The Distribution of Baryons in Galaxy Clusters and Groups

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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)

Intracluster Light & Brightest Cluster Galaxies

Counting Baryons Chemical Enrichment of the ICM

The Structure of Galaxies

Evolution of the Cluster Galaxy Populations



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)



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



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

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

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

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

Sharp breaks in ellipticity and PA

Single deV (r1/4)

Abell 2571: An Example

Sharp breaks in ellipticity and PA

Single Sersic (r1/n)


deV – Sersic

Avg 2= 3650 (1 dof)


• BCG, ICL profiles separable

• ~80% of combined luminosity is in ICL

Are galaxy clusters fair samples of the universe?

Do we see all the expected baryons?


Counting Baryons

Baryon Budget: Theoretical Expectations

• What does one expect:– Roughly constant baryon

fraction with mass

– Some offset from WMAP baryon fraction



Kravtsov et al. 2005



Ettori et al. 2006

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



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?

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

Tools for the Census...

Prerequisites– Cluster Radius

– Cluster Mass

r200

r500

r2500

23’


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


-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

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?


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)

Gonzalez et al. 92007)Gonzalez et al. (2007)

1014 1015

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

Total Baryon Fraction

• Baryon fraction flat with massTrade-off between stellar and ICM

baryons.

Star formation more efficient in lower mass systems


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


What do our results imply for the origin of the intracluster light?


Counting Baryons


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


• 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?



• 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

Does intracluster light lie on the fundamental plane?

How can extreme systems shed light on galaxy structure?


Counting Baryons

The Structure of GalaxiesEvolution of the Cluster

Galaxy Populations

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?

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)

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


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


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

QuickTime™ and aTIFF (LZW) decompressor


van den Bosch et al. (2007)


The Fundamental Manifold

rms = 0.099 (Not much worse than individual FPs.)

Fundamental Plane Fundamental Manifold

dE E

B

CG

CSph


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) 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.

•Large scatter in projection

• Only 24% scatter about second order fit in log V, log Ie

• 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)

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)


Counting Baryons Chemical Enrichment of the ICM

The Structure of Galaxies


Summary and Conclusions

Documents

The Distribution of Baryons in Galaxy Clusters and Groups