Better age estimation using ultraviolet–optical colours: breaking the age–metallicity degeneracy

• Published in: Monthly notices of the Royal Astronomical Society. Letters Vol. 381; no. 1; pp. L74 - L78
• Main Authors: Kaviraj, S., Rey, S.-C., Rich, R. M., Yoon, S.-J., Yi, S. K.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-10-2007
• Subjects: galaxies: elliptical and lenticular; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: fundamental parameters
• ISSN: 1745-3925; 1745-3933
• DOI: 10.1111/j.1745-3933.2007.00370.x

We demonstrate that the combination of GALEX ultraviolet (UV) photometry in the far-UV (FUV; ∼1530 Å) and near-UV (NUV; ∼2310 Å) 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 globular clusters (GCs) in M31, and show that the full set of FUV, NUV, U,B,V,R,I photometry produces age estimates that are ∼90 per cent more constrained and metallicity estimates that are ∼60 per cent 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 spectroscopic indices.