The Sizes of Early-Type Galaxies

In this letter we present a study of the size luminosity relation of 475early-type galaxies in the Virgo Cluster with Sloan Digital Sky Survey imagingdata. The analysis of our homogeneous, model-independent data set reveals thatgiant and dwarf early-type galaxies do not form one common sequence in thisrelation. The dwarfs seem to show weak or no dependence on luminosity, and donot fall on the extension of the rather steep relation of the giants. Under theassumption that the light profile shape varies continuously with magnitude, acurved relation of size and magnitude would be expected. While the galaxies doroughly follow this trend overall, we find that the dwarf galaxies aresignificantly larger and the low-luminosity giants are significantly smallerthan what is predicted. We come to the conclusion that in this scaling relationthere is not one common sequence from dwarfs to giants, but a dichotomy whichcan not be resolved by varying profile shapes. The comparison of our data to asemi-analytic model supports the idea of a physical origin of this dichotomy.Comment: Accepted by ApJL; 5 page, 3 figure