Hubble Space Telescope observations of the host galaxies and environments of calcium-rich supernovae

TL;DR

This study uses Hubble Space Telescope imaging to investigate the host environments of calcium-rich supernovae, revealing that their large offsets are likely due to high-velocity progenitors traveling far from their origins.

Contribution

First Hubble imaging of multiple calcium-rich supernovae hosts, demonstrating the absence of underlying sources at explosion sites and supporting high-velocity progenitor models.

Findings

No underlying sources at explosion sites in all observed cases.

Large offsets are consistent with high-velocity progenitors traveling significant distances.

Lack of host systems appears to be a common feature of calcium-rich supernovae.

Abstract

Calcium-rich supernovae represent a significant challenge for our understanding of the fates of stellar systems. They are less luminous than other supernova (SN) types and they evolve more rapidly to reveal nebular spectra dominated by strong calcium lines with weak or absent signatures of other intermediate- and iron-group elements, which are seen in other SNe. Strikingly, their explosion sites also mark them out as distinct from other SN types. Their galactocentric offset distribution is strongly skewed to very large offsets (around one third are offset greater than 20 kpc), meaning they do not trace the stellar light of their hosts. Many of the suggestions to explain this extreme offset distribution have invoked the necessity for unusual formation sites such as globular clusters or dwarf satellite galaxies, which are therefore difficult to detect. Building on previous work attempting to detect host systems of nearby Ca-rich SNe, we here present Hubble Space Telescope imaging of 5 members of the class - 3 exhibiting large offsets and 2 coincident with the disk of their hosts. We find no underlying sources at the explosion sites of any of our sample. Combining with previous work, the lack of a host system now appears to be a ubiquitous feature amongst Ca-rich SNe. In this case the offset distribution is most readily explained as a signature of high-velocity progenitor systems that have travelled significant distances before exploding.