An effective Thermodynamic Description of Galactic Haloes
  The observation of flat rotation curves in asymptotic region of galaxies
implies that the dark matter density profile decreases exponentially with the
gravitational potential in this region. It is curious that this behavior is
identical to what one would have from a Boltzmann gas in thermal equilibrium.
This suggests that an {\it effective} Boltzmann gas description of dark matter
is possible for the halo, which follows even though no requirement of thermal
equilibrium is assumed for the dark matter particles. We examine some
qualitative and quantitative consequences of such an effective description.
This is done by studying a simple model that takes into account gravitational
self-interactions of dark matter and its gravitational interactions with the
baryonic core.
  Solutions to the dynamics are determined by two parameters, one of which is
the ratio of the dark matter mass to the effective temperature of the gas.
Crude estimates can be made for these parameters based on observations.
