2007
11
log10 Mstellar/MSun
11.5
Optically Active fraction
Break occurs at ~1011 MSun.
Group galaxies still show less activity than field galaxies of
the same mass.
Infrared Active fraction


Balogh et al. 2006
Group morphologies
• Only a small difference in galaxy morphology at z=0.4
This evolves strongly to z=0
Suggest morphological transformation may lag behind star
formation quenching
CNOC2
Fraction of disk galaxies
Fraction of disk galaxies


McGee et al. 2007
MGC
Allen et al. 2006
Passive spirals
• Moran et al. (2007) analyse
GALEX colours of passive
spirals in two rich clusters at
z=0.5
• “starved” spirals appear to be
found in infalling groups
GALEX
• Starvation model seems a good fit to
the passive spirals in CNOC2 groups
Red: passive spirals
Black: normal spirals
CNOC2 groups
Green: passive spirals
Blue: normal spirals
McGee et al. in prep
Summary: z=0.4 groups
• There is evidence galaxies are being
quenched in groups, but the effect is
not dramatic
• We are embarking on a full
multiwavelength analysis from FUV to
MIR to constrain the star formation
histories of group members
Part IV:
Revisiting starvation models
Slow strangulation
• How quickly do galaxies lose their gas?
• Consider analytic and numerical (GADGET2) models of “hot” gas+DM haloes merging
with groups or clusters, on cosmologically
sensible orbits.
McCarthy et al. 2007
Hot stripping in a uniform
medium
• Instantaneous
stripping: a
fixed fraction
of gas will be
removed
McCarthy et al. 2007
Hot stripping in a uniform
medium
• Instantaneous
stripping: a
fixed fraction
of gas will be
removed
• In reality
there is a
delay of ~1
Gyr which we
model linearly:
M 
t
 cs
Dark matter
Gas
Analytic prediction
McCarthy et al. 2007
Hot stripping in clusters
• Onset of stripping is delayed
• a=2, =2/3 works well for a
variety of orbits, mass ratios.
• Takes ~2 Gyr to remove half the
gas mass
 Still plenty of hot fuel left
 The amount of gas left depends on
orbit, mass ratio etc., but the time
delay of at least 1-2 Gyr is fairly
robust
• Through starvation alone, lowmass satellite galaxies could
potentially continue star
formation for a significant
fraction of a Hubble time.
McCarthy et al. 2007
Observational evidence
• Sun et al. (2007) detect hot coronae around galaxies in
clusters

Reduced luminosity compared with isolated galaxies, but still
significant.
Summary
• There are environmental influences on
galaxy formation after z=1
• Probably dominant in massive groups, not
clusters.
• Current modeling of environmental effects
is wrong and this has consequences for
predictions of the general field (which is
dominated by groups)
 Simple strangulation models may still work
well, if the instantaneous assumption is
dropped.
Extra slides
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)
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 )
Evolution in Groups
• SFH of
galaxies in
groups are
similar to the
field, and
evolve with it
Wilman et al. 2005
Groups - morphology
• Use Gim2D to
measure the
fraction of light in
the bulge (B/T)
• Low-z data from
the MGC (Driver
et al.)
• Models do well
here.
 Merger history
OK. SFH needs
work.
McGee et al. 2007
Black: data
Red: models