Washington CCD photometry of the globular cluster system of the giant elliptical galaxy M60 in Virgo

We present a photometric study of the GCs in the giant elliptical galaxy M60 in the Virgo Cluster, based on deep, relatively wide field Washington CT1 CCD images. The CMD reveals a significant population of GCs in M60 and a large number of young luminous clusters in NGC 4647, a small companion spiral northwest of M60. The color distribution of the GCs in M60 is clearly bimodal, with a blue peak at ( C - T-1) 1: 37 and a red peak at ( C - T1) 1: 87. We derive two new transformation relations between the ( C - T1) 0 color and [ Fe/H] using the data for the GCs in our Galaxy and M49. Using these relations, we derive the metallicity distribution of the GCs in M60, which is also bimodal: a dominant metal-poor component with center at [Fe/H] = -1.2, and a weaker metal-rich component with center at [Fe/H] = -0.2. The radial number density profile of the GCs is more extended than that of the stellar halo, and the radial number density profile of the blue GCs is more extended than that of the red GCs. The number density maps of the GCs show that the spatial distribution of the blue GCs is roughly circular, while that of the red GCs is elongated similarly to that of the stellar halo. We estimate the total number of the GCs in M60 to be 3600 +/- 500 and the specific frequency to be S-N 3.8 +/- 0.4. The mean color of the bright blue GCs gets redder as they get brighter in both the inner and outer region of M60. This blue tilt is seen also in the outer region of M49, the brightest Virgo galaxy. Implications of these results are discussed.