Volume 570, October 2014
|Number of page(s)||10|
|Section||Cosmology (including clusters of galaxies)|
|Published online||30 October 2014|
The stripping of a galaxy group diving into the massive cluster A2142
Department of Astronomy, University of Geneva,
Ch. d’Ecogia 16, 1290
2 INAF – IASF-Milano, via E. Bassini 15, 20133 Milano, Italy
3 Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
4 Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany
5 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6 INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
7 Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA
8 INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
9 Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697-4575, USA
10 Università degli studi di Milano, Dip. di Fisica, via Celoria 16, 20133 Milano, Italy
Received: 23 May 2014
Accepted: 5 August 2014
Structure formation in the current Universe operates through the accretion of group-scale systems onto massive clusters. The detection and study of such accreting systems is crucial to understand the build-up of the most massive virialized structures we see today. We report the discovery with XMM-Newton of an irregular X-ray substructure in the outskirts of the massive galaxy cluster Abell 2142. The tip of the X-ray emission coincides with a concentration of galaxies. The bulk of the X-ray emission of this substructure appears to be lagging behind the galaxies and extends over a projected scale of at least 800 kpc. The temperature of the gas in this region is 1.4 keV, which is a factor of ~4 lower than the surrounding medium and is typical of the virialized plasma of a galaxy group with a mass of a few 1013 M⊙. For this reason, we interpret this structure as a galaxy group in the process of being accreted onto the main dark-matter halo. The X-ray structure trailing behind the group is due to gas stripped from its original dark-matter halo as it moves through the intracluster medium (ICM). This is the longest X-ray trail reported to date. For an infall velocity of ~1200 km s-1 we estimate that the stripped gas has been surviving in the presence of the hot ICM for at least 600 Myr, which exceeds the Spitzer conduction timescale in the medium by a factor of ≳400. Such a strong suppression of conductivity is likely related to a tangled magnetic field with small coherence length and to plasma microinstabilities. The long survival time of the low-entropy intragroup medium suggests that the infalling material can eventually settle within the core of the main cluster.
Key words: galaxies: groups: general / galaxies: clusters: general / galaxies: clusters: intracluster medium / X-rays: galaxies: clusters / large-scale structure of Universe
© ESO, 2014
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