The Evolution of the Type Ia Supernova Luminosity Function

TL;DR

This paper investigates how the luminosity of Type Ia supernovae correlates with stellar age, using observational data and population synthesis models, and finds that double white dwarf systems can explain the observed diversity and evolution.

Contribution

It demonstrates that prompt detonations of sub-Chandrasekhar mass white dwarfs in double WD systems can reproduce the observed luminosity-age relationship of SNe Ia.

Findings

Fainter SNe Ia occur in older stellar populations.

Double WD systems with less massive primaries produce fainter SNe Ia.

Prompt detonations in double WD systems match the evolution of the luminosity function.

Abstract

Type Ia supernovae (SNe Ia) exhibit a wide diversity of peak luminosities and light curve shapes: the faintest SNe Ia are 10 times less luminous and evolve more rapidly than the brightest SNe Ia. Their differing characteristics also extend to their stellar age distributions, with fainter SNe Ia preferentially occurring in old stellar populations and vice versa. In this Letter, we quantify this SN Ia luminosity - stellar age connection using data from the Lick Observatory Supernova Search (LOSS). Our binary population synthesis calculations agree qualitatively with the observed trend in the >1 Gyr-old populations probed by LOSS if the majority of SNe Ia arise from prompt detonations of sub-Chandrasekhar mass white dwarfs (WDs) in double WD systems. Under appropriate assumptions, we show that double WD systems with less massive primaries, which yield fainter SNe Ia, interact and explode at older ages than those with more massive primaries. We find that prompt detonations in double WD systems are capable of reproducing the observed evolution of the SN Ia luminosity function, a constraint that any SN Ia progenitor scenario must confront.