* Astronomy

Title: Stellar populations and evolution of early-type cluster galaxies: Constraints from optical imaging and spectroscopy of z=0.5-0.9 galaxy clusters
Authors: Inger Jorgensen, Kristin Chiboucas (Gemini Observatory)

We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z=0.54), RXJ0152.7-1357 (z=0.83), and RXJ1226.9+3332 (z=0.89); based on high S/N ground-based optical spectroscopy and HST imaging for 17-34 members in each cluster. We find no indication of evolution of sizes or velocity dispersions with redshift at a given dynamical galaxy mass. We establish the Fundamental Plane (FP) and scaling relations between absorption line indices and velocity dispersions. We confirm the steeper FP at z=0.86 compared to the low redshift FP, indicating (under the assumption of passive evolution) the formation redshift, z_form, depends on the galaxy velocity dispersion (or mass). z_form varies from z_form=1.24±0.05 at velocity dispersion of 125 km/s to 1.95±0.25 at 225 km/s. The three clusters and the low redshift sample follow similar scaling relations between absorption line indices and velocity dispersions. The strength of the higher order Balmer lines Hdelta and Hgamma implies z_form>2.8. From the line strengths we find that [M/H] for MS0451.6-0305 is about 0.2 dex below that of the other clusters, and confirm our previous result that [alpha/Fe] for RXJ0152.7-1357 is about 0.3 dex higher than that of the other clusters. These differences between the high-redshift clusters and the low redshift sample are inconsistent with a passive evolution scenario for early-type cluster galaxies over the redshift interval studied.

Read more (2925kb, PDF)