Metallicity and X-ray luminosity variations in NGC 922

TL;DR

This study investigates metallicity variations in NGC 922, revealing a correlation between metallicity and X-ray luminosity driven by young star-forming regions, aligning with models of X-ray binary populations.

Contribution

It provides the first detailed analysis of metallicity differences within NGC 922 and links these to X-ray luminosity variations, supporting existing models of X-ray binary behavior.

Findings

Metallicity varies from solar to sub-solar in different regions.

An anti-correlation exists between X-ray luminosity and metallicity.

Young star-clusters indicate recent star formation.

Abstract

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.