A search for environmental effects on Type Ia supernovae

We use integrated colors and B and V absolute magnitudes of Type Ia superno va (SN) host galaxies in order to search for environmental effects on the S N optical properties. With the new sample of 44 SNe we confirm the conclusi on by Hamuy et al. that bright events occur preferentially in young stellar environments. We find also that the brightest SNe occur in the least lumin ous galaxies, a possible indication that metal-poor neighborhoods produce t he more luminous events. The interpretation of these results is made diffic ult, however, because of the fact that galaxies with younger stellar popula tions are also lower in luminosity. In an attempt to remove this ambiguity, we use models for the line strengths in the absorption spectrum of five ea rly-type galaxies, in order to estimate metallicities and ages of the SN ho st galaxies. With the addition of abundance estimates from nebular analysis of the emission spectra of three spiral galaxies, we find possible further evidence that luminous SNe are produced in metal-poor neighborhoods. Furth er spectroscopic observations of the SN host galaxies will be necessary to test these results and assist in disentangling the age and metallicity effe cts on Type Ia SNe.