16,801 research outputs found
Dynamical friction in dwarf galaxies
We present a simplified analytic approach to the problem of the spiraling of
a massive body orbiting within the dark halo of a dwarf galaxy. This dark halo
is treated as the core region of a King distribution of dark matter particles,
in consistency with the observational result of dwarf galaxies having solid
body rotation curves. Thus we derive a simple formula which provides a reliable
and general first order solution to the problem, totally analogous to the one
corresponding to the dynamical friction problem in an isothermal halo. This
analytic approach allows a clear handling and a transparent understanding of
the physics and the scaling of the problem. A comparison with the isothermal
case shows that in the core regions of a King sphere, dynamical friction
proceeds at a different rate, and is sensitive to the total core radius. Thus,
in principle, observable consequences may result. In order to illustrate the
possible effects, we apply this formula to the spiraling of globular cluster
orbits in dwarf galaxies, and show how present day globular cluster systems
could in principle be used to derive better limits on the structure of dark
halos around dwarf galaxies, when the observational situation improves. As a
second application, we study the way a massive black hole population forming a
fraction of these dark halos would gradually concentrate towards the centre,
with the consequent deformation of an originally solid body rotation curve.
This effect allows us to set limits on the fraction/mass of any massive black
hole minority component of the dark halos of dwarf galaxies. In essence, we
take advantage of the way the global matter distribution fixes the local
distribution function for the dark matter particles, which in turn determines
the dynamical friction problem.Comment: 8 pages, 1 figure, Accepted in MNRA
A Dimensional study of Disk Galaxies
We present a highly simplified model of the dynamical structure of a disk
galaxy where only two parameters fully determine the solution, mass and angular
momentum. We show through simple physical scalings that once the mass has been
fixed, the angular momentum parameter is expected to regulate such
critical galactic disk properties as colour, thickness of the disk and disk to
bulge ratio. It is hence expected to be the determinant physical ingredient
resulting in a given Hubble type. A simple analytic estimate of for
an observed system is provided. An explicit comparison of the distribution of
several galactic parameters against both Hubble type and is performed
using observed galaxies. Both such distributions exhibit highly similar
characteristics for all galactic properties studied, suggesting as a
physically motivated classification parameter for disk galaxies.Comment: 10 pages including 11 figures, Final version, MNRAS in pres
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