RXJ0848.6+4453: The Evolution of Galaxy Sizes and Stellar Populations in a z=1.27 Cluster

Abstract

RXJ0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of galaxies. Our analysis of stellar populations and star formation history in the cluster covers 24 members and is based on deep optical spectroscopy from Gemini North and imaging data from HST. Focusing on the 13 bulge-dominated galaxies for which we can determine central velocity dispersions, we find that these show a smaller evolution of sizes and velocity dispersions than reported for field galaxies and galaxies in poorer clusters. The galaxies in RXJ0848.6+4453 populate the Fundamental Plane similar to that found for lower redshift clusters with a zero point offset corresponding to an epoch of last star formation at z_form= 1.95+-0.2. The spectra of the galaxies in RXJ0848.6+4453 are dominated by young stellar populations at all galaxy masses and in many cases show emission indicating low level on-going star formation. The average age of the young stellar populations (estimated from H-zeta) is consistent with a major star formation episode 1-2 Gyr prior, which in turn agrees with z_form=1.95. Galaxies dominated by young stellar populations are distributed throughout the cluster. We speculate that low level star formation has not yet been fully quenched in the center of this cluster may be because the cluster is significantly poorer than other clusters previously studied at similar redshifts, which appear to have very little on-going star formation in their centers.

Accepted for publication in Astronomical Journal. High-resolution figures available from the first author by request

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• Galaxy populations in massive z=0.2-0.9 clusters: I. Analysis of spectroscopy
• Morphological evolution in situ: Disk-dominated cluster red sequences at z ~ 1.25
• Molecular Gas Reservoirs in Massive Quiescent Galaxies at $\mathrm{z}\sim 0.7$ Linked to Late Time Star Formation
• Stellar population properties of individual massive early-type galaxies at 1.4 < z < 2
• Age, metallicity and star formation history of spheroidal galaxies in cluster at z~1.2
• The Fundamental Plane of cluster spheroidal galaxies at z$\sim 1.3$. Evidence for mass-dependent evolution
• The most massive galaxies in clusters are already fully grown at $z\sim 0.5$
• The Evolution of Bulge-Dominated Field Galaxies from z~1 to the Present