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

This paper presents the XMM-Newton first-light observations of the Hickson- 16 compact group of galaxies. Groups are possibly the oldest large-scale st ructures in the Universe, pre-dating clusters of galaxies, and are highly e volved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) i s exceptional in the having the highest concentration of starburst or AGN a ctivity in the nearby Universe. So it is a veritable laboratory for the stu dy of the relationship between galaxy interactions and nuclear activity. Pr evious optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was uncle ar. Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocall y reveals a heavily obscured AGN and a separately identified thermal (starb urst) plasma, in NGC 835, NGC 833, & NGC 839. NGC 838 shows only starburst thermal emission. Starbursts and AGN can evidently coexist in members of th is highly evolved system of merged and merging galaxies, implying a high pr obability for the formation of AGN as well as starbursts in post-merger gal axies.