Luminosity functions of elliptical galaxies at z<1.2

The luminosity functions of E/SO galaxies are constructed in three different redshift bins (0.2 < z < 0.55, 0.55 < z < 0.8, 0.8 < z < 1.2), using the data from the Hobble Space Telescope (HST) Medium Deep Survey and other HST surveys. These independent luminosity functions show the brightening in the luminosity of E/SOs by about 0.5-1 mag at z similar to 1 and no sign of significant number evolution. This is the first direct measurement of the luminosity evolution of E/SO galaxies, and our results support the hypothesis of a high redshift of formation (z > 1) for elliptical galaxies, together with weak evolution of the major merger rate at z < 1.