The stripping of a galaxy group diving into the massive cluster A2142

D. Eckert, S. Molendi, M. Owers, M. Gaspari, T. Venturi, L. Rudnick, S. Ettori, S. Paltani, F. Gastaldello, M. Rossetti

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Abstract

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.

Original languageEnglish (US)
Article numberA119
JournalAstronomy and Astrophysics
Volume570
DOIs
StatePublished - Oct 1 2014

Bibliographical note

Funding Information:
Eckert D. 1 2 Molendi S. 2 Owers M. 3 Gaspari M. 4 5 Venturi T. 6 Rudnick L. 7 Ettori S. 5 8 Paltani S. 1 Gastaldello F. 2 9 Rossetti M. 10 2 1 Department of Astronomy, University of Geneva , Ch. d’Ecogia 16 , 1290 Versoix , Switzerland 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 e-mail: Dominique.Eckert@unige.ch 30 10 2014 30 10 2014 10 2014 570 aa/2014/10 A119 23 5 2014 5 8 2014 © ESO, 2014 2014 ESO 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 10 13 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. galaxies: groups: general galaxies: clusters: general galaxies: clusters: intracluster medium X-rays: galaxies: clusters large-scale structure of Universe idline A&A 570, A119 (2014) cover_date October 2014 first_month 10 last_month 10 first_year 2014 last_year 2014 Based on observations obtained with XMM-Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. We thank the staff of the GMRT that made the radio observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. D.E. thanks Elke Roediger, Jean-Paul Kneib and HuanYuan Shan for useful discussions. Partial support for L.R. comes from US NSF Grant AST-1211595 to the University of Minnesota.

Publisher Copyright:
© ESO, 2014.

Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.

Keywords

  • Galaxies: clusters: general
  • Galaxies: clusters: intracluster medium
  • Galaxies: groups: general
  • Large-scale structure of Universe
  • X-rays: galaxies: clusters

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