On the Inside of Massive Galaxies: The Sloan Lens ACS Survey and Combining Gravitational Lensing with Stellar Dynamics and Stellar Population Analysis

Our understanding of the structure and formation of early-type galaxies (ETGs) is rapidly evolving, but our inability to disentangle stellar mass from dark matter often prevents direct comparison of galaxy formation models with observations without making strong assumptions, such as for the initial mass function (IMF) or dark matter mass fraction and density profile. As an example, the increase in mass-to-light ratio (M/L) along the Fundamental Plane could be partly due to changes in the structure of the ETGs, but also to a change in the ratio of dark versus stellar mass and even to a change in the stellar M/L with galaxy velocity dispersion (by a steepening of the IMF). We report on ongoing efforts to disentangle the structure of early-type galaxies using gravitational lensing, two-dimensional kinematics and stellar population analysis making use of high-resolution images from HST, integral field spectroscopy from VIMOS, and UVB/VIS spectra from X-shooter.