  We have performed a wide-field imaging survey of the globular cluster (GC)
populations around M87 out to a radius of ~ 0.5 Mpc with Suprime-Cam on the
8.2m Subaru Telescope. By investigating the GC colour distribution as a
function of distance from M87 and NGC 4552, another luminous Virgo elliptical
in our survey field, it is found that clear bimodality ((V-I)_peak ~ 1.0 and
1.2) is seen only in the inner regions (< 10 kpc) of the host galaxies and that
it becomes weaker with radius due to the decreasing contribution of the red GC
(V-I > 1.1) subpopulation. It is also found (both around M87 and NGC 4552) that
while the spatial distribution of the red GCs is as centrally concentrated as
the host galaxy halo light distribution, the distribution of the blue GCs (V-I
< 1.1) tends to be more extended. However, the blue GC distribution around M87
is not as extended as the Virgo cluster mass density profile. Based on these
facts, we argue that the contribution of GCs associated with the Virgo cluster
(e.g., intergalactic GCs) is not significant around M87 and is not the primary
reason for the high S_N value of M87. Instead, most of the blue GCs around
luminous ellipticals, as well as the red GCs, are presumed to be associated
with the host galaxy. We model the radial profile of GC surface densities out
to ~ 0.5 Mpc from M87 by a superposition of the GC populations associated with
M87 and with NGC 4552, suggesting the existence of an additional intergalactic
GC (i-GC) population independent of the luminous ellipticals. We obtain a crude
estimate of i-GC specific frequency S_N = 2.9 (+4.2, -1.5), which may indicate
the contribution of tidally captured GCs in the GC population of M87 is low to
be consistent with the high S_N value of M87.
