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 Cosmology and Galaxy Structure from Extreme Galaxies

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 BaryonsChemical 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 ( s) in Gunn I –30 Abell/APM clusters ( km/s) at z= 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 ≈ h 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 (r 1/4 ) Abell 2571: An Example

Sharp breaks in ellipticity and PA Single Sersic (r 1/n ) Abell 2571: An Example deV – Sersic Avg  2 = 3650 (1 dof)

Abell 2571: An Example 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? Intracluster Light & Brightest Cluster Galaxies 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 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 Gas Stars Ettori et al. 2006

Observational Constraints What does one see: –Increasing gas fraction (f g )with cluster mass –Increasing total baryon fraction (f g + f * ) with M 200 –Limited information about radial dependence of total baryon fraction Vikhlinin et al 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 r 200 r 500 r ’

Tools for the Census... Prerequisites –Cluster Radius X-ray data generally lacking for sample Calibrate  -r 500 and  -r 200 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  -M 500 relation using subset of Vikhlinin et al. sample

Tools for the Census...  -M 500 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? Gonzalez et al. 2007

Total Stellar Mass Luminosity  Stellar mass –Using SAURON results –Luminosity-weighted M/L for L>0.25 L * – =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 )= log(M 500 ) Gonzalez et al ) Gonzalez 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 )= log(M 500 ) log(f g,500 )= log(M 500 ) Gonzalez et al. (2007)

Total Baryon Fraction 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 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 r 500 (~10%) Missing Baryons Must be independent of M 500. No compelling evidence currently. WMAP Incorrect See McCarthy et al Gonzalez et al. (2007)

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

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) M BCG+ICL L ICL /(L BCG +L ICL ) Conroy 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? 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. Selection Bias? Purcell et al. 2007

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 Galaxies Evolution of the Cluster Galaxy Populations

The Fundamental Plane Basic Expectation: Virial Equilibrium  2 +GM/r e = 0 →  2 ~ (M/L)(I e r e 2 )/r e log r e = 2 log  – log I e – log (M/L) + C General Observation for Ellipticals –Very tight relation (Fundamental Plane, rms=0.085) –Tilted relative to virial expectation log r e = 1.21 log  – 0.77 log I e + 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 +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 r e = 2 log  – log I e – log (M/L) + C Zaritsky, Gonzalez, & Zabludoff (2006a)

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) M/L variations Too large for stellar populations Not described by power law Zaritsky, Gonzalez, & Zabludoff (2006a)

What is driving change in “A”? Assume log M/L ~ (  log  –  ) 2 Not unique, but sufficient Dwarf spheroids not included in fit log r e = -  2 log 2  +2(1+  )log  +B log I e +C van den Bosch et al. (2007) Zaritsky, Gonzalez, & Zabludoff (2006a)

The Fundamental Manifold rms = (Not much worse than individual FPs.) Fundamental Plane Fundamental Manifold dE E BCG CSph Zaritsky, Gonzalez, & Zabludoff (2006a)

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 V 2 = (1/2) v c 2 +  2, for an isothermal sphere the virial eq. is: AV 2 =B GM/r which yields: log r e = log V 2 - log I e - 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 I e

Good agreement between dynamical and best-fit M/L log r e = log V 2 - log I e - 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  M/L is main driver for observed variation  Other factors secondary (environment, AGN, accretion history,…) Jorgensen et al. (1996) Springob et al. (2007)

Intracluster Light & Brightest Cluster Galaxies Counting BaryonsChemical Enrichment of the ICM The Structure of Galaxies Evolution of the Cluster Galaxy Populations Summary and Conclusions