Using nebular near-IR spectroscopy to measure asymmetric chemical distributions in 2003fg-like thermonuclear supernovae

TL;DR

This study analyzes near-infrared spectra of 2003fg-like supernovae to reveal asymmetric inner chemical distributions, suggesting aspherical explosion mechanisms or progenitor systems.

Contribution

It provides the first detailed analysis of NIR spectral asymmetries in 2003fg-like SNe, linking line profiles to aspherical chemical distributions and explosion models.

Findings

Asymmetric [Fe II] line profiles are common in 2003fg-like SNe.

Line asymmetries are correlated within individual supernovae.

Results suggest aspherical inner ejecta distributions from specific progenitor scenarios.

Abstract

We present an analysis of three near-infrared (NIR; 1.0-2.4 $\mu$m) spectra of the SN 2003fg-like/"super-Chandrasekhar" type Ia supernovae (SNe Ia) SN 2009dc, SN 2020hvf, and SN 2022pul at respective phases +372, +296, and +294~d relative to the epoch of $B$-band maximum. We find that all objects in our sample have asymmetric, or "tilted", [Fe~II] 1.257 and 1.644 $\mu$m profiles. We quantify the asymmetry of these features using five methods: velocity at peak flux, profile tilts, residual testing, velocity fitting, and comparison to deflagration-detonation transition models. Our results demonstrate that, while the profiles of the [Fe II] 1.257 and 1.644 $\mu$m features are widely varied between 2003fg-likes, these features are correlated in shape within the same SN. This implies that line blending is most likely not the dominant cause of the asymmetries inferred from these profiles. Instead, it is more plausible that 2003fg-like SNe have aspherical chemical distributions in their inner regions. These distributions may come from aspherical progenitor systems, such as double white dwarf mergers, or off-center delayed-detonation explosions of Chandrasekhar-mass Carbon-Oxygen white dwarfs. Additional late-phase NIR observation of 2003fg-like SNe and detailed 3-D NLTE modeling of these two explosion scenarios are encouraged.