XMM-Newton first-light observations of the Hickson galaxy group 16
Arnaud, M.; Clavel, J.; Priedhorsky, W.; Boer, M.; Dos Santos, S.; Molendi, S.; Ghizzardi, S.; La Palombara, N.; Jansen, F.; Vigroux, L.; Reeves, J. N.; Ward, M.; Hochedez, J. F.; Ferrando, P.; Ponman, T. J.; Trümper, J.; Mason, K. O.; Bennie, P. J.; Kendziorra, E.; Vercellone, S.; Trifoglio, M.; Turner, M. J. L.; Strüder, L.; Lortholary, M.; Holland, A. D.; Sembay, S.; Short, A.; Rothenflug, R.; Barbera, M.; Griffiths, R. G.; Reppin, C.; Villa, G.; Cordova, F.; Pigot, C.; Schmitt, D.; Briel, U.; Butler, I.; Dhez, P.; Goodall, C. V.; Lagostina, A.; Laine, R.; Salvetat, P.; Sauvageot, J.
United Kingdom, France, Italy, Germany, Spain, United States, Netherlands
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.