We have performed a wide-field imaging survey of the globular cluster ( GC ) populations around M87 with Suprime-Cam on the 8.2m Subaru Telescope .
A 2 ^ { \circ } \times 0 _ { \cdot } ^ { \circ } 5 field extending from the centre of M87 out to a radius of \sim 0.5 Mpc was observed through the BVI filters .
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 } \sim 1.0 and 1.2 ) is seen only in the inner regions ( \lesssim 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 \leq 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 \sim 0.5 Mpc from M87 by a superposition of the GC populations associated with M87 and with NGC 4552 .
It is found that there are some regions where the GC surface densities are larger than expected from this model , suggesting the existence of an additional intergalactic GC ( i-GC ) population independent of the luminous ellipticals .
By comparing the estimated i-GC surface density with the luminosity density of the intracluster stellar population inferred from the intergalactic planetary nebulae in the Virgo cluster , we obtain a crude estimate of i-GC specific frequency S _ { N } = 2.9 ^ { +4.2 } _ { -1.5 } .
If this S _ { N } value represents the stellar population tidally stripped by a massive central galaxy from other ( less luminous ) galaxies , the contribution of tidally captured GCs in the GC population of M87 would need to be low to be consistent with the high S _ { N } value of M87 .