Better Age Estimations Using Uv-optical Colours: Breaking the Age-metallicity Degeneracy

We demonstrate that the combination of GALEX UV photometry in the FUV (∼ 1530 angstroms) and NUV (∼ 2310 angstroms) passbands with optical photometry in the standard U,B, V,R, I filters can efficiently break the age-metallicity degeneracy. We estimate well-constrained ages, metallicities and their associated errors for 42 GCs in M31, and show that the full set of FUV,NUV,U,B, V,R, I photometry produces age estimates that are ∼ 90 percent more constrained and metallicity estimates that are ∼ 60 percent more constrained than those produced by using optical filters alone. The quality of the age constraints is comparable or marginally better than those achieved using a large number of spectrscopic indices. Subject headings: galaxies: early-type and lenticular, cD — galaxies: formation — galaxies: evolution