THE LOCAL HOSTS OF TYPE Ia SUPERNOVAE

We use multi-wavelength, matched aperture, integrated photometry from the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the RC3 to estimate the physical properties of 166 nearby galaxies hosting 168 well-observed Type Ia supernovae (SNe Ia). The ultraviolet (UV) imaging of local SN Ia hosts from GALEX allows a direct comparison with higher-redshift hosts measured at optical wavelengths that correspond to the rest-frame UV. Our data corroborate well-known features that have been seen in other SN Ia samples. Specifically, hosts with active star formation produce brighter and slower SNe Ia on average, and hosts with luminosity-weighted ages older than 1 Gyr produce on average more faint, fast, and fewer bright, slow SNe Ia than younger hosts. New results include that in our sample, the faintest and fastest SNe Ia occur only in galaxies exceeding a stellar mass threshold of similar to 10(10) M(circle dot), leading us to conclude that their progenitors must arise in populations that are older and/or more metal rich than the general SN Ia population. A low host extinction subsample hints at a residual trend in peak luminosity with host age, after correcting for light-curve shape, giving the appearance that older hosts produce less-extincted SNe Ia on average. This has implications for cosmological fitting of SNe Ia, and suggests that host age could be useful as a parameter in the fitting. Converting host mass to metallicity and computing (56)Ni mass from the supernova light curves, we find that our local sample is consistent with a model that predicts a shallow trend between stellar metallicity and the (56)Ni mass that powers the explosion, but we cannot rule out the absence of a trend. We measure a correlation between (56)Ni mass and host age in the local universe that is shallower and not as significant as that seen at higher redshifts. The details of the age-(56)Ni mass correlations at low and higher redshift imply a luminosity-weighted age threshold of similar to 3 Gyr for SN Ia hosts, above which they are less likely to produce SNe Ia with (56)Ni masses above similar to 0.5 M(circle dot).