The Local Hosts of Type Ia Supernovae
  We use multi-wavelength, matched aperture, integrated photometry from GALEX,
SDSS and the RC3 to estimate the physical properties of 166 nearby galaxies
hosting 168 well-observed Type Ia supernovae (SNe Ia). 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 threshhold of ~10^10 M_sun, indicating 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 sub-sample 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 56Ni 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 56Ni
mass that powers the explosion, but we cannot rule out the absence of a trend.
We measure a correlation between 56Ni 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 -- 56Ni mass correlations at low and higher redshift imply a
luminosity-weighted age threshhold of ~3 Gyr for SN Ia hosts, above which they
are less likely to produce SNe Ia with 56Ni masses above ~0.5 M_sun. (Abridged)
