Metallicity and X-ray luminosity variations in NGC 922
  We present a systematic study of the metallicity variations within the
collisional ring galaxy NGC 922 based on long-slit optical spectroscopic
observations. We find a metallicity difference between star-forming regions in
the bulge and the ring, with metallicities ranging from almost solar to
significantly sub-solar ($\rm{[12+\log(O/H)]\sim 8.2}$). We detect $\rm He\,_I$
emission in the bulge and the ring star-forming regions indicating ionization
from massive stars associated with recent ($<10$ Myr) star-formation, in
agreement with the presence of very young star-clusters in all studied regions.
We find an anti-correlation between the X-ray luminosity and metallicity of the
sub-galactic regions of NGC 922. The different regions have similar stellar
population ages leaving metallicity as the main driver of the anti-correlation.
The dependence of the X-ray emission of the different regions in NGC 922 on
metallicity is in agreement with similar studies of the integrated X-ray output
of galaxies and predictions from X-ray binary population models.
