Stellar proper motions in the outskirts of classical dwarf spheroidal galaxies with Gaia EDR3

TL;DR

This study uses Gaia EDR3 data to identify and analyze stars beyond the nominal limits of six classical dwarf spheroidal galaxies, exploring their potential extended halos or tidal debris.

Contribution

It provides the first systematic identification of candidate extra-tidal stars in multiple dwarf spheroidals using Gaia EDR3 astrometry and radial velocities.

Findings

Detected candidate stars beyond the King radius with high probability.

Some candidates align with the orbital tracks of the galaxies.

Potential evidence for extended stellar halos or tidal debris.

Abstract

We use Gaia EDR3 data to identify stars associated with six classical dwarf spheroidals (Draco, Ursa Minor, Sextans, Sculptor, Fornax, Carina) at their outermost radii, beyond their nominal King stellar limiting radius. For all of the dSphs examined, we find radial velocity matches with stars residing beyond the King limiting radius and with $> 50\%$ astrometric probability (four in Draco, two in Ursa Minor, eight in Sextans, two in Sculptor, twelve in Fornax, and five in Carina), indicating that these stars are associated with their respective dwarf spheroidals (dSphs) at high probability. We compare the positions of our candidate "extra-tidal" stars with the orbital tracks of the galaxies, and identify stars, both with and without radial velocity matches, that are consistent with lying along the orbital track of the satellites. However, given the small number of candidate stars, we cannot make any conclusive statements about the significance of these spatially correlated stars. Cross matching with publicly available catalogs of RR Lyrae, we find one RR Lyrae candidate with $> 50\%$ astrometric probability outside the limiting radius in each of Sculptor and Fornax, two such candidates in Draco, nine in Ursa Minor, seven in Sextans, and zero in Carina. Follow-up spectra on all of our candidates, including possible metallicity information, will help confirm association with their respective dSphs, and could represent evidence for extended stellar halos or tidal debris around these classical dSphs.