X-ray Point Sources and Radio Galaxies in Clusters: Source of Distributed Heating of the ICM?

TL;DR

This study investigates the properties of X-ray point sources and radio galaxies in galaxy clusters, suggesting they are low-luminosity BL Lac objects and FR 1s that could contribute to heating the intracluster medium.

Contribution

It provides evidence that cluster X-ray sources are likely low-luminosity BL Lacs and FR 1s, proposing their role in distributed heating of the ICM.

Findings

75% of X-ray point sources are within 500 kpc of cluster centers

Cluster XPSs are hosted by passive red galaxies with AGN-like X-ray spectra

Relativistic jets from these sources may inject energy into the ICM

Abstract

In our ongoing multi-wavelength study of cluster AGN, we find ~75% of the spectroscopically identified cluster X-ray point sources (XPS) with L(0.3-8.0keV)>10^{42} erg s^{-1} and cluster radio galaxies with P(1.4 GHz) > 3x10^{23} W Hz^{-1} in 11 moderate redshift clusters (0.2<z<0.4) are located within 500 kpc from the cluster center. In addition, these sources are much more centrally concentrated than luminous cluster red sequence (CRS) galaxies. With the exception of one luminous X-ray source, we find that cluster XPSs are hosted by passive red sequence galaxies, have X-ray colors consistent with an AGN power-law spectrum, and have little intrinsic obscuring columns in the X-ray (in agreement with previous studies). Our cluster radio sources have properties similar to FR1s, but are not detected in X-ray probably because their predicted X-ray emission falls below our sensitivity limits. Based on the observational properties of our XPS population, we suggest that the cluster XPSs are low-luminosity BL Lac objects, and thus are beamed low-power FR 1s. Extrapolating the X-ray luminosity function of BL Lacs and the Radio luminosity function of FR 1s down to fainter radio and X-ray limits, we estimate that a large fraction, perhaps all CRSs with L>L* possess relativistic jets which can inject energy into the ICM, potentially solving the uniform heating problem in the central region of clusters.