Structural analysis of the Sextans dwarf spheroidal galaxy

TL;DR

This study provides a detailed analysis of the Sextans dwarf spheroidal galaxy, revealing its stellar substructure and suggesting it is not currently undergoing significant tidal disruption, based on wide-field photometry and statistical analysis.

Contribution

It offers the first wide-field photometric analysis of Sextans' substructure and assesses its gravitational binding status and tidal interaction with the Milky Way.

Findings

Detected multiple stellar over-densities around Sextans.

Found the substructures are gravitationally bound and not tidal tails.

Supported a low-eccentricity orbit for Sextans.

Abstract

We present wide-field $g$ and $i$ band stellar photometry of the Sextans dwarf spheroidal galaxy and its surrounding area out to four times its half-light radius ($r_h=695\,$pc), based on images obtained with the Dark Energy Camera at the 4-m Blanco telescope at CTIO. We find clear evidence of stellar substructure associated with the galaxy, extending to a distance of $82\arcmin$ (2\,kpc) from its centre. We perform a statistical analysis of the over-densities and find three distinct features, as well as an extended halo-like structure, to be significant at the $99.7\%$ confidence level or higher. Unlike the extremely elongated and extended substructures surrounding the Hercules dwarf spheroidal galaxy, the over-densities seen around Sextans are distributed evenly about its centre, and do not appear to form noticeable tidal tails. Fitting a King model to the radial distribution of Sextans stars yields a tidal radius $r_t =83.2\arcmin\pm7.1\arcmin$ (2.08$\pm$0.18\,kpc), which implies the majority of detected substructure is gravitationally bound to the galaxy. This finding suggests that Sextans is not undergoing significant tidal disruption from the Milky Way, supporting the scenario in which the orbit of Sextans has a low eccentricity.