Year: 2020
Type: article
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 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.
Source: The Astrophysical Journal
Authors: Behnam Darvish, Nick Z. Scoville, Christopher Martin, David Sobral, Bahram Mobasher, Alessandro Rettura, Jorryt Matthee, Peter Capak, Nima Chartab, Shoubaneh Hemmati, Daniel Masters, Hooshang Nayyeri, Donal O’Sullivan, Ana Paulino-Afonso, Zahra Sattari, Abtin Shahidi, Mara Salvato, Brian C. Lemaux, Olivier Le Fèvre, Olga Cucciati
Institutions: California Institute of Technology, Lancaster University, University of California, Riverside, W.M. Keck Observatory, ETH Zurich, Infrared Processing and Analysis Center, University of California, Irvine, Max Planck Institute for Extraterrestrial Physics, University of California, Davis, Centre National de la Recherche Scientifique, Aix-Marseille Université, Laboratoire d’Astrophysique de Marseille, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W3011783886