X-ray Properties of Young Early Type Galaxies: I. X-ray Luminosity Function of LMXBs

TL;DR

This study compares the X-ray luminosity functions of LMXBs in young versus old elliptical galaxies, revealing significant differences likely linked to recent mergers and star formation activities.

Contribution

It provides the first detailed comparison showing that young elliptical galaxies have a distinct XLF shape and higher fraction of luminous LMXBs compared to old ellipticals.

Findings

Young ellipticals lack the high luminosity break seen in old ellipticals.

Young ellipticals host more luminous LMXBs than old ellipticals.

XLF of young ellipticals is intermediate between old ellipticals and star-forming galaxies.

Abstract

We have compared the combined X-ray luminosity function (XLF) of 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 x 1038 erg s-1 found in the old elliptical galaxy XLF. The 'young' and 'old' XLFs differ with a 3{\sigma} 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 x 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.