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

Abstract

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.