Cosmology and Galaxy Structure from Extreme Galaxies
The Distribution of Baryons in
Galaxy Clusters and Groups
Anthony Gonzalez
University of Florida
Dennis Zaritsky, Ann Zabludoff
University of Arizona
Ohio State University, September 2007
Intracluster Light
What is Intracluster Light (ICL)?
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Free-floating stars bound only to cluster potential
Originally postulated to exist by Zwicky
Also known as intracluster stars (ICS)
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Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Evolution of the Cluster
Galaxy Populations
Chemical Enrichment of the ICM
The Structure of Galaxies
Intracluster Light
Evidence for Intracluster Light (ICL)?
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Intracluster planetary nebulae and globular clusters in Virgo
– Feldmeier et al. (2003,2004)
– Williams et al. (2007)
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Extended excess surface brightness relative to central BCG profile
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Rising velocity dispersion profiles around BCGs
– Dressler (1979), Carter et al. (1985),
– Kelson et al. (2002)
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Kelson et al. 2002
Galaxies
Intracluster Light: A definition
Evidence for Intracluster Light (ICL)?
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Intracluster planetary nebulae in Virgo
– Feldmeier et al.
BCG and ICL
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Extended excess surface brightness relative to central BCG profile
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Rising velocity dispersion profiles around BCGs
– Dressler (1979), Carter et al. (1985),
– Kelson et al. (2002)
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Intracluster Light
What do we know?
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Prevailing view: ICL contains non-negligible fraction of stars in all clusters
Can be generated by mergers and tidal stripping; produced in current simulations
But...quantifying total contribution of ICL challenging due to low SB
Open questions...
– Fraction of light/baryons in ICL
– Structure and Distribution of ICL
– ICL properties vs. cluster mass and radius
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Our work, the first step...
An intracluster light survey
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Highly uniform data
– Drift scan imaging from LCO 1m (300-1000s) in Gunn I
– 30 Abell/APM clusters (150-1050 km/s) at z=0.03-0.13
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Reduction techniques optimized for low surface brightness photometry
– Flatness variations <0.2%
– Efficient removal of all other sources of flux
• Other stars/galaxies
• Extended PSFs of saturated stars
• Large scale sky gradients (>> size of BCG)
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Full 2D profile modelling with GALFIT
Final Data Quality
• Initial sky level:
• Systematic uncertainty (5s):
mI≈20 mag arcsec-2
mI≈27.5 mag arcsec-2
• Equivalent physical radius:
r ≈ 200-600 h70-1 kpc
Abell 2955
An Illustration
Series of images here showing A2955 in the
original, star-subtracted, and wavelet image.
Put on a label saying what the limiting sb level is in the
wavelet image, and a rough estimate of the scale
Abell 2571: An Example
Sharp breaks in
ellipticity and PA
Single deV (r1/4)
Abell 2571: An Example
Sharp breaks in
ellipticity and PA
deV – Sersic
Avg Dc2= 3650 (1 dof)
Single Sersic (r1/n)
Abell 2571: An Example
• BCG, ICL profiles separable
• ~80% of combined luminosity
is in ICL
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Are galaxy clusters fair samples of the universe?
Do we see all the expected baryons?
Baryon Budget:
Theoretical Expectations
• What does one expect:
Ettori
et al.et2006
Kravtsov
al. 2005
– Roughly constant baryon
fraction with mass
– Some offset from WMAP
baryon fraction
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Theoretical Expectations
• What does one expect:
– Roughly constant baryon
fraction with mass
– Some offset from WMAP
baryon fraction
– Stellar baryons more
centrally concentrated
than gas
Ettori et al. 2006
Kravtsov et al. 2005
Gas
Stars
Observational Constraints
• What does one see:
– Increasing gas fraction
(fg)with cluster mass
– Increasing total baryon
fraction (fg + f*) with M200
– Limited information about
radial dependence of total
baryon fraction
Is the baryon census complete?
Vikhlinin et al. 2006
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Lin, Mohr, & Stanford 2003
A New Census of
Stellar Baryons Including the ICL
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Specific objectives
– Relative importance of ICL and galaxies
• Stellar baryon fraction
• Distribution of stellar baryons
• Dependence upon halo mass
– Total baryon fraction
• Dependence upon halo mass
• X-ray data do not exist for most of our sample,
so this must be done using published relations
Tools for the Census...
r200
Prerequisites
– Cluster Radius
r500
r2500
– Cluster Mass
23’
Tools for the Census...
Prerequisites
– Cluster Radius
• X-ray data generally lacking for sample
• Calibrate s-r500 and s-r200 using subsets of Vikhlinin et al. and
Arnaud et al. samples
– Cross-check using Hansen et al. (2005) approach to directly
measure galaxy overdensity relative to field
– Cluster Mass
• Velocity dispersions for 23 clusters in sample
• Calibrate a s-M500 relation using subset of Vikhlinin et al.
sample
Tools for the Census...
s-M500 relation
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Published dispersions for
subset of Vikhlinin clusters
Calibrated for s>500 km/s
For total baryon fraction we will
focus upon range where the
relation is calibrated.
Gonzalez et al. 2007
Stellar Baryon Distribution vs. Mass
Gonzalez et al. 2007
• Highest BCG+ICL fractions
found in lowest mass systems.
– Several possible interpretations
– Selection biases potentially
important
“Intracluster” light can be efficiently
generated in groups.
Selection Bias?
