ChAInGeS: The Chandra Arp Interacting Galaxies Survey

TL;DR

This study analyzes ultra-luminous X-ray sources in peculiar galaxies, finding they are often linked to star formation and are more common in interacting galaxies, with some variations related to infrared luminosity and nuclear activity.

Contribution

It provides the first statistical analysis of ULXs in the Arp Atlas of Peculiar Galaxies, revealing their correlation with star formation and galaxy interactions.

Findings

ULX numbers are enhanced in strongly interacting galaxies.

ULXs are often located in regions with young stellar populations.

Infrared-luminous galaxies show a ULX deficiency, possibly due to obscuration or AGN activity.

Abstract

We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L(X) >= 10^39 erg/s) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of ~2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, AGNs may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using GALEX UV and SDSS optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of ~2 - 5 in the fraction of galactic nuclei that are X-ray bright compared to more normal spirals.