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[15.13] The Ultra-Luminous X-ray Sources and their Host Galaxies

D. A. Swartz, K. K. Ghosh, A. F. Tennant, K. Wu (NASA MSFC)

We present X-ray spectral, spatial, and variability distributions for 154 discrete non-nuclear Ultra-Luminous X-ray (ULX) sources identified in 82 galaxy observations obtained from the Chandra/ACIS archive. Correlations with host galaxy properties confirm the number and total X-ray luminosity of the ULXs are associated withrecent star formation and with galaxy merging and interactions. The large number of ULXs in star-forming galaxies suggest they originate in a young but short-lived population such as the high-mass X-ray binaries with a smaller contribution (based on spectral slope) from recent supernovae. The number of ULXs in elliptical galaxies scales with host galaxy mass and can be explained most simply as the high-luminosity end of the low-mass X-ray binary population. Comparison of the cumulative X-ray luminosity functions of the ULXs to Chandra Deep Field results suggests ~25 background objects including 14 the sample of spiral galaxies and 44 galaxies implying the elliptical galaxy ULX population is severely compromised by background active galactic nuclei.

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.