Extended stellar substructure surrounding the Bo\"otes I dwarf spheroidal galaxy

TL;DR

This study uses deep photometry to reveal extended stellar substructure and signs of tidal disruption around the Bo"otes I dwarf galaxy, challenging existing models of its dynamics.

Contribution

It provides new observational evidence of stellar substructure and tidal features around Bo"otes I, prompting a review of theoretical models.

Findings

Detection of large, extended stellar substructure.

Identification of a break radius indicating extra-tidal stars.

Evidence of ongoing tidal disruption.

Abstract

We present deep stellar photometry of the Bo\"otes I dwarf spheroidal galaxy in g and i band filters, taken with the Dark Energy Camera at Cerro Tololo in Chile. Our analysis reveals a large, extended region of stellar substructure surrounding the dwarf, as well as a distinct over-density encroaching on its tidal radius. A radial profile of the Bo\"otes I stellar distribution shows a break radius indicating the presence of extra-tidal stars. These observations strongly suggest that Bo\"otes I is experiencing tidal disruption, although not as extreme as that exhibited by the Hercules dwarf spheroidal. Combined with revised velocity dispersion measurements from the literature, we see evidence suggesting the need to review previous theoretical models of the Bo\"otes I dwarf spheroidal galaxy.