The Draco Dwarf Spheroidal Galaxy in the First Year of DESI Data
Abstract
We investigate the spatial distribution, kinematics, and metallicity of stars in the Draco dwarf spheroidal galaxy using data from the Dark Energy Spectroscopic Instrument (DESI). We identify 155 high probability members of Draco using line of sight velocity and metallicity information derived from DESI spectroscopy along with {\it Gaia} DR3 proper motions. We find a mean line of sight velocity of km s with dispersion = km s and mean metallicity = , consistent with previous results. We also find that Draco has a steep metallicity gradient within the half-light radius, and a metallicity gradient that flattens beyond the half-light radius. We identify eight high probability members outside the King tidal radius, four of which we identify for the first time. These extra-tidal stars are not preferentially aligned along the orbit of Draco. We compute an average surface brightness of 34.02 mag within an elliptical annulus from the King tidal radius of 48.1 arcmin to 81 arcmin.
Keywords
Cite
@article{arxiv.2509.21822,
title = {The Draco Dwarf Spheroidal Galaxy in the First Year of DESI Data},
author = {J. Ding and C. Rockosi and Ting S. Li and S. E. Koposov and A. H. Riley and W. Wang and A. P. Cooper and N. Kizhuprakkat and M. Lambert and G. E. Medina and N. Sandford and J. Aguilar and S. Ahlen and D. Bianchi and D. Brooks and T. Claybaugh and A. de la Macorra and P. Doel and J. E. Forero-Romero and E. Gaztanaga and S. Gontcho A Gontcho and G. Gutierrez and J. Guy and M. Ishak and R. Kehoe and T. Kisner and A. Kremin and O. Lahav and M. Landriau and L. Le Guillou and A. Meisner and R. Miquel and J. Moustakas and F. Prada and I. Perez-Rafols and G. Rossi and E. Sanchez and M. Schubnell and J. Silber and D. Sprayberry and G. Tarle and B. A. Weaver and R. Zhou},
journal= {arXiv preprint arXiv:2509.21822},
year = {2025}
}