Journal Article

A joint <i>Chandra</i> and <i>XMM–Newton</i> view of Abell 3158: a massive off-centre cool gas clump as a robust diagnostic of a merger stage

Yu Wang, Haiguang Xu, Liyi Gu, Junhua Gu, Zhenzhen Qin, Jingying Wang, Zhongli Zhang and Xiang-Ping Wu

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 4, pages 1909-1918
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI:
A joint Chandra and XMM–Newton view of Abell 3158: a massive off-centre cool gas clump as a robust diagnostic of a merger stage

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In previous works, the nearby galaxy cluster Abell 3158 was reported to possess a relatively regular, relaxed morphology in the X-ray band. By analysing the Chandra and XMM–Newton archived data of Abell 3158, we have identified a bow-edge-shaped discontinuity in the X-ray surface brightness distribution about 120 h−171 kpc west of the X-ray peak. This feature is found to be associated with a massive, off-centre cool gas clump, and actually forms the west boundary of the cool clump. By calculating the thermal gas pressures in the cool clump and in the free-stream region, we determine that the cool gas clump is moving at a subsonic velocity of 700+140−340 km s−1 (M= 0.6+0.1−0.3) towards west on the sky plane. We exclude the possibility that this cool clump was formed by local inhomogeneous radiative cooling in the intracluster medium, because of the effectiveness of the thermal conduction on the time-scale of ∼0.3 Gyr. As no evidence for central active galactic nucleus activity has been found in Abell 3158, and this cool clump bears many similarities to the off-centre cool gas clumps detected in other merging clusters in terms of their mass, size, location and thermal properties (e.g. lower temperature and higher abundance as compared with the environment), we speculate that the cool clump in Abell 3158 was caused by a merger event, and is the remnant of the original central cool-core of the main cluster or the infalling subcluster. This idea is supported not only by the study of the line-of-sight velocity distribution of the cluster member galaxies, but also by the study of the gas entropy–temperature correlation. This example shows that the appearance of such massive, off-centre cool gas clumps can be used to diagnose the dynamical state of a cluster, especially when prominent shocks and cold fronts are absent.

Keywords: galaxies: clusters: individual: Abell 3158; intergalactic medium; galaxies: kinematics and dynamics; X-rays: galaxies: clusters

Journal Article.  6727 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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