On Ultraluminous X-ray Source Correlations with Star-Forming Regions
Abstract
Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u-g, g-r and r-i colors are used to determine whether Ultraluminous X-ray sources (ULXs) are predominantly associated with star-forming regions of their host galaxies. An empirical selection criterion is derived from colors of HII regions in M81 and M101 that differentiates between the young, blue stellar component and the old disk and bulge population. This criterion is applied to a sample of and verified through an application of Fisher's linear discriminant analysis. It is found that 60% (49%) of ULXs in optically-bright environments are within regions blueward of their host galaxy's HII regions compared to only 27% (0%) of a control sample according to the empirical (Fisher) criterion. This is an excess of 3-sigma above the 32% (27%) expected if the ULXs were randomly distributed within their galactic hosts. This indicates a ULX preference for young, approximately <10 Myr, OB associations. We show that the environments surrounding the brightest ULXs are consistent with the onset of an accretion phase as the donor star ascends the giant branch if the donor is a <20 solar-mass star.
- Publication:
-
Chandra's First Decade of Discovery
- Pub Date:
- September 2009
- Bibcode:
- 2009cfdd.confE.201S
- Keywords:
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- Compact Objects