Spectroscopic Confirmation of a Coma Cluster Progenitor at z ~ 2.2. (arXiv:2002.06207v1 [astro-ph.GA])

Spectroscopic Confirmation of a Coma Cluster Progenitor at z ~ 2.2. (arXiv:2002.06207v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Darvish_B/0/1/0/all/0/1">Behnam Darvish</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scoville_N/0/1/0/all/0/1">Nick Z. Scoville</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martin_C/0/1/0/all/0/1">Christopher Martin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sobral_D/0/1/0/all/0/1">David Sobral</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mobasher_B/0/1/0/all/0/1">Bahram Mobasher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rettura_A/0/1/0/all/0/1">Alessandro Rettura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matthee_J/0/1/0/all/0/1">Jorryt Matthee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Capak_P/0/1/0/all/0/1">Peter Capak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chartab_N/0/1/0/all/0/1">Nima Chartab</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hemmati_S/0/1/0/all/0/1">Shoubaneh Hemmati</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Masters_D/0/1/0/all/0/1">Daniel Masters</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nayyeri_H/0/1/0/all/0/1">Hooshang Nayyeri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+OSullivan_D/0/1/0/all/0/1">Donal O'Sullivan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Paulino_Afonso_A/0/1/0/all/0/1">Ana Paulino-Afonso</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sattari_Z/0/1/0/all/0/1">Zahra Sattari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shahidi_A/0/1/0/all/0/1">Abtin Shahidi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Salvato_M/0/1/0/all/0/1">Mara Salvato</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lemaux_B/0/1/0/all/0/1">Brian C. Lemaux</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fevre_O/0/1/0/all/0/1">Olivier Le Fevre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cucciati_O/0/1/0/all/0/1">Olga Cucciati</a>

We report the spectroscopic confirmation of a new protocluster in the COSMOS
field at $z$ $sim$ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as
an overdensity of narrow-band selected H$alpha$ emitting candidates. With only
two masks of Keck/MOSFIRE near-IR spectroscopy in both $H$ ($sim$ 1.47-1.81
$mu$m) and $K$ ($sim$ 1.92-2.40 $mu$m) bands ($sim$ 1.5 hour 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 $pm$ 0.00101 and
$sigma_{los}$=645 $pm$ 69 km s$^{-1}$ for this protocluster, respectively.
Assuming virialization and spherical symmetry for the system, we estimate a
total mass of $M_{vir}$ $sim$ $(1-2) times$10$^{14}$ $M_{odot}$ for the
structure. We evaluate a number density enhancement of $delta_{g}$ $sim$ 7
for this system and we argue that the structure is likely not fully virialized
at $z$ $sim$ 2.2. However, in a spherical collapse model, $delta_{g}$ is
expected to grow to a linear matter enhancement of $sim$ 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) $sim$
9.2$times$10$^{14}$ $M_{odot}$ by now. This observationally efficient
confirmation suggests that large narrow-band 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.

http://arxiv.org/icons/sfx.gif