Abstract

We present integrated Washington CT1 photometry of the globular cluster system of NGC 4472 (M49), the brightest galaxy in the Virgo cluster. The photometry is deep, reaching beyond T-1 similar to R similar to 25 and allows us to investigate metallicities in the cluster system at an unprecedented level. We first examine the age, horizontal branch morphology and metallicity sensitivities of the integrated (C-T-1) color and reconfirm its utility as an efficient metal abundance index. As for other broadband colors, the index is much more sensitive to metallicity than age for old clusters (greater than or similar to 10 Gyr), but (C - T-1) has twice the metallicity sensitivity of (B - V) or (V-I). The metallicity calibration based on data for Galactic globular clusters yields metal abundances that are in good agreement with spectroscopically-derived values for extragalactic clusters as well. The metallicities of some 1800 of the best globular cluster candidates in NGC 4472 (similar to 1/4 of the total in this galaxy) are then derived from this calibration. These values are, on average, internally precise to 0.15 dex and accurate to similar to 0.2 dex. This is by far the largest dataset of accurate metal abundances available for any globular cluster system. The median metallicity of the system is [Fe/H]=-0.9+/-0.2 dex, where the error includes all sources of uncertainty in this value. More importantly, the color distribution is clearly bimodal, Assuming the color differences are determined by metallicity, the resulting metallicity distribution is very well-fit by two Gaussians with peaks at [Fe/H]similar to-1.3 and -0.1. In addition, the metal-rich clusters are significantly more concentrated to the center of NGC 4472 than their metal-poor counterparts. These results argue strongly for the presence of two distinct cluster populations and thus two distinct epochs and/or mechanisms of cluster formation, and are in agreement with the predictions of the Ashman Zepf [ApJ, 384, 50 (1992)] scenario of secondary globular cluster formation in mergers. As expected, there is a large metallicity dispersion in the globular clusters at any radius, amounting to sigma similar to 0.7 dex, and the clusters are more metal-poor than the background halo of the galaxy at all radii, by about 0.8 dex on average. The metallicity difference between the globulars and the halo increases with radius. The total cluster system displays a significant radial metallicity gradient of similar to 0.4 in Delta[Fe/H]/Delta log R, comparable to those uncovered in similar studies of other globular cluster systems. However, most of this gradient appears to be due to the varying radial concentration of the two populations. (C) 1996 American Astronomical Society.