XMM-Newton first-light observations of the Hickson galaxy group 16

¹ X-ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
² School of Physics and Astronomy, University of Birmingham, B15 2TT, UK
³ CEA Saclay, 91191 Gif-sur-Yvette, France
⁴ Osservatorio Astronomico di Palermo, Palermo 90134, Italy
⁵ CESR Toulouse, BP 4346, 31028 Toulouse Cedex 4, France
⁶ Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, 85748 Garching, Germany
⁷ ESA-SOC, Vilspa, PO Box 50727, 28080, Madrid, Spain
⁸ LURE, Bât. 209 D, Université Paris Sud, 91405 Orsay, France
⁹ Office of Research, University of California, Santa Barbara, CA 93106, USA
¹⁰ IFC Milan, 20133 Milano, Italy
¹¹ Institut d'Astrophysique Spatiale, Bât. 121, Université Paris Sud, 91405 Orsay, France
¹² PS Estec, Postbus 299, 2200 AG Noordwijk, The Netherlands
¹³ IAAP Tuebingen, 72076, Germany
¹⁴ PX Estec, Postbus 299, 2200 AG Noordwijk, The Netherlands
¹⁵ MSSL Holmbury St Mary, Dorking RH5 6NT, UK
¹⁶ LANL, SST9, MS D436, Los Alamos, NM 87545, USA
¹⁷ ITESRE, 41010 Bologna, Italy

J. N. Reeves

Received: 13 October 2000
Accepted: 27 October 2000

Abstract

This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentration of starburst or AGN activity in the nearby Universe. So it is a veritable laboratory for the study of the relationship between galaxy interactions and nuclear activity. Previous optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was unclear. Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocally reveals a heavily obscured AGN and a separately identified thermal (starburst) plasma, in NGC 835, NGC 833, & NGC 839. NGC 838 shows only starburst thermal emission. Starbursts and AGN can evidently coexist in members of this highly evolved system of merged and merging galaxies, implying a high probability for the formation of AGN as well as starbursts in post-merger galaxies.