The Distribution of Baryons in Galaxy Clusters and Groups
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Transcript of The Distribution of Baryons in Galaxy Clusters and Groups
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The Distribution of Baryons in Galaxy Clusters
and GroupsAnthony Gonzalez
University of Florida
Dennis Zaritsky, Ann ZabludoffUniversity of Arizona
Ohio State University, September 2007
Cosmology and Galaxy Structure from Extreme Galaxies
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Intracluster Light
What is Intracluster Light (ICL)?• 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 Chemical Enrichment of the ICM
The Structure of Galaxies
Evolution of the Cluster Galaxy Populations
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Intracluster Light
Evidence for Intracluster Light (ICL)?• Intracluster planetary nebulae and globular clusters in Virgo
– Feldmeier et al. (2003,2004)– Williams et al. (2007)
• Extended excess surface brightness relative to central BCG profile
• Rising velocity dispersion profiles around BCGs – Dressler (1979), Carter et al. (1985), – Kelson et al. (2002)
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Intracluster Light: A definition
Evidence for Intracluster Light (ICL)?• Intracluster planetary nebulae in Virgo
– Feldmeier et al.
• Extended excess surface brightness relative to central BCG profile
• Rising velocity dispersion profiles around BCGs– Dressler (1979), Carter et al. (1985), – Kelson et al. (2002)
BCG and ICL
Galaxies
Kelson et al. 2002
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Intracluster Light
What do we know?• 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
• 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
• 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)
• Full 2D profile modelling with GALFIT
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Final Data Quality• Initial sky level: I≈20 mag arcsec-2
• Systematic uncertainty (5): I≈27.5 mag arcsec-2
• Equivalent physical radius: r ≈ 200-600 h70-1 kpc
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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 2955
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Sharp breaks in ellipticity and PA
Single deV (r1/4)
Abell 2571: An Example
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Sharp breaks in ellipticity and PA
Single Sersic (r1/n)
Abell 2571: An Example
deV – Sersic
Avg 2= 3650 (1 dof)
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Abell 2571: An Example
• BCG, ICL profiles separable
• ~80% of combined luminosity is in ICL
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Are galaxy clusters fair samples of the universe?
Do we see all the expected baryons?
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
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Baryon Budget: Theoretical Expectations
• What does one expect:– Roughly constant baryon
fraction with mass
– Some offset from WMAP baryon fraction
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Kravtsov et al. 2005
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Ettori et al. 2006
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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
Kravtsov et al. 2005
Gas
Stars
Ettori et al. 2006
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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
Vikhlinin et al. 2006
Lin, Mohr, & Stanford 2003
Is the baryon census complete?
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A New Census of Stellar Baryons Including the ICL
• 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
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Tools for the Census...
Prerequisites– Cluster Radius
– Cluster Mass
r200
r500
r2500
23’
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Tools for the Census...
Prerequisites– Cluster Radius
• X-ray data generally lacking for sample
• Calibrate -r500 and -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 -M500 relation using subset of Vikhlinin et al. sample
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Tools for the Census...
-M500 relation• Published dispersions for
subset of Vikhlinin clusters• Calibrated for >500 km/s
For total baryon fraction we will focus upon range where the relation is calibrated.
Gonzalez et al. 2007
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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
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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
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Total Stellar Mass
Steep decline in stellar baryon fraction with cluster mass.
log(f*,500)= 7.57 - 0.64 log(M500)
Gonzalez et al. 92007)Gonzalez et al. (2007)
1014 1015
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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)
Gonzalez et al. (2007)
1014 1015
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Total Baryon Fraction
• Baryon fraction flat with massTrade-off between stellar and ICM
baryons.
Star formation more efficient in lower mass systems
Gonzalez et al. (2007)
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Total Baryon Fraction
• Total is 76% of WMAP value Possible ExplanationsSystematics
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 IncorrectSee McCarthy et al. 2006
Gonzalez et al. (2007)
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What do our results imply for the origin of the intracluster light?
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
Evolution of the Cluster Galaxy Populations
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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)
log (Msun)
MB
CG
+IC
LL
ICL/(
LB
CG+
LIC
L)
Conroy et al. 2007
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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
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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. Selection Bias?
Purcell et al. 2007
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Does intracluster light lie on the fundamental plane?
How can extreme systems shed light on galaxy structure?
Intracluster Light & Brightest Cluster Galaxies
Counting Baryons
The Structure of GalaxiesEvolution of the Cluster
Galaxy Populations
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The Fundamental Plane
Basic Expectation: Virial Equilibrium
2+GM/re = 0 → 2 ~ (M/L)(Iere2)/re
log re = 2 log – 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 – 0.77 log Ie + C (Bernardi et al 2003)
Does the cluster spheroid (CSph = ICL or BCG+ICL) obey a similar relation?
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The CSph Fundamental Plane
• Tight Correlation (rms=0.074 for BCG+ICL)
• Smaller A than for ellipticals
ICL BCG+ICL BCG+ICL+Galaxies
Zaritsky, Gonzalez, & Zabludoff (2006a)
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Comparison to other Spheroids
• CSph (this work)
• BCGs (Oegerle & Hoessel 1992)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 – log Ie – log (M/L) + C
Zaritsky, Gonzalez, & Zabludoff (2006a)
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What is driving change in “A”?
• 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)dSph (assorted)
M/L variationsToo large for stellar populationsNot described by power law
Zaritsky, Gonzalez, & Zabludoff (2006a)
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What is driving change in “A”?
Assume log M/L ~ ( log – )2
Not unique, but sufficient
Dwarf spheroids not included in fit
log re = -2 log2 +2(1+)log +B log Ie +C
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van den Bosch et al. (2007)
Zaritsky, Gonzalez, & Zabludoff (2006a)
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The Fundamental Manifold
rms = 0.099 (Not much worse than individual FPs.)
Fundamental Plane Fundamental Manifold
dE E
B
CG
CSph
Zaritsky, Gonzalez, & Zabludoff (2006a)
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The other extreme…Zaritsky, Gonzalez, & Zabludoff (2006b)
LG Dwarfs lie on same FM.
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Towards a General Equation of Galactic Structure
• Can we do something similar for all galaxies?If we define V2= (1/2) vc
2 + 2, 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.
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•Large scatter in projection
• Only 24% scatter about second order fit in log V, log Ie
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• Good agreement between dynamical and best-fit M/L
log re = log V2 - log Ie - log L + log A - log B +C
Use Cappellari et al. (2006) SAURON data to solve for constants
Cappellari et al.
Walker et al. (dSph)
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Reduced Equation of Galactic Structure
Scatter is 0.093 M/L is main driver for observed variation Other factors secondary
(environment, AGN, accretion history,…)
Jorgensen et al. (1996)
Springob et al. (2007)
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Intracluster Light & Brightest Cluster Galaxies
Counting Baryons Chemical Enrichment of the ICM
The Structure of Galaxies
Evolution of the Cluster Galaxy Populations
Summary and Conclusions