The SLUGGS Survey: HST/ACS Mosaic Imaging of the NGC 3115 Globular
  Cluster System
  We present HST/ACS $g$ and $z$ photometry and half-light radii $R_{\rm h}$
measurements of 360 globular cluster (GC) candidates around the nearby S0
galaxy NGC 3115. We also include Subaru/Suprime-Cam $g$, $r$, and $i$
photometry of 421 additional candidates. The well-established color bimodality
of the GC system is obvious in the HST/ACS photometry. We find evidence for a
"blue tilt" in the blue GCs, wherein the blue GCs get redder as luminosity
increases, indicative of a mass-metallicity relationship. We find a color
gradient in both the red and blue subpopulations, with each group of clusters
becoming bluer at larger distances from NGC 3115. The gradient is of similar
strength in both subpopulations, but is monotonic and more significant for the
blue clusters. On average, the blue clusters have ~10% larger $R_{\rm h}$ than
the red clusters. This average difference is less than is typically observed
for early-type galaxies but does match that measured in the literature for
M104, suggesting that morphology and inclination may affect the measured size
difference between the red and blue clusters. However, the scatter on the
$R_{\rm h}$ measurements is large. We also identify 31 clusters more extended
than typical GCs, which we consider ultra-compact dwarf (UCD) candidates. Many
of these objects are fainter than typical UCDs. While it is likely that a
significant number will be background contaminants, six of these UCD candidates
are spectroscopically confirmed. To explore low-mass X-ray binaries in the GC
system, we match our ACS and Suprime-Cam detections to corresponding Chandra
X-ray sources. We identify 45 X-ray - GC matches, 16 among the blue
subpopulation and 29 among the red subpopulation. These X-ray/GC coincidence
fractions are larger than is typical for most GC systems, probably due to the
increased depth of the X-ray data compared to previous studies of GC systems.
