Measuring the Evolution of the M/L Ratio from the Fundamental Plane

The Fundamental plane provides a sensitive tool to measure the change in the M/L ratio of early type galaxies with redshift. The evolution of the M/L ratio is a function of the star formation history. It depends on the IMF, the formation redshift, and cosmology. Some model examples are shown, and a first result on the cluster Abell 665 at z=0.18 is given. The measurements confirm the cosmological surface brightness dimming, and imply an evolution of the (red) L/M ratio ∝ (1 + z)^1.8±0.7. More data are needed to extend this result to higher redshifts, and to test the underlying assumptions. This revised version was published online in July 2006 with corrections to the Cover Date.