WFC3 GRISM confirmation of the distant cluster Cl J1449+0856 at 〈z〉 = 2.00: Quiescent and star-forming galaxy populations

R. Gobat, V. Strazzullo, E. Daddi, M. Onodera, M. Carollo, A. Renzini, A. Finoguenov, A. Cimatti, C. Scarlata, N. Arimoto

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Abstract

We present deep Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) slitless spectroscopic observations of the distant cluster Cl J1449+0856. These cover a single pointing with 18 orbits of G141 spectroscopy and F140W imaging, allowing us to derive secure redshifts down to M 140 ∼ 25.5 AB and 3σ line fluxes of ∼5 × 10-18 erg s-1 cm-2. In particular, we were able to spectroscopically confirm 12 early-type galaxies (ETGs) in the field up to z ∼ 3, 6 of which are in the cluster core, which represents the first direct spectroscopic confirmation of quiescent galaxies in a z = 2 cluster environment. With 140 redshifts in a ∼6 arcmin2 field, we can trace the spatial and redshift galaxy distribution in the cluster core and background field. We find two strong peaks at z = 2.00 and z = 2.07, where only one was seen in our previously published ground-based data. Due to the spectroscopic confirmation of the cluster ETGs, we can now reevaluate the redshift of Cl J1449+0856 at z = 2.00, rather than z = 2.07, with the background overdensity being revealed to be sparse and "sheet"-like. This presents an interesting case of chance alignment of two close yet unrelated structures, each one preferentially selected by different observing strategies. With 6 quiescent or early-type spectroscopic members and 20 star-forming ones, Cl J1449+0856 is now reliably confirmed to be at z = 2.00. The identified members can now allow for a detailed study of galaxy properties in the densest environment at z = 2.

Original languageEnglish (US)
Article number9
JournalAstrophysical Journal
Volume776
Issue number1
DOIs
StatePublished - Oct 10 2013

Keywords

  • galaxies: high-redshift

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