A massive core for a cluster of galaxies at a redshift of 4.3

Abstract

Massive galaxy clusters have been found that date to times as early as three billion years after the Big Bang, containing stars that formed at even earlier epochs. The high-redshift progenitors of these galaxy clusters-termed 'protoclusters'-can be identified in cosmological simulations that have the highest overdensities (greater-than-average densities) of dark matter. Protoclusters are expected to contain extremely massive galaxies that can be observed as luminous starbursts . However, recent detections of possible protoclusters hosting such starbursts do not support the kind of rapid cluster-core formation expected from simulations : the structures observed contain only a handful of starbursting galaxies spread throughout a broad region, with poor evidence for eventual collapse into a protocluster. Here we report observations of carbon monoxide and ionized carbon emission from the source SPT2349-56. We find that this source consists of at least 14 gas-rich galaxies, all lying at redshifts of 4.31. We demonstrate that each of these galaxies is forming stars between 50 and 1,000 times more quickly than our own Milky Way, and that all are located within a projected region that is only around 130 kiloparsecs in diameter. This galaxy surface density is more than ten times the average blank-field value (integrated over all redshifts), and more than 1,000 times the average field volume density. The velocity dispersion (approximately 410 kilometres per second) of these galaxies and the enormous gas and star-formation densities suggest that this system represents the core of a cluster of galaxies that was already at an advanced stage of formation when the Universe was only 1.4 billion years old. A comparison with other known protoclusters at high redshifts shows that SPT2349-56 could be building one of the most massive structures in the Universe today.

A Noncorotating Gas Component in an Extreme Starburst at z = 4.3

“…On the other hand, our finding of a non-corotating gas component does not necessarily reject the possibility that COSMOS-AzTEC-1 experiences another major merger in the past, which is an important mechanism to explain extreme starbursts with SFR∼ 1000 M ⊙ yr −1 (e.g., Hayward et al 2013;Cibinel et al 2019) and/or clump formation at high-redshift (Calabrò et al 2019). Recent observations discover a group of ∼10 gasrich galaxies within 200-300 kpc around a bright SMG at z ∼ 4 (Oteo et al 2018, Miller et al 2018, see also Capak et al 2011, Hodge et al 2013, Brisbin et al 2017, Wardlow et al 2018, Casey et al 2019 for discoveries of gas-rich companions around dusty star-forming galaxies at high-redshift). In such high-density environments, gas-rich major mergers are naturally expected to occur and then trigger an extreme starburst in the central galaxy of protoclusters.…”

The East Asian Observatory SCUBA-2 Survey of the COSMOS Field: Unveiling 1147 Bright Sub-millimeter Sources across 2.6 Square Degrees

“…If such structures do exist within the S2COSMOS source catalogue then they remain interesting in the context of galaxy evolution (e.g. Smail et al 2014;Casey et al 2015;Ma et al 2015;Lewis et al 2018;Oteo et al 2018;Miller et al 2018) but their identification requires precise 3-D locations for each SMG, which lies beyond the scope of this paper. Pin-pointing the location of each galaxy that contributes to a source in S2COSMOS catalogue can be achieved with high-resolution interferometric imaging at sub-mm wavelengths (e.g.…”

SCUBA-2 Ultra Deep Imaging EAO Survey (Studies). III. Multiwavelength Properties, Luminosity Functions, and Preliminary Source Catalog of 450 μm Selected Galaxies

“…SMGs also dominate the massive-end of star formation main sequence (Swinbank et al 2004;Tacconi et al 2006Tacconi et al , 2008Hainline et al 2011;Micha lowski et al 2012aMicha lowski et al , 2017da Cunha et al 2015;Dunlop et al 2017) with SFRs ranging from 100 to > 1000 M yr −1 (Micha lowski et al 2010;Hainline et al 2011;Barger et al 2012;Simpson et al 2015). Furthermore, clustering analyzes have revealed that SMGs reside in high-mass (10 12 -10 13 h −1 M ) dark matter halos Farrah et al 2006;Magliocchetti et al 2007;Hickox et al 2012;Chen et al 2016a;Wilkinson et al 2017), suggesting that SMGs may be the progenitors of elliptical galaxies in the local Universe (Miller et al 2018). Despite these progresses, our understanding of this population is still incomplete in their number counts (Karim et al 2013), stellar masses (Micha lowski et al 2012a(Micha lowski et al , 2014Zhang et al 2018), and triggering mechanism of the star formation (Targett et al 2011(Targett et al , 2013Hodge et al 2016), especially at the faint and high-redshift ends.…”