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A. Ptak (JHU), B. Mobasher (STScI), A. Hornschemeier (GSFC/LHEA), F. Bauer (Columbia University), C. Norman (JHU)
We present soft (0.5-2 keV) X-ray luminosity functions (XLFs) in the Great Observatories Origins Deep Survey (GOODS) fields, derived for early and late-type galaxies at z ~0.25 and 0.75. We estimate k-corrections for both the X-ray/optical and X-ray/NIR flux ratios, which facilitates the separation of AGN from the normal/starburst galaxies. The slopes of the early-type galaxy XLFs tend to be slightly flatter than the late-type galaxy XLFs, particularly in the normal/starburst galaxy subsample, although the effect is only marginally significant. We find that the slopes of the normal/starburst galaxy XLFs are significantly steeper at z>0.5 than at z<0.5. As expected, the ``full" sample XLF (all X-ray sources) is dominated by normal/starburst galaxies at the low-luminosity end and by AGN at the high-luminosity end (LX > 1041-42 ergs s-1). We find that the early-type galaxy XLFs are sampling a similar population as in a separate GOODS z=0.25 J-band luminosity function study. This provides additional broad evidence for the correlation between the X-ray emission of early-type galaxies and stellar mass, however the different luminosity function shapes (lognormal for the X-ray; Schechter for the J-band) is probably due to the J-band luminosity more directly tracking the stellar mass than the X-ray emission. The late-type XLFs derived from the normal/starburst sample agree well with rescaled local FIR luminosity functions assuming (1+z)3 luminosity evolution, at both high and low redshifts. This confirms that the X-ray emission from these galaxies is closely tracking star formation-related processes.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.