1999AJ....118.2734P

The age difference between the two main globular cluster subpopulations in the Virgo giant elliptical galaxy NGC 4472 (M49) has been determined using Hubble Space Telescope WFPC2 images in the F555W and F814W filters. Accurate photometry has been obtained for several hundred globular clusters in each of the two main subpopulations, down to more than 1 mag below the turnover of their luminosity functions. This allows precise determinations of both the mean colors and the turnover magnitudes of the two main subpopulations. By comparing the data with various population synthesis models, the age-metallicity pairs that fit both the observed colors and magnitudes have been identified. The metal-poor and the metal-rich globular clusters are found to be coeval within the errors (∼3 Gyr). If one accepts the validity of our assumptions, these errors are dominated by model uncertainties. A systematic error of up to 4 Gyr could affect this result if the blue and the red clusters have significantly different mass distributions. However, that one subpopulation is half as old as the other is excluded at the 99% confidence level. The different globular cluster populations are assumed to trace the galaxy's major star formation episodes. Consequently, the vast majority of globular clusters (and by implication the majority of stars) in NGC 4472 formed at high redshifts but by two distinct mechanisms or in two episodes. The distance to NGC 4472 is determined to be 15.8±0.8 Mpc, which is in excellent agreement with six of the seven Cepheid distances to Virgo Cluster spiral galaxies. This implies that the spiral and elliptical galaxies in the main body of Virgo are at the same distance.