Globular cluster population of the HST frontier fields galaxy
  J07173724+3744224
  We present the first measurement of the globular cluster population
surrounding the elliptical galaxy J07173724+3744224 (z=0.1546). This galaxy is
located in the foreground in the field-of-view of the Hubble Space Telescope
(HST) Frontier Fields observations of galaxy cluster MACS J0717.5+3745
(z=0.5458). Based on deep HST ACS F435W, F606W, and F814W images, we find a
total globular cluster population of N_tot = 3441 +/- 1416. Applying the
appropriate extinction correction and filter transformation from ACS F814W to
the Johnson V-band, we determine that the host galaxy has an absolute magnitude
of M_V = -22.2. The specific frequency was found to be S_N = 4.5 +/- 1.8. The
radial profile of the globular cluster system was best fit using a powerlaw of
the form $\sigma\sim R^{-0.6}$, with the globular cluster population found to
be more extended than the halo light of the host galaxy ($\sigma_{halo}\sim
R^{-1.7}$). The F435W-F814W colour distribution suggests a bimodal population,
with red globular clusters 1-3x more abundant than blue clusters. These results
are consistent with the host elliptical galaxy J07173724+3744224 having formed
its red metal-rich GCs in situ, with the blue metal-poor globular clusters
accreted from low-mass galaxies.
