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The Properties and Redshift Evolution of Intermediate-Luminosity Off-Nuclear X-Ray Sources in the Chandra Deep Fields

Lehmer, B.D.; Brandt, W.N.; Hornschemeier, A.E.; Alexander, D.M.; Bauer, F.E.; Koekemoer, A.M.; Schneider, D.P.; Steffen, A.T.


B.D. Lehmer

W.N. Brandt

A.E. Hornschemeier

F.E. Bauer

A.M. Koekemoer

D.P. Schneider

A.T. Steffen


We analyze a population of intermediate-redshift (z~0.05-0.3) off-nuclear X-ray sources located within optically bright galaxies in the Great Observatories Origins Deep Survey and Galaxy Evolution from Morphology and SEDs fields. A total of 24 off-nuclear source candidates are classified using deep Chandra X-Ray Observatory exposures from the Chandra Deep Field-North, Chandra Deep Field-South, and Extended Chandra Deep Field-South 15 of these are newly identified. These sources have average X-ray spectral shapes and optical environments similar to those observed for off-nuclear intermediate-luminosity (LX>=1039 ergs s-1 in the 0.5-2.0 keV band) X-ray objects (IXOs; sometimes referred to as ultraluminous X-ray sources) in the local universe. This sample improves the available source statistics for intermediate-redshift off-nuclear sources with LX>~1039.5 ergs s-1, and it places significant new constraints on the redshift evolution of the off-nuclear source frequency in field galaxies. The fraction of intermediate-redshift field galaxies containing an off-nuclear source with LX>~1039 ergs s-1 is suggestively elevated (~80% confidence level) with respect to that observed for IXOs in the local universe; we calculate this elevation to be a factor of ~1.9+1.4-1.3. A rise in this fraction is plausibly expected as a consequence of the observed increase in global star formation density with redshift, and our results are consistent with the expected magnitude of the rise in this fraction.


Lehmer, B., Brandt, W., Hornschemeier, A., Alexander, D., Bauer, F., Koekemoer, A., …Steffen, A. (2007). The Properties and Redshift Evolution of Intermediate-Luminosity Off-Nuclear X-Ray Sources in the Chandra Deep Fields. Astronomical Journal, 131(5), 2394-2405.

Journal Article Type Article
Acceptance Date Jan 30, 2006
Online Publication Date Oct 30, 2007
Publication Date Oct 30, 2007
Deposit Date Jan 21, 2008
Journal Astronomical Journal
Print ISSN 0004-6256
Electronic ISSN 1538-3881
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 131
Issue 5
Pages 2394-2405
Keywords Cosmology, Observations, Diffuse Radiation, Surveys, X-rays.
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