The Hercules cluster in X-rays with $XMM$-$Newton$ and $Chandra$

Abstract

We present a detailed X-ray study of the central subcluster of the nearby ($z$ $\sim$0.0368) Hercules cluster (Abell 2151) identified as A2151C that shows a bimodal structure. A bright clump of hot gas with X-ray emission extending to radius $r$ $\sim$304 kpc and $L_X = 3.03_{-0.04}^{+0.02}\times10^{43}$ erg s$^{-1}$ in the 0.4$-$7.0 keV energy range is seen as a fairly regular subclump towards the west (A2151C(B)). An irregular, fainter and cooler subclump with radius $r$ $\sim$364 kpc is seen towards the east (A2151C(F)) and has $L_X=1.13\pm{0.02}\times10^{43}$ erg s$^{-1}$ in the 0.4$-$7.0 keV energy band. The average temperature and elemental abundance of A2151C(B) are $2.01\pm{0.05}$ keV and $0.43\pm{0.05}$ Z$_{\odot}$ respectively, while these values are $1.17\pm{0.04}$ keV and $0.13\pm{0.02}$ Z$_{\odot}$ for A2151C(F). Low temperature (${1.55}\pm{0.07}$ keV) and a short cooling time ($\sim$0.81 Gyr) within the central 15 arcsec region confirm the presence of a cool core in A2151C(B). We identify several compact groups of galaxies within A2151C(F). We find that A2151C(F) is a distinct galaxy group in the process of formation and likely not a ram-pressure stripped part of the eastern subcluster in Hercules (A2151E). X-ray emission from A2151C shows a region of overlap between A2151C(B) and A2151C(F) but without any enhancement of temperature or entropy in the two-dimensional (2D) projected thermodynamic maps that could have indicated an interaction due to merger between the two subclumps.