  We reanalyze the ROSAT PSPC X-ray spectro-photometric observations of HCG 16.
Its X-ray morphology resembles its morphology at 20 cm, seen by the NVSS. We
detect diffuse emission in 8 regions filling half of the 200/h50 kpc (8.7")
radius circle around the optical center of the group: one encompassing galaxies
a&b, two surrounding galaxies c&d, a clumpy region roughly 140/h50 kpc from the
group galaxies, which may be gas ejected from one of the galaxies, plus regions
associated with background galaxies, radio-sources or groups, and foreground
stars. Excluding the background / foreground sources, we get L_X^bol = 2.3
10^41 / h50^2 erg/s, i.e. half the luminosity found by Ponman et al. The
diffuse emission is cool (T < 0.55 keV [90% confidence] with a best fit T =
0.27 keV). The correction for photoelectric absorption in L_X^bol is a factor
3.5 and varies rapidly with temperature. The clumpy distribution of hot diffuse
gas in HCG 16 is illustrated by the low mean X-ray surface brightness and hot
gas density of the regions of undetected emission within 8' (at most 1/4 and
1/6 of those of the detected gas, assuming both have same temperature,
metallicity and clumpiness). The irregular X-ray morphology of the diffuse
emission rules out a (nearly) virialized nature for HCG 16, unless
intergalactic gas had sufficiently high specific entropy to be unable to
collapse with the group. Most of the diffuse gas originates from galaxies,
either through tidal stripping or through galactic winds driven by supernova
remnants. Our results show the need for a careful 2D spatial analysis and
multi-wavelength study of the diffuse X-ray emission from groups, suggesting
that other compact groups could be significantly contaminated by superimposed
X-ray sources.(abridged)

Astrophysics