Classical Type Ia Spectral Indicators from the Nearby Supernova Factory
Résumé
Type Ia supernovae (SNe Ia) make excellent cosmological distance indicators because of a standardization through light curve shape and color. Various spectral indicators have been proposed to further improve this standardization and refine SN Ia measurements for precision cosmology. We present measurements of spectral indicators proposed in the literature, including those that have been demonstrated to be correlated to light curve shape or intrinsic diversity, using spectrophotometric SN Ia spectra obtained by the Nearby Supernova Factory with the SuperNova Integral Field Spectrograph (SNIFS). In addition, we provide the correlation matrix between spectral and photometric indicators, probing the relevance of such indicators as equivalents to stretch and color. Most importantly, we probe, for the first time with large statistics, direct correlation of spectral indicators to Hubble diagram residuals --- independent of any proxy for luminosity such as stretch or decline-rate parameter.