Ages and metallicities of quiescent early-type galaxies. Filled symbols correspond to the H_βO and [MgFe]’ line-strength measured over the stacked SDSS spectra of La Barbera et al. (2013), with the color code given by the mean stellar velocity dispersion of each stack. The background model grid shows the FASTAR predictions for those two indices for a Milky Way IMF (solid lines). For reference, the grid for a bottom-heavy IMF (single power law with α = 3) is also shown with dashed lines. As expected, the prediction from the FASTAR models is that quiescent early-type galaxies become increasingly more metal-rich and older when increasing velocity dispersion. Models and data have been convolved to the resolution of the highest σ stack.