Type Ia supernovae in globular clusters: observational upper limits

TL;DR

This study searches for globular clusters at the locations of type Ia supernovae using archival HST data, setting upper limits on their occurrence in such clusters and constraining models of supernova progenitors in dense stellar environments.

Contribution

It provides the first observational upper limits on the fraction of type Ia supernovae occurring in globular clusters, using a comprehensive archival data analysis.

Findings

No globular clusters detected at supernova positions.

Upper limit of 0.09 on supernovae in globular clusters for the full sample.

Constraints on enhancement factors for supernova progenitors in dense environments.

Abstract

In the dense stellar environment of the globular clusters, compact binaries are produced dynamically. Therefore the fraction of type Ia supernovae that explode in globular clusters is expected to be higher than the fraction of mass residing in these. We have searched for globular clusters at the positions of observed type Ia supernovae. We used archival HST images and literature data, covering the positions either before the supernovae exploded, or long enough after that the supernovae have faded below the luminosities of globular clusters. We did not find evidence for globular clusters at any of the supernova positions. For 18 type Ia supernovae, the observations are sensitive enough that any globular cluster would have been detected, and for further 17 type Ia supernovae, the brighter globular clusters would have been detected. Correcting for incompleteness, we derive a 90% upper limit of 0.09 on the fraction of type Ia supernovae that explode in globular clusters for the full sample and 0.22 for the sample of supernovae in late-type galaxies. This allows us to limit enhancements per unit stellar mass for a coeval population eta_{co}<50 (100) with 90% (99%) confidence. We find that by observing the positions of a sample of less than 100 type Ia supernovae in the outer parts of early-type galaxies, it will be possible to probe the currently favoured range of eta_{co}~1-10.