The AGN content of the z=0.83 cluster MS1054-0321

TL;DR

This study uses Chandra X-ray observations to identify and analyze the active galactic nucleus (AGN) population in the galaxy cluster MS1054-0321 at redshift 0.83, revealing an excess of AGN compared to field expectations and insights into their spatial distribution.

Contribution

First X-ray survey of AGN in MS1054-0321, showing enhanced AGN activity and spatial distribution differences compared to local clusters.

Findings

Detected 47 X-ray sources, 2 confirmed cluster members.

Found ~2 sigma excess of AGN compared to field surveys.

AGN are predominantly located 1-2 Mpc from the cluster center.

Abstract

We present a survey of X-ray point sources in a 91 ksec Chandra ACIS-S observation of the z=0.83 cluster MS1054-0321. We detect 47 X-ray sources within the 8.3 arcmin by 8.3 arcmin field, of which two are immediately confirmed from pre-existing spectroscopy to be at the redshift of the cluster. At fluxes brighter than S_(0.5 - 8 keV) = 5 x 10^{-15} erg s^{-1} cm^{-2} we find a ~ 2 sigma excess compared to predictions from field surveys, consistent with an excess of approximately 6 AGN. If these sources are associated with the cluster, they too are AGN with luminosities of order L_(0.5 - 8 keV) ~ 10^{43} erg s^{-1}. Combined with the identification of 7 cluster AGN from deep radio observations (Best et al. 2002), these observations suggest significantly enhanced AGN activity in MS1054-03 compared to local galaxy clusters. Interestingly, the excess of X-ray detected AGN is found at radial distances of between 1 and 2 Mpc, suggesting they may be associated with infalling galaxies. The radio AGN are seen within the inner Mpc of the cluster and are largely undetected in the X-ray, suggesting they are either intrinsically less luminous and/or heavily obscured.