111 research outputs found
Warps and Cosmic Infall
N-body simulations show that when infall reorientates the outer parts of a
galactic halo by several degrees per Gyr, a self-gravitating disk that is
embedded in the halo develops an integral-sign warp that is comparable in
amplitude to observed warps. Studies of angular-momentum acquisition suggest
that the required rate of halo reorientation is realistic for galaxies like the
Milky Way.Comment: 4 pages, 2 figures, submitted to MNRAS on June 19, 199
The Orbit and Mass of the Sagittarius Dwarf Galaxy
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.Comment: 7 pages, 6 figures, submitted to MNRAS on August 3, 199
Orbital Evolution of Scattered Planets
A simple dynamical model is employed to study the possible orbital evolution
of scattered planets and phase plane analysis is used to classify the parameter
space and solutions. Our results reconfirm that there is always an increase in
eccentricity when the planet was scattered to migrate outward when the initial
eccentricity is zero. Applying our study on the Solar System and considering
the existence of the Kuiper Belt, this conclusion implies that Neptune was
dynamically coupled with the Kuiper Belt in the early phase of the Solar
System, which is consistent with the simulational model in Thommes, Duncan &
Levison (1999).Comment: AAS Latex file, 21 pages, accepted by Ap
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