Type Ia Supernovae: Colors, Rates, and Progenitors

TL;DR

This study demonstrates that galaxy colors and luminosity can accurately predict SN Ia rates, supporting a continuous delay time distribution that favors the double degenerate progenitor scenario, with some distinctions for supernova stretch types.

Contribution

It introduces a simple method to determine SN Ia rates from observable galaxy properties, and provides observational evidence supporting a continuous delay time distribution.

Findings

SN Ia rates can be predicted from host galaxy color and luminosity.

The delay time distribution is consistent with a power-law slope of approximately -1.5.

Results favor the double degenerate progenitor scenario for SNe Ia.

Abstract

The rate of type Ia supernovae (SNe Ia) in a galaxy depends not only on stellar mass, but also on star formation history. Here we show that two simple observational quantities ($g-r$ or $u-r$ host galaxy color, and $r$-band luminosity), coupled with an assumed delay time distribution (the rate of SNe Ia as a function of time for an instantaneous burst of star formation), are sufficient to accurately determine a galaxy's SN Ia rate, with very little sensitivity to the precise details of the star formation history. Using this result, we compare observed and predicted color distributions of SN Ia hosts for the MENeaCS cluster supernova survey, and for the SDSS Stripe 82 supernova survey. The observations are consistent with a continuous delay time distribution (DTD), without any cutoff. For old progenitor systems the power-law slope for the DTD is found to be $-1.50 ^{+0.19} _{-0.15}$. This result favours the double degenerate scenario for SN Ia, though other interpretations are possible. We find that the late-time slopes of the delay time distribution are different at the 1$\sigma$ level for low and high stretch supernova, which suggest a single degenerate scenario for the latter. However, due to ambiguity in the current models' DTD predictions, single degenerate progenitors can neither be confirmed as causing high stretch supernovae nor ruled out from contributing to the overall sample.