Megaparsec-scale structure around the protocluster core SPT2349–56 at z = 4.3

Abstract

We present an extensive ALMA spectroscopic follow-up programme of the $z\, {=}\, 4.3$ structure SPT2349–56, one of the most actively star-forming protocluster cores known, to identify additional members using their [C ii] 158 μm and CO(4–3) lines. In addition to robustly detecting the 14 previously published galaxies in this structure, we identify a further 15 associated galaxies at $z\, {=}\, 4.3$, resolving 55$\, {\pm }\,$5 per cent of the 870 μm flux density at 0.5 arcsec resolution compared to 21 arcsec single-dish data. These galaxies are distributed into a central core containing 23 galaxies extending out to 300 kpc in diameter, and a northern extension, offset from the core by 400 kpc, containing three galaxies. We discovered three additional galaxies in a red Herschel-SPIRE source 1.5 Mpc from the main structure, suggesting the existence of many other sources at the same redshift as SPT2349–56 that are not yet detected in the limited coverage of our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9$\pm 5)\, {\times }\, 10^{12}$ M⊙, while the two offset galaxy groups are about 30 and 60 per cent less massive and show significant velocity offsets from the central group. We calculate the [C ii] and far-infrared number counts, and find evidence for a break in the [C ii] luminosity function. We estimate the average SFR density within the region of SPT2349–56 containing single-dish emission (a proper diameter of 720 kpc), assuming spherical symmetry, to be roughly 4$\, {\times }\, 10^4$ M⊙ yr−1 Mpc−3; this may be an order of magnitude greater than the most extreme examples seen in simulations.

ALMA Observations of Lyα Blob 1: Multiple Major Mergers and Widely Distributed Interstellar Media

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A Massive Quiescent Galaxy Confirmed in a Protocluster at z = 3.09

“…The velocity distribution and halo mass of the AzTEC14 group are similar to those of SPT234956, which is known as an extreme overdensity of SMGs at z = 4.3 (Miller et al 2018;Hill et al 2020). Rotermund et al (2021) shows that the stellar mass of the most massive member and total stellar mass of SPT234956 are at least -…”

FIR-luminous [C ii] Emitters in the ALMA-SCUBA-2 COSMOS Survey (AS2COSMOS): The Nature of Submillimeter Galaxies in a 10 Comoving Megaparsec-scale Structure at z ∼ 4.6

“…Submillimeter galaxies (SMGs) are dusty strongly starforming galaxies at high redshift (e.g., Smail et al 1997;Barger et al 1998;Hughes et al 1998;Scott et al 2010;Yun et al 2012), which are believed to be tracers of massive dark-matter halos in the early universe (Blain et al 1999;Hickox et al 2012;Chen et al 2016;Wilkinson et al 2017;An et al 2019;Dudzevičiūtė et al 2020). As such, SMGs are potential signposts to identify large-scale structures (Tamura et al 2009;Umehata et al 2014Umehata et al , 2015Umehata et al , 2019Casey et al 2014;Casey 2016;Miller et al 2018;Oteo et al 2018;Cooke et al 2019;Hill et al 2020;Miller et al 2020) and also provide insights into the formation processes of massive galaxies. The majority of SMGs are found at z=1-4 and they are thought to be powered by gas-rich mergers or rapid gas accretion from the cosmic web (e.g., Tacconi et al 2008;Umehata et al 2019;McAlpine et al 2019).…”