A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 - I. Observation, data analysis and luminosity function

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 8.2-m 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 degrees x 0 degrees.5 extending from the M87 centre out to similar to 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 analysed 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 minimize the possibility of introducing any systematic errors into the subtractive correction. We investigate GC luminosity functions (GCLFs) at distances <= 10 arcmin (less than or similar to 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 +/- 0.06 and 23.56 +/- 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 <= 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 <= R <= 5 arcmin is compared to that at 5 <= R <= 10 arcmin, 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 +/- 0.8 within 25 arcmin. The S-N of the NGC 4552 GC population is estimated to be 5.0 +/- 0.6 within 10 arcmin.