AGN in Clusters of Galaxies

Paul MartiniThe Ohio State University

J.S. Mulchaey, D.D. Kelson (OCIW)E. Kim (CfA), A. Athey (OCIW)

Why Survey Clusters for AGN?

1. Different environment to probe AGN fueling (mergers, interactions, role of ISM)

2. Catalysts for galaxy evolution (ram pressure stripping, starvation, etc.)

3. Feedback of AGN on galaxy ISM and cluster ICM

4. Source of systematic error for X-ray (and SZ) cluster cosmology surveys

5. Large population of optically-dull AGN, much higher surface density than blank fields

Images from Sun et al. (2005); McNamara et al. (2006); Martini et al. (2002)

Why is this a MISST?

AGN Identification

35 (of 40) X-ray sources are AGN (10x or more X-ray luminous than either LMXBs or hot, gaseous halos)All but 4/35 (filled circles) are optically dullThe most luminous contribute ~10% of the cluster LX

We have identified 35 AGN in 8 clusters

LMXB relation from Kim & Fabbiano

(2004)

Hot Gas relation from O’Sullivan et al. (2003)

AGN DistributionRadial Distribution

Cumulative AGN and inactive galaxy distributions for all 8 clusters vs. R/r200

Kinematic DistributionDistributions vs. |v-vc|/

Substructure DistributionDistribution vs. where 2 = (11/2) [local - )2 + (local - )2](Dressler & Shectman 1988)

AGN and inactive galaxies have identical

distributions

AGN Fraction in Clusters

Cluster AGN Fraction: The fraction of galaxies brighter than MR = -20 mag with LX>1041 erg/s AGN

fA ~ 5% averaged over 8 clusters

Galaxy population brighter than MR<-20 mag is the main uncertainty

AC114 (z=0.31)

MR = -20

Martini et al. (2006b)

Dependence on Cluster Properties

There is good evidence for cluster to cluster variation

There are at best ‘intriguing trends’ between AGN fraction and various cluster propertiesMartini et al. (2006b)

Summary

• Cluster AGN fraction is unexpectedly high: fA ~ 5%• Most cluster AGN are optically

dull• Cluster AGN trace the cluster

galaxy population (to ~0.5 r200)• The AGN fraction varies from

cluster to cluster

Wish List for Future Cluster Surveys

• A larger sample to determine if substructure or velocity dispersion influences the AGN fraction in clusters

• A high-redshift sample (z>0.5) to determine if there is evolution

• Quantification of the impact on cluster cosmology studies

• A comparable field AGN fraction

(The ANEWs of this MISST)