On the origin of the color-magnitude relation in the Virgo Cluster

We explore the origin of the color-magnitude relation (CMR) of early-type g alaxies in the Virgo Cluster using spectra of very high signal-to-noise rat io for six elliptical galaxies selected along the CMR. The data are analyze d using a new evolutionary stellar population synthesis model to generate g alaxy spectra at the resolution given by their velocity dispersions. In par ticular, we use a new age indicator that is virtually free of the effects o f metallicity. We find that the luminosity-weighted mean ages of Virgo elli pticals are greater than similar to8 Gyr and show no clear trend with galax y luminosity. We also find a positive correlation of metallicity with lumin osity, color, and velocity dispersion. We conclude that the CMR is driven p rimarily by a luminosity-metallicity correlation. However, not all elements increase equally with the total metallicity, and we speculate that the CMR may be driven by both a total metallicity increase and a systematic depart ure from solar abundance ratios of some elements along the CMR. A full unde rstanding of the role played by the total metallicity, abundance ratios, an d age in generating the CMR requires the analysis of spectra of very high q uality, such as those reported here, for a larger number of galaxies in Vir go and other clusters.