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Spectroscopic Confirmation of a Coma Cluster Progenitor at z ~ 2.2

Journal
Date Issued
2020
Author(s)
Darvish, Behnam
•
Scoville, Nick Z.
•
Martin, Christopher
•
Sobral, David
•
Mobasher, Bahram
•
Rettura, Alessandro
•
Matthee, Jorryt
•
Capak, Peter
•
Chartab, Nima
•
Hemmati, Shoubaneh
•
Masters, Daniel
•
Nayyeri, Hooshang
•
O'Sullivan, Donal
•
Paulino-Afonso, Ana
•
Sattari, Zahra
•
Shahidi, Abtin
•
Salvato, Mara
•
Lemaux, Brian C.
•
Fèvre, Olivier Le
•
DOI
Abstract
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 sigma_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) x 10^14 M_sun 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 x 10^14 M_sun 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.
Volume
892
Issue
1
Start page
8
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2020ApJ...892....8D
Rights
open.access
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