1998/07/29 by Mario Mateo, Edward W. Olszewski, Steven S. Vogt +2 · 64 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Dark galaxy #Dark matter #Dark matter halo #Dwarf galaxy #Dwarf spheroidal galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Globular cluster #Halo #Interacting galaxy #Local Group #Milky Way #Physics #Population #Stellar, planetary, and galactic studies #Velocity dispersion #astro-ph
paper · pdf · doi:10.1086/300618
published in The Astronomical Journal 116(5), 2315-2327 (Institute of Physics) · 32 pages plus 6 figs (fig 2 unavailable) plus 7 pages of tables Accepted for Astronomical Journal, Nov 1998 "MOND" section revised because it was pointed out by an alert reader that we used an out-of-date value for the MOND acceleration parameter. MOND can now plausibly account for the Leo I velocity dispersion
arxiv created 1998/07/29 · openalex publication_date 1998/11/01 · arxiv updated 2016/08/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present radial velocities of 33 red giants in the Leo I dwarf spheroidal galaxy (dSph) obtained from spectra taken with the HIRES echelle spectrograph on the Keck Telescope. These data have a mean precision of 2.2 km s -1 and lead to estimates of the central velocity dispersion and systemic velocity of Leo I of 8.8 ± 1.3 km s -1 and 287.0 ± 1.9 km s -1 , respectively. The systemic velocity confirms past results that Leo I has an unusually large galactocentric velocity, implying the presence of a massive dark halo in the Milky Way or an extended dark component pervading the Local Group. The V -band M / L ratio of Leo I is in the range 3.5–5.6. We have produced a set of models that accounts for the effects of stellar evolution on the global mass-to-light ratio of a composite population. Because Leo I contains a dominant intermediate-age population, we find that the V -band mass-to-light ratio of Leo I would be in the range 6–13 if it were composed exclusively of old stars such as those found in globular clusters. This suggests that Leo I probably does contain a significant dark halo. The mass of this halo is approximately 2 × 10 7 M ☉ , similar to the dark halo masses inferred for all other galactic dSph galaxies. Because Leo I is isolated and has passed the Milky Way at most once in the past, external tides could not plausibly have inflated its central dispersion to the observed value. We also considered whether modified Newtonian dynamics (MOND) could account for the internal kinematics of Leo I and conclude that this alternative gravitational model can account for the Leo I kinematics adequately without requiring a dark halo.