The Effect of Host Galaxies on Type Ia Supernovae in the SDSS-II
  Supernova Survey
  We present an analysis of the host galaxy dependencies of Type Ia Supernovae
(SNe Ia) from the full three year sample of the SDSS-II Supernova Survey. We
rediscover, to high significance, the strong correlation between host galaxy
typeand the width of the observed SN light curve, i.e., fainter, quickly
declining SNe Ia favor passive host galaxies, while brighter, slowly declining
Ia's favor star-forming galaxies. We also find evidence (at between 2 to 3
sigma) that SNe Ia are ~0.1 magnitudes brighter in passive host galaxies, than
in star-forming hosts, after the SN Ia light curves have been standardized
using the light curve shape and color variations: This difference in brightness
is present in both the SALT2 and MCLS2k2 light curve fitting methodologies. We
see evidence for differences in the SN Ia color relationship between passive
and star-forming host galaxies, e.g., for the MLCS2k2 technique, we see that
SNe Ia in passive hosts favor a dust law of R_V ~1, while SNe Ia in
star-forming hosts require R_V ~2. The significance of these trends depends on
the range of SN colors considered. We demonstrate that these effects can be
parameterized using the stellar mass of the host galaxy (with a confidence of
>4 sigma) and including this extra parameter provides a better statistical fit
to our data. Our results suggest that future cosmological analyses of SN Ia
samples should include host galaxy information.
