Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-08-03
Astronomy and Astrophysics
Astrophysics
7 pages, 6 figures, submitted to MNRAS on August 3, 1999
Scientific paper
10.1046/j.1365-8711.2000.03311.x
Possible orbital histories of the Sgr dwarf galaxy are explored. A special-purpose N-body code is used to construct the first models of the Milky Way - Sgr Dwarf system in which both the Milky Way and the Sgr Dwarf are represented by full N-body systems and followed for a Hubble time. These models are used to calibrate a semi-analytic model of the Dwarf's orbit that enable us to explore a wider parameter space than is accessible to the N-body models. We conclude that the extant data on the Dwarf are compatible with a wide range of orbital histories. At one extreme the Dwarf initially possesses 10^{11} Solar Mass and starts from a Galactocentric distance 200 kpc. At the other extreme the Dwarf starts with 10^9 Solar Mass and Galactocentric distance 60 kpc, similar to its present apocentric distance. In all cases the Dwarf is initially dark-matter dominated and the current velocity dispersion of the Dwarf's dark matter is tightly constrained to be 21 km/s. This number is probably compatible with the smaller measured dispersion of the Dwarf's stars because of (a) the dynamical difference between dark and luminous matter, and (b) velocity anisotropy.
Binney James
Jiang Ing-Guey
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