M87 globular clusters BVI photometry

Our measured sample comprises 270 objects brighter than V~23.4mag and with distances r>25" (>2kpc) from the center of the galaxy. In agreement with the recent study of Cohen, we find no detectable gradient of mean cluster color (metallicity) in (B-V) or (V-I) with radial distance.

The cluster system does, however, display a large dispersion in color at any radius, corresponding to sigma([Fe/H])~0.6 about a mean metallicity (Fe/H]>~-1.1 according to our color index scale. The difference in mean color between the globular clusters and the underlying halo light of the galaxy itself, found previously by Strom and coworkers and by Cohen, shows up strongly in all of our color indices; we find virtually no clusters as red as mean color of the halo stars at any radius.