Evidence for a correlation between the Si II 4000 width and Type Ia supernova color

TL;DR

This study finds a correlation between the Si II 4000 spectral feature width and the color of Type Ia supernovae, suggesting it could enhance distance measurement accuracy in cosmology.

Contribution

It introduces the Si II 4000 pseudo equivalent width as a new spectral indicator linked to supernova color and velocity evolution.

Findings

Si II 4000 width correlates with supernova color excess

Spectral indicator relates to spectroscopic subclasses and velocity gradient

Potential to improve cosmological distance estimates

Abstract

We study the pseudo equivalent width of the Si II 4000 feature of Type Ia supernovae in the redshift range 0.0024 < z < 0.634. We find that this spectral indicator correlates with the lightcurve color excess (SALT2 c) as well as previously defined spectroscopic subclasses (Branch types) and the evolution of the Si II 6150 velocity, i.e., the so called velocity gradient. Based on our study of 55 objects from different surveys, we find indications that the Si II 4000 spectral indicator could provide important information to improve cosmological distance measurements with Type Ia supernovae.