Abstract
ABSTRACT This work aims to study different probes of Type Ia supernova (SN Ia) progenitors that have been suggested to be linked to the presence of circumstellar material (CSM). In particular, we have investigated, for the first time, the link between narrow blueshifted Na i D absorption profiles and the presence and strength of the broad high-velocity Ca ii near-infrared triplet absorption features seen in SNe Ia around maximum light. With the probes exploring different distances from the SN; Na i D > 1017cm, high-velocity Ca ii features < 1015cm. For this, we have used a new intermediate-resolution X-shooter spectral sample of 15 SNe Ia. We do not identify a link between these two probes, implying either that, one (or both) is not physically related to the presence of CSM or that the occurrence of CSM at the distance explored by one probe is not linked to its presence at the distance probed by the other. However, the previously identified statistical excess in the presence of blueshifted (over redshifted) Na i D absorption is confirmed in this sample at high significance and is found to be stronger in SNe Ia hosted by late-type galaxies. This excess is difficult to explain as being from an interstellar-medium origin as has been suggested by some recent modelling, as such an origin is not expected to show a bias for blueshifted absorption. However, a circumstellar origin for these features also appears unsatisfactory based on our new results, given the lack of link between the two probes of CSM investigated.
Highlights
Type Ia supernovae (SNe Ia) are the explosions of white dwarfs in binary systems, play a major role in our understanding of the expansion rate of the Universe and are essential for constraining the properties of dark energy to high precision (e.g. Scolnic et al 2018)
Our main conclusions are as follows: (i) We confirmed a %EB of 23 per cent blueshifted over redshifted Na I D features in a new sample of maximum-light SN Ia intermediate-resolution spectra, in agreement with previous studies
(iii) We did not identify a trend between the presence or strength of high-velocity Ca II features seen in the majority of SNe Ia around maximum light and the presence of narrow blueshifted Na I D features
Summary
Type Ia supernovae (SNe Ia) are the explosions of white dwarfs in binary systems, play a major role in our understanding of the expansion rate of the Universe and are essential for constraining the properties of dark energy to high precision (e.g. Scolnic et al 2018). Classical SN Ia models involve an exploding white dwarf that is close to the Chandrasekhar mass, which has accreted matter from a non-degenerate companion star and resulting in a runaway thermonuclear reaction (Whelan, Iben & Iben 1973). One observational method that has been used to distinguish between potential SN Ia progenitor scenarios is the presence of circumstellar material (CSM), which is thought to be more likely in the case of a non-degenerate companion star (Hachisu et al 1999a; Hachisu, Kato & ichi Nomoto 1999b), may be present in some merger scenarios An excess of blueshifted compared to redshifted Na I D absorption features has been identified in larger SN Ia samples, consistent with a CSM origin in ∼20 per cent of SNe Ia (Sternberg et al 2011; Maguire et al 2013)
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