2010/08/31 by Gregory D. Martinez, Quinn E. Minor, James Bullock +4 · 97 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Dark matter #Dark matter halo #Dwarf galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Milky Way #Physics #Radial velocity #Satellite galaxy #Solar mass #Stars #Stellar density #Stellar, planetary, and galactic studies #Velocity dispersion #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/738/1/55
published in The Astrophysical Journal 738(1), 55 (IOP Publishing) · 15 pages, 19 figures
openalex publication_date 2011/08/11 · arxiv created 2011/08/16 · arxiv updated 2011/08/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We introduce a comprehensive analysis of multi-epoch stellar line-of-sight velocities to determine the intrinsic velocity dispersion of the ultrafaint satellites of the Milky Way. Our method includes a simultaneous Bayesian analysis of both membership probabilities and the contribution of binary orbital motion to the observed velocity dispersion within a 14-parameter likelihood. We apply our method to the Segue 1 dwarf galaxy and conclude that Segue 1 is a dark-matter-dominated galaxy at high probability with an intrinsic velocity dispersion of 3.7 +1.4 − 1.1 km s −1 . The dark matter halo required to produce this dispersion must have an average density of within a sphere that encloses half the galaxy's stellar luminosity. This is the highest measured density of dark matter in the Local Group. Our results show that a significant fraction of the stars in Segue 1 may be binaries with the most probable mean period close to 10 years, but also consistent with the 180 year mean period seen in the solar vicinity at about 1σ. Despite this binary population, the possibility that Segue 1 is a bound star cluster with the observed velocity dispersion arising from the orbital motion of binary stars is disfavored by the multi-epoch stellar velocity data at greater than 99% C.L. Finally, our treatment yields a projected (two-dimensional) half-light radius for the stellar profile of Segue 1 of R 1/2 = 28 +5 − 4 pc, in excellent agreement with photometric measurements.