Type Ia Supernova Hubble Residuals and Host-Galaxy Properties
  Kim et al. (2013) [K13] introduced a new methodology for determining
peak-brightness absolute magnitudes of type Ia supernovae from multi-band light
curves. We examine the relation between their parameterization of light curves
and Hubble residuals, based on photometry synthesized from the Nearby Supernova
Factory spectrophotometric time series, with global host-galaxy properties. The
K13 Hubble residual step with host mass is $0.013\pm 0.031$ mag for a supernova
subsample with data coverage corresponding to the K13 training; at $\ll
1\sigma$, the step is not significant and lower than previous measurements.
Relaxing the data coverage requirement the Hubble residual step with host mass
is $0.045\pm 0.026$ mag for the larger sample; a calculation using the modes of
the distributions, less sensitive to outliers, yields a step of 0.019 mag. The
analysis of this article uses K13 inferred luminosities, as distinguished from
previous works that use magnitude corrections as a function of SALT2 color and
stretch parameters: Steps at $>2\sigma $ significance are found in SALT2 Hubble
residuals in samples split by the values of their K13 $x(1)$ and $x(2)$
light-curve parameters. $x(1)$ affects the light-curve width and color around
peak (similar to the $\Delta m_{15}$ and stretch parameters), and $x(2)$
affects colors, the near-UV light-curve width, and the light-curve decline 20
to 30 days after peak brightness. The novel light-curve analysis, increased
parameter set, and magnitude corrections of K13 may be capturing features of
SN~Ia diversity arising from progenitor stellar evolution.
