We have obtained radial velocities of three K giants and one faint carbon star in LGS 3, a dwarf companion of M31, based on 12 individual spectra obtained with the HIRES spectrograph on the Keck I telescope. The mean precision of these measurements is 3.8 km s-1. The mean systemic velocity of LGS 3 is -282.2 ± 3.5 km s-1. Monte Carlo simulations that take into account the individual velocity uncertainties and the maximum observed velocity difference reveal that the central velocity dispersion of LGS 3 is in the range 2.6-30.5 km s-1, with 95% confidence; the most likely value for the central dispersion is 7.9+5.3-2.9 km s-1. These results agree with the kinematics of H I gas in LGS 3. This contrasts with the tendency for the gas and stars in other low-luminosity Local Group dwarfs to exhibit distinct spatial and kinematic properties. Taking into account the relative youth of LGS 3, we conclude that the " asymptotic " M/L ratio - the value the galaxy would exhibit if it were composed only of ancient stars - is M/Lv,LGS3 ≥ 11 (at a 97.5% confidence level), with a most probable value of 95+175-56. These values are consistent with the M/Lv ratios observed in other well-studied early-type dwarfs of the Local Group. We have also estimated the mass of LGS 3 using modified Newtonian dynamics. These data represent the first moderately high precision optical spectra of giants in a dwarf system beyond the Galactic halo. We suggest future studies that are now feasible to study the dynamics of dwarf galaxies throughout the Local Group and beyond.
|Original language||English (US)|
|Number of pages||7|
|Journal||Publications of the Astronomical Society of the Pacific|
|State||Published - Mar 1999|
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science