Cosmic Evolution of Virial and Stellar Mass in Massive Early-Type
  Galaxies
  We measure the average mass properties of a sample of 41 strong gravitational
lenses at moderate redshift (z ~ 0.4 - 0.9), and present the lens redshift for
6 of these galaxies for the first time. Using the techniques of strong and weak
gravitational lensing on archival data obtained from the Hubble Space
Telescope, we determine that the average mass overdensity profile of the lenses
can be fit with a power-law profile (Delta_Sigma prop. to R^{-0.86 +/- 0.16})
that is within 1-sigma of an isothermal profile (Delta_Sigma prop. to R^{-1})
with velocity dispersion sigma_v = 260 +/- 20 km/s. Additionally, we use a
two-component de Vaucouleurs+NFW model to disentangle the total mass profile
into separate luminous and dark matter components, and determine the relative
fraction of each component. We measure the average rest frame V-band stellar
mass-to-light ratio (Upsilon_V = 4.0 +/- 0.6 h M_sol/L_sol) and virial
mass-to-light ratio (tau_V = 300 +/- 90 h M_sol/L_sol) for our sample,
resulting in a virial-to-stellar mass ratio of M_vir/M_* = 75 +/- 25. Finally,
we compare our results to a previous study using low redshift lenses, to
understand how galaxy mass profiles evolve over time. We investigate the
evolution of M_vir/M_*(z) = alpha(1+z)^{beta}, and find best fit parameters of
alpha = 51 +/- 36 and beta = 0.9 +/- 1.8, constraining the growth of virial to
stellar mass ratio over the last ~7 Gigayears. We note that, by using a sample
of strong lenses, we are able to constrain the growth of M_vir/M_*(z) without
making any assumptions about the IMF of the stellar population.
