No velocity-kicks are required to explain large-distance offsets of Ca-rich supernovae and short-GRBs

TL;DR

This study explains the large offsets of Ca-rich supernovae and short-GRBs by extended stellar populations in galaxy halos, negating the need for large velocity kicks or globular cluster origins.

Contribution

It demonstrates that the large spatial offsets of these transients are due to extended stellar halos, challenging previous models requiring high velocity kicks or globular cluster environments.

Findings

Large offsets explained by extended stellar populations in galaxy halos.

No large velocity kicks or globular clusters needed for transient origins.

Offset distributions vary with galaxy type, supporting older stellar population origins.

Abstract

The environments of explosive transients link their progenitors to the underlying stellar population, providing critical clues for their origins. However, some Ca-rich supernovae (SNe) and short gamma ray burst (sGRBs) appear to be located at remote locations, far from the stellar population of their host galaxy, challenging our understanding of their origin and/or physical evolution. These findings instigated models suggesting that either large velocity kicks were imparted to their progenitors, allowing them to propagate to large distances and attain their remote locations; or that they formed in dense globular clusters residing in the halos. Here we show that instead, the large spatial-offsets of these transients are naturally explained by the observations of highly extended underlying stellar populations in (mostly early type) galaxy halos, typically missed since they can only be identified through ultra-deep/stacked images. Consequently, no large velocity kicks, nor halo globular cluster environments are required in order to explain the origin of these transients. These findings support thermonuclear explosions on white-dwarfs, for the origins of Ca-rich SNe progenitors, and no/small-natal-kicks given to sGRB progenitors. Since early-type galaxies contain older stellar populations, transient arising from older stellar populations would have larger fractions of early-type galaxy hosts, and consequently larger fractions of transients at large offsets. This is verified by our results for sGRBs and Ca-rich SNe showing different offset distributions in early vs. late-type galaxies. Furthermore, once divided between early and late type galaxies, the offsets' distributions of the different transients are consistent with each other. Finally, we point out that studies of other transients' offset distribution (e.g. Ia-SNe or FRBs) should similarly consider the host galaxy-type.