Galaxy structure from multiple tracers: I. A census of M87's globular
  cluster populations
  We present a new photometric catalogue of the rich globular cluster (GC)
system around M87, the brightest cluster galaxy in Virgo. Using archival Next
Generation Virgo cluster Survey (NGVS) images in the ugriz bands, observed with
CFHT/MegaPrime, we perform a careful subtraction of the galaxy's halo light in
order to detect objects at small galactocentric radii as well as in the wider
field, and find 17620 GC candidates over a radius range from 1.3 kpc to 445 kpc
with g < 24 magnitudes. By inferring their colour, radial and magnitude
distributions in a Bayesian way, we find that they are well described as a
mixture of two GC populations and two distinct contaminant populations, but
confirm earlier findings of radius-dependent colour gradients in both GC
populations. This is consistent with a picture in which the more enriched GCs
reside deeper in the galaxy's potential well, indicating a role for dissipative
collapse in the formation of both the red and the blue GCs.
