Spectroscopic Properties of Star-Forming Host Galaxies and Type Ia
  Supernova Hubble Residuals in a Nearly Unbiased Sample
  We examine the correlation between supernova host galaxy properties and their
residuals on the Hubble diagram. We use supernovae discovered during the Sloan
Digital Sky Survey II - Supernova Survey, and focus on objects at a redshift of
z < 0.15, where the selection effects of the survey are known to yield a
complete Type Ia supernova sample. To minimize the bias in our analysis with
respect to measured host-galaxy properties, spectra were obtained for nearly
all hosts, spanning a range in magnitude of -23 < M_r < -17. In contrast to
previous works that use photometric estimates of host mass as a proxy for
global metallicity, we analyze host-galaxy spectra to obtain gas-phase
metallicities and star-formation rates from host galaxies with active star
formation. From a final sample of ~ 40 emission-line galaxies, we find that
light-curve corrected Type Ia supernovae are ~ 0.1 magnitudes brighter in
high-metallicity hosts than in low-metallicity hosts. We also find a
significant (> 3{\sigma}) correlation between the Hubble residuals of Type Ia
supernovae and the specific star-formation rate of the host galaxy. We comment
on the importance of supernova/host-galaxy correlations as a source of
systematic bias in future deep supernova surveys.
