Metallicity and X-ray luminosity variations in NGC922

We present a systematic study of the metallicity variations within the collisional ring galaxy NGC922 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 ([12 + log(O/H)] similar to 8.2). We detect He I emission in all the studied regions of the bulge and the ring, indicating ionization from massive stars associated with recent (<10 Myr) star formation, in agreement with the presence of very young star clusters. We find an anticorrelation between the X-ray luminosity and metallicity of the sub-galactic regions of NGC922. The different regions have similar stellar population ages, leaving metallicity as the main driver of the anticorrelation. The dependence of the X-ray emission of the different regions in NGC922 on metallicity is in agreement with similar studies of the integrated X-ray output of galaxies and predictions from X-ray binary population models.

Automated summary

This systematic study of the metallicity variations within the collisional ring galaxy NGC922 reveals a difference in metallicity between star-forming regions in the bulge and the ring. The study also shows an anticorrelation between X-ray luminosity and metallicity of the sub-galactic regions of NGC922.