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arXiv · 1305.3577

Galaxy evolution in overdense environments at high redshift: passive early-type galaxies in a cluster at redshift 2

V. Strazzullo·R. Gobat·E. Daddi·M. Onodera·M. Carollo·M. Dickinson·A. Renzini·N. Arimoto·A. Cimatti·A. Finoguenov·R. -R. Chary
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Abstract

We present a study of galaxy populations in the central region of the IRAC-selected, X-ray detected galaxy cluster Cl J1449+0856 at z=2. Based on a sample of spectroscopic and photometric cluster members, we investigate stellar populations and morphological structure of cluster galaxies over an area of ~0.7Mpc^2 around the cluster core. The cluster stands out as a clear overdensity both in redshift space, and in the spatial distribution of galaxies close to the center of the extended X-ray emission. The cluster core region (r<200 kpc) shows a clearly enhanced passive fraction with respect to field levels. However, together with a population of massive passive galaxies mostly with early-type morphologies, it also hosts massive actively star-forming, often highly dust-reddened sources. Close to the cluster center, a multi-component system of passive and star-forming galaxies could be the future BCG still assembling. We observe a clear correlation between passive stellar populations and an early-type morphology, in agreement with field studies at similar redshift. Passive early-type galaxies in this clusters are typically a factor 2-3 smaller than similarly massive early-types at z~0, but also on average larger by a factor ~2 than their field analogs at z~2, lending support to recent claims of an accelerated structural evolution in high-redshift dense environments. These results point towards the early formation of a population of massive galaxies, already evolved both in their structure and stellar populations, coexisting with still-actively forming massive galaxies in the central regions of young clusters 10 billion years ago.

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V. Strazzullo, R. Gobat, E. Daddi, M. Onodera, M. Carollo, M. Dickinson, A. Renzini, N. Arimoto, A. Cimatti, A. Finoguenov, R. -R. Chary. 2013-05-15. Galaxy evolution in overdense environments at high redshift: passive early-type galaxies in a cluster at redshift 2. https://doi.org/10.1088/0004-637x/772/2/118

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