Dwarf Satellite Galaxies
(Heidelberg 1992 - present)
- The motion of the Magellanic Clouds. Data in the
recently completed proper-motion catalogue for the southern hemisphere
as well as Hipparcos proper motion data allowed the measurement of the
proper motion of the Large and Small Magellanic Clouds to an
unprecedented accuracy and precision.
(Kroupa, Roeser & Bastian 1994;
Kroupa & Bastian 1997a;
Kroupa &
Bastian 1997c) .
- dSph satellite galaxies. Using the particle-mesh
code with sub-grids, SUPERBOX (Fellhauer, Kroupa,
Baumgart, et al., 1999, submitted), the dynamics of a
group of galaxies can be computed very efficiently on commercially
available computers. Using SUPERBOX, I am investigating tidal shaping
of low-mass satellite galaxies.
- The results indicate that the high ratios
inferred for some dSph galaxies may be accounted for by the
influence of Galactic tides on their structure and kinematics
(Kroupa
1997; Klessen
& Kroupa 1998), rather than them being dark matter
dominated.
- This conclusion became possible because this problem was studied
for the first time using more than
particles, thereby ensuring that the remnants retain a sufficient
number of particles to allow deductions that are not completely
swamped through artificial relaxation. The results suggest that the
long-lived remnants have significantly anisotropic velocity
dispersions, are non-spherical and not in virial equilibrium, but more
work is necessary to understand the exact nature of these objects.
- A major parameter study (initial satellite mass, its initial
radius, its initial position and velocity vectors, mass and extend of
Milky Way dark halo) is nearing completion. Presently about 13GB of
data have accumulated based on about 1CPU yr of computations
(Kroupa 1998f). The study will allow important
insights into the birth configuration of dSph satellites without dark
matter, if such solutions exist. They would have important
implications for the genesis of some or all dSph satellites. The most
likely implication would be that at least some of the satellites may
have been born in some past merger event
(Kroupa 1998e), which is supported by
their alignment in one or two circum-Galactic planes.
It is important to stress that even if none of the local dSph
satellites is such an object, these remnants are
nevertheless novel stellar-dynamical objects that merit further
study. Since disruption by tides is a process that must have
occurred many times, the results of this work are at least a
prediction of a class of object that must
exist but may not have been knowingly identified so far (unless
some of the local dSph satellites are examples).
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