Dependence of the LMXB population on stellar age
  We investigate the dependence of the low-mass X-ray binary (LMXB) population
in early-type galaxies on stellar age, by selecting 20 massive nearby
early-type galaxies from the Chandra archive occupying a relatively narrow
range of masses and spanning a broad range of ages, from 1.6 Gyr to more than
10 Gyrs, with the median value of 6 Gyrs. With the ~ 2000 X-ray point sources
detected in total, we correlated the specific number of LMXBs in each galaxy
with its stellar age and globular cluster (GC) content. We found a correlation
between the LMXB population and stellar age: older galaxies tend to possess
about ~50% more LMXBs (per unit stellar mass) than the younger ones. The
interpretation of this dependence is complicated by large scatter and a rather
strong correlation between stellar age and GC content of galaxies in our
sample. We present evidence suggesting that the more important factor may be
the evolution of the LMXB population with time. Its effect is further amplified
by the larger GC content of older galaxies and correspondingly, the larger
numbers of dynamically formed binaries in them. We also found clear evolution
of the X-ray luminosity function (XLF) with age, that younger galaxies have
more bright sources and fewer faint sources per unit stellar mass. The XLF of
LMXBs in younger galaxies appears to extend significantly beyond E39 erg/s.
Such bright sources seem to be less frequent in older galaxies. We found that 6
out of ~ 12 (ultra-) luminous sources are located in GCs.
