Probing the GC-LMXB connection in NGC 1399: a wide-field study with HST
  and Chandra
  We present a wide field study of the Globular Clusters/Low Mass X-ray Binary
(LMXB) connection in the giant elliptical NGC1399. The large FOV of the
ACS/WFC, combined with the HST and Chandra high resolution, allow us to
constrain the LMXB formation scenarios in elliptical galaxies. We confirm that
NGC1399 has the highest LMXB fraction in GCs of all nearby elliptical galaxies
studied so far, even though the exact value depends on galactocentric distance
due to the interplay of a differential GC vs galaxy light distribution and the
GC color dependence. In fact LMXBs are preferentially hosted by bright, red GCs
out to $>5 R_{eff}$ of the galaxy light. The finding that GC hosting LMXBs
follow the radial distribution of their parent GC population, argues against
the hypothesis that the external dynamical influence of the galaxy affects LMXB
formation in GCs. On the other hand field LMXBs closely match the host galaxy
light, thus indicating that they are originally formed in situ and not inside
GCs. We measure GC structural parameters, finding that the LMXB formation
likelihood is influenced independently by mass, metallicity and GCs structural
parameters. In particular the GC central density plays a major role in
predicting which GC host accreting binaries. Finally our analysis shows that
LMXBs in GCs are marginally brighter than those in the field, and in particular
the only color-confirmed GC with $L_X>10^{39}$ erg s$^{-1}$ shows no
variability, which may indicate a superposition of multiple LMXBs in these
systems.