Total Stellar Mass
• Luminosity Stellar mass
– Using SAURON results
– Luminosity-weighted M/L for L>0.25 L*
– <M/LI> =3.6 for typical Schechter LF
• Cautionary Notes
– Use elliptical M/L for all galaxies
– Assume same M/L for BCG+ICL
Cappellari et al. 2006
Total Stellar Mass
Steep decline in stellar baryon
fraction with cluster mass.
log(f*,500)= 7.57 - 0.64 log(M500)
1014
1015
Gonzalez et al. Gonzalez
92007) et al. (2007)
Total Gas Mass
Gas masses from Vikhlinin 2006
– No overlap with our sample
– More restricted mass range
(augment at low mass with
Gastaldello et al. 2006)
log(f*,500)= 7.57 - 0.64 log(M500)
log(fg,500)= -3.87 + 0.20 log(M500)
1014
1015
Gonzalez et al. (2007)
Total Baryon Fraction
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Baryon fraction flat with mass
Trade-off between stellar and ICM
baryons.
Star formation more efficient in lower
mass systems
Gonzalez et al. (2007)
Total Baryon Fraction
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Total is 76% of WMAP value
Possible Explanations
Systematics
X-ray mass & gas fraction (~15%)
Zhang et al. data  85% WMAP
Physics
Simulations predict baryon
depletion within r500 (~10%)
Missing Baryons
Must be independent of M500.
No compelling evidence currently.
WMAP Incorrect
See McCarthy et al. 2006
Gonzalez et al. (2007)
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Evolution of the Cluster
Galaxy Populations
What do our results imply for the origin of the intracluster light?
Underlying
Physics
A simple picture that works
– Bulk of ICL from disrupted
galaxies
– >80% of stars in disrupted galaxies
go into ICL
• (Sat2Cen model in Figure)
LICL/(LBCG+LICL)
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MBCG+ICL
Conroy et al. 2007
log (Msun)
Stellar Baryon Distribution vs. Mass
• Highest BCG+ICL fractions
found in lowest mass systems.
– Several possible interpretations
– Selection biases potentially
important
“Intracluster” light can be efficiently
generated in groups.
Selection Bias?
Gonzalez et al. 2007
Stellar Baryon Distribution vs. Mass
• Highest BCG+ICL fractions
found in lowest mass systems.
– Simulations predict behavior
similar to data
“Intracluster” light can be efficiently
generated in groups.
Purcell et al. 2007
Selection Bias?
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Evolution of the Cluster
Galaxy Populations
The Structure of Galaxies
Does intracluster light lie on the fundamental plane?
How can extreme systems shed light on galaxy structure?
The Fundamental Plane
Basic Expectation: Virial Equilibrium
s2+GM/re = 0
→
s2 ~ (M/L)(Iere2)/re
log re = 2 log s – log Ie – log (M/L) + C
General Observation for Ellipticals
– Very tight relation (Fundamental Plane, rms=0.085)
– Tilted relative to virial expectation
log re = 1.21 log s – 0.77 log Ie + C (Bernardi et al 2003)
Does the cluster spheroid (CSph = ICL or BCG+ICL) obey a
similar relation?
The CSph Fundamental Plane
ICL
BCG+ICL
Zaritsky, Gonzalez, & Zabludoff (2006a)
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Tight Correlation (rms=0.074 for BCG+ICL)
Smaller A than for ellipticals
BCG+ICL
+Galaxies
Comparison to other Spheroids
Zaritsky, Gonzalez, & Zabludoff (2006a)
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CSph (this work)
BCGs (Oegerle & Hoessel 1992)
E (Jorgensen et al. 1996)
E/dE (Matkovic & Guzman 2005)
E/dE/dSph (Bender et al. 1991)
dE (Geha et al.)
log re = 2 log s – log Ie – log (M/L) + C
What is driving change in “A”?
Zaritsky, Gonzalez, & Zabludoff (2006a)
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CSph (this work)
BCGs (Oegerle & Hoessel 1992)
E (Jorgensen et al. 1996)
E/dE (Matkovic & Guzman 2005)
E/dE/dSph (Bender et al. 1991)
dE (Geha et al.)
dSph (assorted)
M/L variations
Too large for stellar populations
Not described by power law
What is driving change in “A”?
Zaritsky, Gonzalez, & Zabludoff (2006a)
(a log s – b)2
Not unique, but sufficient
van den
Bosch etlog
al. (2007)
Assume
M/L ~
Dwarf spheroids not included in fit
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log re = -a2 log2 s +2(1+ab)log s +B log Ie +C
The Fundamental Manifold
Zaritsky, Gonzalez, & Zabludoff (2006a)
Fundamental Plane
Fundamental Manifold
rms = 0.099 (Not much worse than individual FPs.)
The other extreme…
Zaritsky, Gonzalez, & Zabludoff (2006b)
LG Dwarfs lie on same FM.
Towards a General Equation of Galactic
Structure
• Can we do something similar for all galaxies?
If we define V2= (1/2) vc2 + s2, for an isothermal sphere the virial eq. is:
AV2=B GM/r
which yields:
log re = log V2 - log Ie - log L + log A - log B +C
Assume all variation is in M/L rather than A,B and fit data for M/L.
We use the Pizagno et al. (2006), Springob et al. (2007), Geha et
al. (2006) spiral samples.
•Large scatter in projection
• Only 24% scatter about
second order fit in log V, log Ie
log re = log V2 - log Ie - log L + log A - log B +C
Use Cappellari et al. (2006) SAURON data to solve for constants
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Walker et al. (dSph)
Good agreement between
dynamical and best-fit M/L
Cappellari et al.
Reduced Equation of Galactic Structure
Jorgensen et al. (1996)
Springob et al. (2007)
Scatter is 0.093  M/L is main driver for observed variation
 Other factors secondary
(environment, AGN, accretion history,…)
Summary and Conclusions
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Evolution of the Cluster
Galaxy Populations
Chemical Enrichment of the ICM
The Structure of Galaxies