Deep Chandra observations of the stripped galaxy group falling into Abell 2142

¹ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
e-mail: Dominique.Eckert@unige.ch
² INAF–IASF-Milano, Via E. Bassini 15, 20133 Milano, Italy
³ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544-1001 USA
⁴ Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
⁵ Department of Physics and Astronomy, Macquarie University, NSW, 2109, Australia
⁶ E.A. Milne Centre for Astrophysics, University of Hull, Hull, HU6 7RX, UK
⁷ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁸ INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁹ INAF–Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
¹⁰ Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA

Received: 3 February 2017
Accepted: 14 May 2017

Abstract

In the local Universe, the growth of massive galaxy clusters mainly operates through the continuous accretion of group-scale systems. The infalling group in Abell 2142 is the poster child of such an accreting group, and as such, it is an ideal target to study the astrophysical processes induced by structure formation. We present the results of a deep (200 ks) observation of this structure with Chandra that highlights the complexity of this system in exquisite detail. In the core of the group, the spatial resolution of Chandra reveals a leading edge and complex AGN-induced activity. The morphology of the stripped gas tail appears straight in the innermost 250 kpc, suggesting that magnetic draping efficiently shields the gas from its surroundings. However, beyond ~300 kpc from the core, the tail flares and the morphology becomes strongly irregular, which could be explained by a breaking of the drape, for example, caused by turbulent motions. The power spectrum of surface-brightness fluctuations is relatively flat (P_2D ∝ k^-2.3), which indicates that thermal conduction is strongly inhibited even beyond the region where magnetic draping is effective. The amplitude of density fluctuations in the tail is consistent with a mild level of turbulence with a Mach number M_3D ~ 0.1 − 0.25. Overall, our results show that the processes leading to the thermalization and mixing of the infalling gas are slow and relatively inefficient.