Photometric Metallicities in dSphs

Joanne D. Hughes
Seattle University

ABSTRACT

We examine photometric estimates of metallicities within local dwarf galaxies. In determining the most practical combination of Washington, Strömgren and SDSS filters for characterizing the stellar content of several local dSphs, we find that the SDSS filters have less than half the [Fe/H]-sensitivity of the Washington filters. As expected, the Strömgren m1-index gives a more-accurate metallicity estimate than the Washington filters for the individual upper-RGB stars, but only if 1% photometry is achieved. In many of the SDSS-discovered dSphs, the upper RGB is very sparsely populated. The metallicity/temperature combination for very metal-poor stars on the lower RGB leads to a loss of [Fe/H]-resolution for the m1-index, necessitating the search for a more robust filter combination to break the age/metallicity degeneracy in these important stellar populations.