  In this paper we study aspects of the ergodic theory of the geodesic flow on
a non-compact negatively curved manifold. It is a well known fact that every
continuous potential on a compact metric space has a maximizing measure.
Unfortunately, for non-compact spaces this fact is not longer true. For the
geodesic flow we provide a criterion that ensures the existence of a maximizing
measure for uniformly continuous potentials. We prove that the only obstruction
to the existence of a maximizing measure is the full escape of mass phenomenon.
To the best of our knowledge, this is the first general result on the existence
of maximizing measures for non-compact topological spaces which does not
require the potential to be coercive. We study zero temperature limits of
equilibrium measures for a suitable family of potentials. We prove some
convergence and divergence results for the limiting behaviour of such measures.
Among some consequences we obtain that the geodesic flow has the intermediate
entropy property and that equilibrium states are dense in the space of
invariant probability measures.
