The NGC 4839 group falling into the Coma cluster observed by XMM-Newton ^*,**

¹ CEA/DSM/DAPNIA Saclay, Service d'Astrophysique, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette, France
² CEA/DSM/DAPNIA Saclay, SEI, 91191 Gif-sur-Yvette, France
³ IAS-CNRS, Universié Paris Sud, Bât. 121, 91405 Orsay Cedex, France
⁴ ESTEC, European Space & Technology Centre, Keplerlaan 1, Postbus 1, 2200 AG Noordwijk, The Netherlands
⁵ Max-Planck Institut für extraterrestrische Physik, Giessenbachstr., 85740 Garching, Germany
⁶ NIS-2, MS D436, Los Alamos National Laboratory, Los Alamos, NM 87454, USA
⁷ Dept. of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
⁸ IFC/CNR, Via Bassini 15, 20133 Milano, Italy
⁹ University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Nr. Dorking, Surrey, RH5 6NT, UK

Corresponding author: D. M. Neumann, ddon@cea.fr

Received: 2 October 2000
Accepted: 17 October 2000

Abstract

We present here the first analysis of the XMM-Newton EPIC-MOS data of the galaxy group around NGC 4839, which lies at a projected distance to the Coma cluster center of 1.6 Mpc. In our analysis, which includes imaging, spectro-imaging and spectroscopy we find compelling evidence for the sub group being on its first infall onto the Coma cluster. The complex temperature structure around NGC 4839 is consistent with simulations of galaxies falling into a cluster environment. We see indications of a bow shock and of ram pressure stripping around NGC 4839. Furthermore our data reveal a displacement between NGC 4839 and the center of the hot gas in the group of about 300 kpc. With a simple approximation we can explain this displacement by the pressure force originating from the infall, which acts much stronger on the group gas than on the galaxies.