AAS 207th Meeting, 8-12 January 2006
Session 178 UV and X-ray Observations of Normal Galaxies
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[178.05] Constraining the Redshift Evolution of Off-Nuclear X-ray Sources using the Chandra Deep Fields.

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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