Type Ia supernova hubble residuals and host-galaxy properties

Kim et al. (2013) [K13] introduced a new methodology for determining peak- brightness absolute magnitudesof type Ia supernovaefrom multi-band light curves. We examine the relation between their parameterization of light curvesand Hubble residuals, based on photometry synthesized from the Nearby SupernovaFactory spec- trophotometric time series, with global host-galaxy properties. The K13 Hubble residual step with host mass is 0.013 ? 0.031 mag for a supernovasubsample with data coverage corresponding to the K13 training; at ? 1?, 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 ? 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 param- eters: Steps at > 2? significance are found in SALT2 Hubble residuals in samples split by the values of their K13 x(1) and x(2) light-curveparameters. x(1) affects the light- curvewidth and color around peak (similar to the ∆m15 and stretch parameters), and x(2) affects colors, the near-UV light-curvewidth, and the light-curvedecline 20 to 30 days after peak brightness. The novel light-curveanalysis, increased parameter set, and magnitude corrections of K13 may be capturing features of SN Ia diversity arising from progenitor stellar evolution.