A statistical analysis of circumstellar material in Type Ia supernovae

TL;DR

This study analyzes the presence and characteristics of circumstellar material in Type Ia supernovae using spectral data, revealing a significant subset with blueshifted Na I D absorption linked to specific host galaxy types and supernova properties.

Contribution

It provides new spectral observations and confirms the existence of a subset of SNe Ia with circumstellar material, supporting the idea of multiple progenitor populations.

Findings

Approximately 20% of SNe Ia show blueshifted Na I D absorption.

Host galaxies of these SNe are skewed towards later types.

Blueshifted Na I D strength correlates with SN color and is stronger than in non-blueshifted cases.

Abstract

A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material (CSM) surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the ESO Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (~20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to non-blueshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption, and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B-V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests there are at least two distinct populations of normal, cosmologically useful SNe Ia.