Subluminous Type Ia Supernovae at High Redshift from the Supernova Legacy Survey

TL;DR

This study analyzes the rate evolution of subluminous Type Ia supernovae at high redshift, finding a constant or decreasing rate with redshift, mainly in early-type galaxies, contrasting with the increasing rate of normal SNe Ia.

Contribution

It provides the first measurement of the high-redshift rate evolution of subluminous SNe Ia, highlighting their dependence on galaxy mass and environment.

Findings

Subluminous SNe Ia rate is constant or slightly decreasing up to z=0.6.

Most subluminous SNe Ia are found in early-type, low star formation galaxies.

Rate correlates with galaxy mass, $r(z)=A imes M_g$.

Abstract

The rate evolution of subluminous Type Ia Supernovae is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly-declining light-curves of the observed supernova Ia (SN Ia) population here defined by low stretch values (s<0.8). Up to redshift z=0.6, we find 18 photometrically-identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically-confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behaviour is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass dependent behavior: $r(z)=A\times M_g$, with $A=(1.1\pm0.3)\times10^{-14}$ SNe per year and solar mass.