Progenitor mass and ejecta asymmetry of SN 2023ixf from nebular spectroscopy

TL;DR

This study uses nebular spectroscopy taken 259 days after SN 2023ixf's explosion to estimate its progenitor star's mass, revealing a low-mass star of 12-15 solar masses and indicating asymmetric ejecta.

Contribution

It provides an independent nebular spectroscopic analysis to constrain the progenitor mass, complementing previous hydrodynamical and imaging studies.

Findings

Progenitor mass estimated between 12 and 15 solar masses.

Evidence of asymmetric ejecta from line profile analysis.

Results support a low-mass progenitor consistent with prior models.

Abstract

Context. SN 2023ixf was discovered in Galaxy M101 in May 2023. Its proximity made it an extremely valuable opportunity for the scientific community to study the characteristics of the SN and its progenitor. A point source detected on archival images and hydrodynamical modelling of the bolometric light curve has been used to constrain the former star's properties. There is a significant variation in the published results regarding the initial mass of the progenitor. Nebular spectroscopy provides an independent tool to enhance our understanding of the supernova and its progenitor. Aims. We determine the SN progenitor mass by studying the first published nebular spectrum taken 259 days after the explosion. Methods. We analyze the nebular spectrum taken with GMOS at the Gemini North Telescope. Typical emission lines are identified, such as [O I], H{\alpha}, [Ca II], among others. Some species' line profiles show broad and narrow components, indicating two ejecta velocities and an asymmetric ejecta. We infer the progenitor mass of SN 2023ixf by comparing with synthetic spectra and by measuring the forbidden oxygen doublet flux. Results. Based on the flux ratio and the direct comparison with spectra models, the progenitor star of SN 2023ixf had a M_{ZAMS} between 12 and 15 M{_\odot}. In comparison with this, we find the use of the [O I] doublet flux to be less constraining of the progenitor mass. Our results agree with those from hydrodynamical modelling of the early light curve and pre-explosion image estimates pointing to a relatively low-mass progenitor.