Abstract:
Recent Chandra studies of low-mass X-ray binaries (LMXBs) within early-type galaxies have found that
LMXBs are commonly located within globular clusters of the galaxies. However, whether all LMXBs are formed
within globular clusters has remained an open question. If all LMXBs formed within globular clusters, the summed
X-ray luminosity of the LMXBs in a galaxy should be directly proportional to the number of globular clusters in the
galaxy regardless of where the LMXBs currently reside. We have compared these two quantities over the same
angular area for a sample of 12 elliptical and S0 galaxies observed with Chandra and found that the correlation
between the two quantities is weaker than expected if all LMXBs formed within globular clusters. This indicates
that a significant number of the LMXBs were formed in the field and naturally accounts for the spread in field-tocluster
fractions of LMXBs from galaxy to galaxy. We also find that the ‘‘pollution’’ of globular cluster LMXBs into
the field has been minimal within elliptical galaxies, but there is evidence that roughly half of the LMXBs originally in
the globular clusters of S0 galaxies in our sample have escaped into the field. This is likely due to higher globular
cluster disruption rates in S0s, resulting from stronger gravitational shocks caused by the passage of globular clusters
through the disks of S0 galaxies that are absent in elliptical galaxies.
