He II recombination lines as a test of the nature of SN Ia progenitors in elliptical galaxies

TL;DR

This paper proposes using He II recombination lines as a novel method to determine whether single degenerate progenitors significantly contribute to Type Ia supernovae in elliptical galaxies by analyzing their ionizing UV radiation.

Contribution

It introduces a new observational approach to constrain SN Ia progenitor models through He II emission line measurements in early-type galaxies.

Findings

Single degenerate progenitors would produce a ten-fold increase in He II-ionizing UV radiation.

He II emission line upper limits can constrain the contribution of single degenerate channels.

The method offers a new way to differentiate progenitor scenarios in old stellar populations.

Abstract

To date, the question of which progenitor channel can reproduce the observed rate of Type Ia supernovae (SNe Ia) remains unresolved, with the single and double degenerate scenarios remaining the leading contenders. The former implies a large population of hot accreting white dwarfs with photospheric temperatures of T ~ 10^5-10^6 K during some part of their accretion history. We show that in early-type galaxies, a population of accreting white dwarfs large enough to reproduce the SN Ia rate would contribute significantly to the ionizing UV radiation expected from the stellar population. For mean stellar ages < ~5 Gyr, single degenerate progenitors would dominate the ionizing background produced by stars, increasing the continuum beyond the He II-ionizing limit more than ten-fold. This opens a new avenue for constraining the progenitors of SNe Ia, through consideration of the spatially extended low-ionization emission-line regions now found in many early-type galaxies. Modelling the expected emission, we show that one can constrain the contribution of the single degenerate channel to the SN Ia rate in E/S0 galaxies from upper limits on the luminosity of He II recombination lines in the optical and FUV. We discuss future directions, as well as possible implications for the evolution of SNe Ia in old stellar populations.