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

Abstract

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 $L_X = 3.03_{-0.04}^{+0.02}\times 10^{43}$ 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 LX = 1.13 ± 0.02 × 1043 erg s−1 in the 0.4–7.0 keV energy band. The average temperature and elemental abundance of A2151C(B) are 2.01 ± 0.05 keV and 0.43 ± 0.05 Z⊙, respectively, while these values are 1.17 ± 0.04 keV and 0.13 ± 0.02 Z⊙ for A2151C(F). Low temperature (1.55 ± 0.07 keV) and a short cooling time (∼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 a merger between the two subclumps.