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.
Highlights
The Hickson-16 galaxy group comprises seven galaxies with a mean recession velocity (Ribeiro et al 1996) of 3959 ± 66 km s−1 and a velocity dispersion of 86 ± 55 km s−1, centered on the position α = 02◦09 33, δ = −10◦09 46.7 (J2000)
This paper presents the XMM -Newton first-light observations of the Hickson-16 compact group of galaxies
Since EPIC resolves the optical disks of the galaxies, the spectra were prepared from photons falling within a region of interest based on the X-ray image
Summary
The Hickson-16 galaxy group (or HCG-16) comprises seven galaxies with a mean recession velocity (Ribeiro et al 1996) of 3959 ± 66 km s−1 and a velocity dispersion of 86 ± 55 km s−1, centered on the position α = 02◦09 33 , δ = −10◦09 46.7 (J2000). The four central members of the group, originally identified by Hickson (Hickson 1982), all fall within the 30 field of view of EPIC, they all show evidence for mergers and a strong ionising continuum; they have well resolved optical nuclei (Mendes de Oliveira et al 1998). L. Turner et al.: XMM -Newton first-light observations of the Hickson galaxy group 16
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