X-ray properties of young early-type galaxies. I. X-ray luminosity function of low-mass X-ray binaries

Abstract

We have compared the combined X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) detected in Chandra observations of young, post-merger elliptical galaxies with that of typical old elliptical galaxies.We find that the XLF of the "young" sample does not present the prominent high-luminosity break at LX > 5 × 1038 erg s -1 found in the old elliptical galaxy XLF. The "young" and "old" XLFs differ with a 3s statistical significance (with a probability less than 0.2% that they derive from the same underlying parent distribution). Young elliptical galaxies host a larger fraction of luminous LMXBs (LX > 5 × 1038 erg s-1) than old elliptical galaxies and the XLF of the young galaxy sample is intermediate between that of typical old elliptical galaxies and that of star-forming galaxies. This observational evidence may be related to the last major/minor mergers and the associated star formation. © 2010. The American Astronomical Society. All rights reserved.