The Role of Dissipation in the Scaling Relations of Cosmological Merger
  Remnants
  There are strong correlations between the three structural properties of
elliptical galaxies -- stellar mass, velocity dispersion and size -- in the
form of a tight "fundamental plane" and a "scaling relation" between each pair.
Major mergers of disk galaxies are assumed to be a mechanism for producing
ellipticals, but semi-analytic galaxy formation models (SAM) have encountered
apparent difficulties in reproducing the observed slope and scatter of the
size-mass relation. We study the scaling relations of merger remnants using
progenitor properties from two SAMs. We apply a simple merger model that
includes gas dissipation and star formation based on theoretical considerations
and simulations. Combining the SAMs and the merger model allows calculation of
the structural properties of the remnants of major mergers that enter the
population of elliptical galaxies at a given redshift. Without tuning the
merger model parameters for each SAM, the results roughly match the slope and
scatter in the observed scaling relations and their evolution in the redshift
range $z=0-3$. Within this model, the observed scaling relations, including the
tilt of the fundamental plane relative to the virial plane, result primarily
from the decrease of gas fraction with increasing progenitor mass. The scatter
in the size-mass relation of the remnants is reduced from that of the
progenitors because of a correlation between progenitor size and gas fraction
at a given mass.
