The X-Ray Luminosity Function of Ultra Luminous X-Ray Sources in Collisional Ring Galaxies

TL;DR

This study investigates the X-ray luminosity function of ULXs in collisional ring galaxies, revealing similarities to other galaxy types but with a higher fraction of luminous sources, highlighting the impact of galaxy collisions on X-ray source populations.

Contribution

It provides the first detailed analysis of ULX populations in collisional ring galaxies and compares their XLF to other galaxy types, noting a higher fraction of high-luminosity ULXs.

Findings

Total ULX count is 63, with 50 exceeding 10^39 erg s^-1.

The XLF shape is similar to other galaxies but with more high-luminosity sources.

ULX numbers per star formation rate are at the upper end of normal galaxy distributions.

Abstract

Ring galaxies are fascinating laboratories: a catastrophic impact between two galaxies (one not much smaller than the other) has produced fireworks especially in the larger one, when hit roughly perpendicularly to the plane. We analyze the point sources, produced by the starburst episode following the impact, in the rings of seven galaxies and determine their X-ray luminosity function (XLF). In total we detect 63 sources, of which 50 have luminosity L$_X \geq 10^{39}$ erg s$^{-1}$, classifying them as ultra luminous X-ray sources (ULXs). We find that the total XLF is not significantly different from XLFs derived for other kinds of galaxies, with a tendency of having a larger fraction of high X-ray luminosity objects. Both the total number of ULXs and the number of ULXs per unit star formation rate are found in the upper envelope of the more normal galaxies distribution. Further analysis would be needed to address the issue of the nature of the compact component in the binary system.