Central dark matter trends in early-type galaxies

We analyze the correlations between the central dark matter content of early-type galaxies and their sizes and ages, using a sample of intermediate-redshift (z˜ 0.2) gravitational lenses from the SLACS survey, and by comparing them to a larger sample of z˜0 galaxies. For a given stellar mass, we find that for galaxies with larger sizes, the DM fraction increases and the mean DM density decreases, consistently with the cuspy halos expected in cosmological formation scenarios. The DM fraction also decreases with stellar age, which can be partially explained by the inverse correlation between size and age. The residual trend may point to systematic dependencies on formation epoch of halo contraction or stellar initial mass functions