In this paper and a companion paper , we report on a wide-field imaging survey of the globular cluster ( GC ) populations around M87 carried out with Suprime-Cam on the 8.2m Subaru telescope .
Here we describe the observations , data reduction , and data analysis and present luminosity functions of GC populations around M87 and NGC 4552 , another luminous Virgo elliptical in our survey field .
The imaging data were taken in the B , V , and I bands with a sky coverage of 2 ^ { \circ } \times 0 _ { \cdot } ^ { \circ } 5 extending from the M87 centre out to \sim 0.5 Mpc .
GC candidates were selected by applying a colour criterion on the B - V and V - I diagram to unresolved objects , which greatly reduces contamination .
The data from control fields taken with Subaru/Suprime-Cam were also analyzed for subtraction of contamination in the GC sample .
These control field data are compatible with those in the M87 field in terms of the filter set ( BVI ) , limiting magnitudes , and image quality , which minimizes the possibility of introducing any systematic errors into the subtractive correction .
We investigate GC luminosity functions ( GCLFs ) at distances \leq 10 ^ { \prime } ( \lesssim 45 kpc ) from the host galaxy centre in detail .
By fitting Gaussians to the GCLFs , the V -band turnover magnitude ( V _ { TO } ) is estimated to be 23.62 \pm 0.06 mag and 23.56 \pm 0.20 mag for the GC population in M87 and NGC 4552 , respectively .
The GCLF is found to be a function of GC colour ; V _ { TO } of the red GC subpopulation ( V - I > 1.1 ) is fainter than that of the blue GC subpopulation ( V - I \leq 1.1 ) in both M87 and NGC 4552 , as expected if the colour differences are primarily due to a metallicity effect and the mass functions of the two subpopulations are similar .
The radial dependence of the GCLF is also investigated for the GC population in M87 .
The GCLF of each subpopulation at 1 ^ { \prime } \leq R \leq 5 ^ { \prime } is compared with that at 5 ^ { \prime } \leq R \leq 10 ^ { \prime } but no significant trend with distance is found in the shape of the GCLF .
We also estimate GC specific frequencies ( S _ { N } ) for M87 and NGC 4552 .
The S _ { N } of the M87 GC population is estimated to be 12.5 \pm 0.8 within 25 ^ { \prime } .
The S _ { N } value of the NGC 4552 GC population is estimated to be 5.0 \pm 0.6 within 10 ^ { \prime } .