ChAInGeS: The Chandra Arp Interacting Galaxies Survey
  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.
