On the orbital and internal evolution of cluster galaxies
  Galaxies inhabiting a cluster environment experience significant evolution in
their orbital motions throughout time; this is accompanied by changes in the
anisotropy parameter, measuring the relative importance of radial and
tangential motions for a given class of objects. Along with orbital changes,
galaxies in clusters are well known to undergo severe alteration in their
hot/cold gas content and star formation properties. Understanding the link
between the changes in the internal properties of galaxies and their orbital
motion is of crucial importance in the study of galaxy evolution, as it could
unveil the primary mechanism responsible for its environmental dependence. Do
the changes in the internal properties happen in parallel with those in the
orbital motion? Or are the orbital features at the time of infall what
determines the fate of the member galaxies? Alternatively: are the properties
of galaxies at a given time related to the coeval orbital anisotropy or are
they better related to the anisotropy at infall? In order to answer these
questions, we studied the orbital evolution of different galaxy populations in
the semi-analytic models of Guo et al. (2011) applied on to the Millennium
Simulation. For each class of objects, characterised by different internal
properties (such as age, star formation rate and colour), we studied the
anisotropy profile at redshift zero and its evolution by tracing the
progenitors back in time. We conclude that the orbital properties at infall
strongly influence the subsequent evolution of the internal features of
galaxies and that the overall anisotropy of the galaxy population tends to
increase with time.
