A feather on the hat: Tracing the giant stellar stream around the Sombrero galaxy

TL;DR

This study uses deep imaging and modeling to trace a stellar stream around the Sombrero galaxy, linking it to a recent minor event and providing insights into the galaxy's merger history.

Contribution

It presents the first full mapping of the stellar stream in M104 and models its formation, distinguishing it from the major merger event.

Findings

The tidal stream is fully characterized and is the only coherent substructure in the inner halo.

The major merger occurred over 3.5 billion years ago, with the stream forming within the last 3 billion years.

The stream's formation is independent of the earlier major merger event.

Abstract

Recent evidence of extremely metal-rich stars found in the Sombrero galaxy (M104) halo suggests that this galaxy has undergone a recent major merger with a relatively massive galaxy. In this paper, we present wide-field deep images of the M104 outskirts obtained with a 18-cm amateur telescope with the purpose of detecting any coherent tidal features from this possible major merger. Our new data, together with a model of the M104 inner halo and scattered light from stars around the field, allow us to trace for the first time the full path of the stream on both sides of the disk of the galaxy. We fully characterize the ring-like tidal structure and we confirm that this is the only observable coherent substructure in the inner halo region. This result is in agreement with the hypothesis that M104 was created by a wet major merger more than 3.5 Gyr ago that heated up the stellar population, blurring all old substructure. We generated a set of numerical models that reproduce the formation of the observed tidal structure. Our best fit model suggests the formation of this stream in the last 3 Gyr is independent of the wet major merger that created the M104 system. Therefore, the formation of the tidal stream can put a constraint on the time when the major merger occurred.