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B. D. Lehmer, W. N. Brandt (PSU), A. E. Hornschemeier (Goddard), D. M. Alexander (IoA), F. E. Bauer (Columbia), A. M. Koekemoer (STScI), D. P. Schneider, A. T. Steffen (PSU)
We analyze a population of intermediate-redshift (z = 0.05-0.3) off-nuclear X-ray sources located within the optical extent of optically-bright galaxies in the Great Observatories Origins Deep Survey (GOODS) and Galaxy Evolution from Morphology and SEDs (GEMS) fields. A total of 19 off-nuclear sources are classified using deep Chandra exposures from the Chandra Deep Field-North, Chandra Deep Field-South, and Extended Chandra Deep Field-South; ten of these sources are newly identified. These sources have average X-ray spectral shapes and optical environments similar to those of ultraluminous X-ray sources (ULXs) in the local univese. This sample improves the available source statistics for intermediate-redshift off-nuclear sources with 0.5-2.0 keV luminosities L0.5-2.0 keV > 1039.5 erg s-1, and places significant new constraints on the redshift evolution of the off-nuclear source frequency in field galaxies. We find that the fractions of intermediate-redshift field galaxies containing an off-nuclear source are elevated by a factor of two with respect to those observed for ULXs in the local universe for 0.5-2.0 keV luminosities in the range of 1039-40.5 erg s-1; the rise in these fractions is consistent with that expected from the observed increase in global star-formation density with redshift.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.