Zooming In on the Progenitors of Superluminous Supernovae With the HST

TL;DR

This study uses HST ultraviolet imaging to analyze the host galaxies of hydrogen-poor superluminous supernovae, revealing their irregular, compact nature and suggesting they form in dense, star-forming environments, with progenitors possibly differing from those of LGRBs.

Contribution

First detailed HST UV imaging of SLSN host galaxies, characterizing their morphology, star formation, and SN locations to understand progenitor environments.

Findings

Host galaxies are irregular, compact dwarf galaxies with median radius 0.9 kpc.

SLSNe occur in high star formation density regions, indicating dense environments.

SN locations are intermediate in clustering between LGRBs and normal SNe.

Abstract

We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including 11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the superb angular resolution of HST, we characterize the galaxies' morphological properties, sizes and star formation rate (SFR) densities. We determine the supernova (SN) locations within the host galaxies through precise astrometric matching, and measure physical and host-normalized offsets, as well as the SN positions within the cumulative distribution of UV light pixel brightness. We find that the host galaxies of H-poor SLSNe are irregular, compact dwarf galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR densities are high (<Sigma_SFR> ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe form in overdense environments. Their locations trace the UV light of their host galaxies, with a distribution intermediate between that of long-duration gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions of their hosts) and a uniform distribution (characteristic of normal core-collapse SNe), though cannot be statistically distinguished from either with the current sample size. Taken together, this strengthens the picture that SLSN progenitors require different conditions than those of ordinary core-collapse SNe to form, and that they explode in broadly similar galaxies as do LGRBs. If the tendency for SLSNe to be less clustered on the brightest regions than are LGRBs is confirmed by a larger sample, this would indicate a different, potentially lower-mass progenitor for SLSNe than LRGBs.