Star-forming Blue ETGs in Two Newly Discovered Galaxy Overdensities in the HUDF at z=1.84 and 1.9: Unveiling the Progenitors of Passive ETGs in Cluster Cores
Journal
Date Issued
2015
Author(s)
Mei, Simona
•
Scarlata, Claudia
•
•
Newman, Jeffrey A.
•
Weiner, Benjamin J.
•
Ashby, Matthew L. N.
•
•
Conselice, Chistopher J.
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Finkelstein, Steven L.
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Galametz, Audrey
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Grogin, Norman A.
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Koekemoer, Anton M.
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Huertas-Company, Marc
•
Lani, Caterina
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Lucas, Ray A.
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Papovich, Casey
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Rafelski, Marc
•
Teplitz, Harry I.
Description
This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program and the 3D- HST Treasury Program (GO 12177 and 12328) with the NASA/ESA HST , which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. This work is based in part on observations made with the Spitzer Space Telescope , which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. S.M. acknowledges financial support from the Institut Universitaire de France (IUF), of which she is a senior member. We thank the referee for very useful comments that improved the paper. Facilities: HST (ACS and WFC3), Spitzer (IRAC)
Abstract
We present the discovery of two galaxy overdensities in the Hubble Space Telescope UDF: a proto-cluster, HUDFJ0332.4-2746.6 at z=1.84+/- 0.01, and a group, HUDFJ0332.5-2747.3 at z=1.90 ± 0.01. Assuming viralization, the velocity dispersion of HUDFJ0332.4-2746.6 implies a mass of {{M}200}=(2.2+/- 1.8)× {{10}14} {{M}☉ }, consistent with the lack of extended X-ray emission. Neither overdensity shows evidence of a red sequence. About 50% of their members show interactions and/or disturbed morphologies, which are signatures of merger remnants or disk instability. Most of their ETGs have blue colors and show recent star formation. These observations reveal for the first time large fractions of spectroscopically confirmed star-forming blue ETGs in proto-clusters at z≈ 2. These star-forming ETGs are most likely among the progenitors of the quiescent population in clusters at more recent epochs. Their mass-size relation is consistent with that of passive ETGs in clusters at z̃ 0.7-1.5. If these galaxies are the progenitors of cluster ETGs at these lower redshifts, their size would evolve according to a similar mass-size relation. It is noteworthy that quiescent ETGs in clusters at z=1.8-2 also do not show any significant size evolution over this redshift range, contrary to field ETGs. The ETG fraction is ≲ 50%, compared to the typical quiescent ETG fraction of ≈ 80% in cluster cores at z< 1. The fraction, masses, and colors of the newly discovered ETGs imply that other cluster ETGs will be formed/accreted at a later time.
Volume
804
Issue
2
Start page
117
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...804..117M
Rights
open.access
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