The Large-Scale Environments of Type Ia Supernovae: Evidence for a
  Metallicity Bias in the Rate or Luminosity of Prompt Ia Events
  Using data drawn from the Sloan Digital Sky Survey (SDSS) and the SDSS-II
Supernova Survey, we study the local environments of confirmed type Ia
supernovae (SNe Ia) in the nearby Universe. At 0.05 < z < 0.15, we find that SN
Ia events in blue, star-forming galaxies occur preferentially in regions of
lower galaxy density relative to galaxies of like stellar mass and
star-formation rate, while SNe Ia in nearby red galaxies show no significant
environment dependence within the measurement uncertainties. Even though our
samples of SNe in red hosts are relatively small in number, tests on simulated
galaxy samples suggest that the observed distribution of environments for red
SN Ia hosts is in poor agreement with a cluster type Ia rate strongly elevated
relative to the field rate. Finally, after considering the impact of galaxy
morphology, stellar age, stellar metallicity, and other relevant galaxy
properties, we conclude that the observed correlation between the SN Ia rate
and environment in the star-forming galaxy population is likely driven by a
gas-phase metallicity effect, such that prompt type Ia supernovae occur more
often or are more luminous in metal-poor systems.
