The Fundamental Plane of Cluster Elliptical Galaxies

Using deep Hubble Space Telescope Advanced Camera for Surveys imaging and Very Large Telescope FOcal Reducer/low dispersion Spectrograph 2 spectra, we determined the velocity dispersions, effective radii, and surface brightnesses for four early-type galaxies in the cluster RDCS 1252.9 2927. All four galaxies are massive, z p 1.237 greater than . These four galaxies, combined with three from RDCS 0848 4453 at , establish the 11 10 M z p 1.276 , fundamental plane of massive early-type cluster galaxies at . The offset of the fundamental plane shows that z̄ p 1.25 the luminosity evolution in rest-frame B is for galaxies with . To 11.5 D ln (M/L ) p ( 0.98 0.06)z M 1 10 M B , reproduce the observed mass-to-light ratio ( ) evolution, we determine the characteristic age of the stars in these M/L galaxies to be Gyr; i.e., . Including selection effects caused by morphological bias 11.5 0.3 0.5 M 1 10 M 3.0 z p 3.4 , 0.3 ∗ 0.4 (the “progenitor bias”), we estimate an age of Gyr, or for the elliptical galaxy population. Massive 0.2 0.2 2.1 z p 2.3 0.2 ∗ 0.2 cluster early-type galaxies appear to have a large fraction of stars that formed early in the history of the universe. However, there is a large scatter in the derived values, which is confirmed by the spread in the galaxies’ colors. M/L Two lower mass galaxies in our sample have much lower values, implying significant star formation z̄ p 1.25 M/L close to the epoch of observation. Thus, even in the centers of massive clusters, there appears to have been significant star formation in some massive, , galaxies at . 11 M 10 M z 1.5 , Subject headings: galaxies: clusters: general — galaxies: clusters: individual (RDCS 1252.9 2927) — galaxies: elliptical and lenticular, cD — galaxies: evolution — galaxies: fundamental parameters — galaxies: photometry