Evolution of Low Mass Galactic Subhalos and Dependence on Concentration
  We carry out a detailed study of the orbital dynamics and structural
evolution of over 6000 subhalos in the Via Lactea II simulation, from infall to
present. By analyzing subhalos with masses down to m = 4e5 Msun, we find that
lower mass subhalos, which are not strongly affected by dynamical friction,
exhibit behaviors qualitatively different from those found previously for more
massive ones. Furthermore, there is a clear trend of subhalos that fell into
the host earlier being less concentrated. We show that the concentration at
infall characterizes various aspects of subhalo evolution. In particular, tidal
effects truncate the growth of less concentrated subhalos at larger distances
from the host; subhalos with smaller concentrations have larger infall radii.
The concentration at infall is further shown to be a determining factor for the
subsequent mass loss of subhalos within the host, and also for the evolution of
their internal structure in the v_max-r_max plane. Our findings raise the
prospects of using the concentration to predict the tidal evolution of
subhalos, which will be useful for obtaining analytic models of galaxy
formation, as well as for near field cosmology.
