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 ∼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 ∼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 ∼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 merger between the two subclumps.

Unveiling the internal structure of Hercules supercluster

“…The first encounter between them will happen relatively soon, in 0.4 Gyr. Also, the conjecture of Tiwari & Singh (2021) that A2151C-F is a cluster in formation is supported by our analysis. In this work, we have confirmed quantitatively that A2151S is part of Hercules cluster, being gravitationally bound with it.…”

“…At last, we have compared our mass estimations with those available in the literature. The mass estimated by Tiwari & Singh (2021) for A2151C-B is 1.3 ± 0.8 × 10 14 M and for A2151C-F is 0.42 ± 0.30 × 10 14 M . Both are consistent with our results within their error bars.…”

“…Due to the model's inability to discern between the pre-and post-merging states, we will describe both scenarios for the bounded pairs. The only relatively unquestionable fact is the pre-merger state between the central substructures in the sense that the cool core of A2151C-B is still preserved (Laganá et al 2019;Tiwari & Singh 2021). The encounter will be happening in 0.38 +0.12 −0.20 Gyr with a velocity of 1147 +169 −139 km s −1 at a moderated distance of the plane of the sky (46 +22 −19 degrees).…”

The complex intracluster medium of Abell 1569 and its interaction with central radio galaxies

“…We have used a single Chandra ACIS-I X-ray observation of A1569 in this work. The observational data were obtained from the HEASARC 2 archive and have the following specifications: Observation ID: 6100 Date of observation: 2005 April 07 Pointing RA (J2000): 12 ℎ 36 𝑚 36 𝑠 .59 Pointing Dec (J2000): +16°36 50 .00 Data mode: Very Faint Useful exposure time: 41.75 ks X-ray data were reduced, screened and analysed using Chandra Interactive Analysis of Observations (CIAO) software version 4.12 and Calibration Database (CALDB) version 4.9.1 as described in detail in §2.2 of Tiwari & Singh (2021). The description therein also includes procedures used for point source subtraction, image generation, background subtraction and spectral extraction.…”

“…The extracted spectra were simultaneously fitted with the RASS diffuse background spectrum using the XSPEC model: constant*(apec+(apec+apec+pegpwrlw)*tbabs + apec*tbabs). The individual model component definitions are the same as described in §3.2 of Tiwari & Singh (2021). We fixed the total hydrogen column density (neutral+molecular), 𝑁 𝐻 , along the line of sight (LOS) to the subclusters, to values provided by the UK Swift Science Data Centre 5 (Willingale et al 2013).…”