A Caltech Library Service

Spectroscopic Confirmation of a Coma Cluster Progenitor at z ∼ 2.2

Darvish, Behnam and Scoville, Nick Z. and Martin, Christopher and Sobral, David and Mobasher, Bahram and Rettura, Alessandro and Matthee, Jorryt and Capak, Peter and Chartab, Nima and Hemmati, Shoubaneh and Masters, Daniel and Nayyeri, Hooshang and O’Sullivan, Donal and Paulino-Afonso, Ana and Sattari, Zahra and Shahidi, Abtin and Salvato, Mara and Lemaux, Brian C. and Le Fèvre, Olivier and Cucciati, Olga (2020) Spectroscopic Confirmation of a Coma Cluster Progenitor at z ∼ 2.2. Astrophysical Journal, 892 (1). Art. No. 8. ISSN 1538-4357. doi:10.3847/1538-4357/ab75c3.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We report the spectroscopic confirmation of a new protocluster in the COSMOS field at z ~ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as an overdensity of narrowband selected Hα emitting candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both H (~1.47–1.81 μm) and K (~1.92–2.40 μm) bands (~1.5 hr each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N > 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift and a line-of-sight velocity dispersion of z_(mean) = 2.23224 ± 0.00101 and σ_(los) = 645 ± 69 km s−1 for this protocluster, respectively. Assuming virialization and spherical symmetry for the system, we estimate a total mass of M_(vir) ~ (1–2) ×10¹⁴ M⊙ for the structure. We evaluate a number density enhancement of δ g ~ 7 for this system and we argue that the structure is likely not fully virialized at z ~ 2.2. However, in a spherical collapse model, δ g is expected to grow to a linear matter enhancement of ~1.9 by z = 0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of M_(dyn)(z = 0) ~ 9.2 × 10¹⁴ M⊙ by now. This observationally efficient confirmation suggests that large narrowband emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Darvish, Behnam0000-0003-4919-9017
Scoville, Nick Z.0000-0002-0438-3323
Martin, Christopher0000-0002-8650-1644
Sobral, David0000-0001-8823-4845
Rettura, Alessandro0000-0002-5615-256X
Matthee, Jorryt0000-0003-2871-127X
Capak, Peter0000-0003-3578-6843
Chartab, Nima0000-0003-3691-937X
Hemmati, Shoubaneh0000-0003-2226-5395
Masters, Daniel0000-0001-5382-6138
Nayyeri, Hooshang0000-0001-8242-9983
O’Sullivan, Donal0000-0002-4959-9179
Paulino-Afonso, Ana0000-0002-0943-0694
Sattari, Zahra0000-0002-0364-1159
Shahidi, Abtin0000-0001-6975-6293
Salvato, Mara0000-0001-7116-9303
Lemaux, Brian C.0000-0002-1428-7036
Le Fèvre, Olivier0000-0001-5891-2596
Cucciati, Olga0000-0002-9336-7551
Additional Information:© 2020 The American Astronomical Society. Received 2019 July 27; revised 2020 January 17; accepted 2020 February 10; published 2020 March 19. We are thankful to the anonymous referee for useful comments and suggestions that improved the quality of this paper. B.D. acknowledges financial support from NASA through the Astrophysics Data Analysis Program (ADAP), grant number NNX12AE20G, and the National Science Foundation, grant number 1716907. B.D. is thankful to Andreas Faisst, Laura Danly, and Matthew Burlando for their companionship during the observing run. B.D. is grateful to the COSMOS team for their useful comments during the team meeting in New York City 2019 May 14–17. A.R. research was made possible by Friends of W. M. Keck Observatory who philanthropically support the Keck Science Collaborative (KSC) fund. The observations presented herein were obtained at the W. M. Keck Observatory (program C236, PI Scoville), which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors would like to recognize and acknowledge the very prominent cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are fortunate to have the opportunity to perform observations from this mountain.
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Space Astrophysics Laboratory
Funding AgencyGrant Number
W. M. Keck ObservatoryUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Galaxy clusters ; High-redshift galaxy clusters ; High-redshift galaxies ; Large-scale structure of the universe ; Galaxy evolution ; Star formation ; Galaxy environments
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Galaxy clusters (584); High-redshift galaxy clusters (2007); High-redshift galaxies (734); Large-scale structure of the universe (902); Galaxy evolution (594); Star formation (1569); Galaxy environments (2029)
Record Number:CaltechAUTHORS:20200320-071214007
Persistent URL:
Official Citation:Behnam Darvish et al 2020 ApJ 892 8
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102008
Deposited By: Tony Diaz
Deposited On:20 Mar 2020 15:53
Last Modified:16 Nov 2021 18:07

Repository Staff Only: item control page