Discovery of galaxy clusters and a head-tail radio galaxy in the direction of globular cluster NGC 6752

Abstract

We report on the discovery of CXOU J191100-595621 and CXOU J191012-595619, two galaxy clusters serendipitously detected in the direction of globular cluster NGC 6752, based on archival Chandra observations with a total exposure time of ~344 ks. The deep Chandra X-ray data enabled us to measure the properties of both systems. We found a redshift of z = 0.239 ± 0.013 and z = 0.375 ± 0.016, a temperature of $kT=3.32^{+0.57}_{-0.46}$ keV and $kT=3.71^{+1.18}_{-0.86}$ keV, an iron abundance of $Z_{\rm Fe}=0.64^{+0.34}_{-0.29}Z_{\rm Fe\odot }$ and $Z_{\rm Fe}=1.29^{+0.97}_{-0.65}Z_{\rm Fe\odot }$ and a rest-frame full band (0.5-7 keV) luminosity of $L_{\rm X}=9.2^{+1.2}_{-1.1}\times 10^{43} {\rm \, erg\, s^{-1}}$ and $L_{\rm X}=9.9^{+2.7}_{-2.2}\times 10^{43} {\rm \, erg\, s^{-1}}$ for CXOU J191100-595621 and CXOU J191012-595619, respectively. The temperature profile of CXOU J191100-595621 is found to decrease with decreasing radius, indicating a cool core in this cluster. The hydrostatic equilibrium estimation suggests that the clusters are moderately weighted, with $M_{500}=(1.3\pm 0.4)\times 10^{14}\, \mathrm{M}_{\odot }$ and $M_{500}=(2.0\pm 1.5)\times 10^{14}\, \mathrm{M}_{\odot }$, respectively. We search for optical and radio counterparts of X-ray point sources in the clusters. Three active galactic nuclei are found, among which one is identified with a narrow-angle-tail radio galaxy, and one is found to be associated with the brightest central galaxy of CXOU J191100-595621.