  Recent low-redshift observations have attempted to determine the star
formation histories of elliptical galaxies by tracking correlations between the
stellar population parameters (age and metallicity) and the structural
parameters that enter the fundamental plane (size and velocity dispersion).
These studies have found that velocity dispersion, rather than effective radius
or dynamical mass, is the main predictor of a galaxy's stellar age and
metallicity. In this work, we apply an analytic model that predicts the
structural properties of remnants formed in major mergers to progenitor disk
galaxies with properties taken from two different semi-analytic models. We
predict the effective radius, velocity dispersion, luminosity, age, and
metallicity of the merger remnants, enabling us to compare directly to
observations of early-type galaxies. While we find a tight correlation between
age and velocity dispersion, we find a stronger dependence of age and
metallicity on effective radius than observations report. The correlations
arise as a result of the dependence of gas fraction, age, and metallicity on
the stellar mass in the progenitor disk galaxies. These dependences induce a
rotation in the radius-velocity plane between the correlations with effective
radius and circular velocity in the disk galaxy progenitors, and the
correlations with effective radius and velocity dispersion in the elliptical
galaxy remnants. The differences between our results and those from
observations suggest that major mergers alone cannot produce the observed lack
of correlation between effective radius and stellar population parameters.
Simulations have suggested that subsequent minor mergers introduce scatter in
the effective radius while leaving the velocity dispersion essentially
unchanged. Incorporating such minor mergers into the model may, then, bring the
simulations into closer agreement with observations.
