Size Evolution of Early-Type Galaxies and Massive Compact Objects as the
  Dark Matter
  The dramatic size evolution of early-type galaxies from z ~ 2 to 0 poses a
new challenge in the theory of galaxy formation, which may not be explained by
the standard picture. It is shown here that the size evolution can be explained
if the non-baryonic cold dark matter is composed of compact objects having a
mass scale of ~10^5 M_sun. This form of dark matter is consistent with or only
weakly constrained by the currently available observations. The kinetic energy
of the dark compact objects is transferred to stars by dynamical friction, and
stars around the effective radius are pushed out to larger radii, resulting in
a pure size evolution. This scenario has several good properties to explain the
observations, including the ubiquitous nature of size evolution and faster
disappearance of higher density galaxies.
