Galaxy growth in a massive halo in the first billion years of cosmic history

Abstract

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field 1-3 . Observing these structures during their period of active growth and assembly-the first few hundred million years of the Universe-is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far 4, 5 . Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 Myr after the Big Bang) that was discovered in a wide-field survey 6 . High-resolution imaging reveals this source to be a pair of extremely massive star-forming galaxies. The larger of these galaxies is forming stars at a rate of 2900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of just 8 kiloparsecs. This merging companion hosts 35

RELICS: Reionization Lensing Cluster Survey

“…While [C ii] is associated with neutral H i gas in photodissociation regions (PDRs), [O iii] is associated with ionized H ii gas, more prevalent in higher redshift, lower metallicity galaxies with higher ionization states (Harikane et al 2018). As predicted, ALMA's highest-redshift spectroscopic confirmations have come from [O iii], and the six z > 6 galaxies targeted to date have all yielded [O iii] detections at z = 6.900 (Marrone et al 2018); z = 7.107 (Carniani et al 2017); z = 7.212 (Inoue et al 2016); z = 8.312 (Tamura et al 2018); z = 8.382 (Laporte et al 2017a); and z = 9.11 (Hashimoto et al 2018b). The two highest redshift detections are lensed galaxies.…”

An Extremely Massive Quiescent Galaxy at z = 3.493: Evidence of Insufficiently Rapid Quenching Mechanisms in Theoretical Models*

“…In Figure 4, we explore this possibility for a sample of high-redshift DSFGs with published stellar masses, molecular gas masses, and star formation rates (Capak et al 2011;Riechers et al 2013;Cooray et al 2014;Ma et al 2015;Riechers et al 2017;Strandet et al 2017;Marrone et al 2018;Williams et al 2019;Jin et al 2019). These systems have masses consistent with the mass evolution of XMM-2599 derived from our best-fit SFH.…”

“…The leading candidates for progenitors of these galaxies, which clearly must form stellar mass at extreme rates at early times, are high-redshift dusty star-forming galaxies (DSFGs). Recent ALMA observations of small numbers of these DSFGs at 5 < z < 7 reveal large amounts of molecular gas and extreme star formation rates (e.g., Capak et al 2011;Riechers et al 2013Riechers et al , 2017Strandet et al 2017;Marrone et al 2018). The lack of deep stellar continuum spectra for these z > 3 UMGs however (3 UMGs with absorption features robustly detected; Glazebrook et al 2017, S18) has prevented establishment of a firm link between these objects and the DSFGs, as photometric studies cannot robustly infer the past star-formation history.…”

Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85

“…The halo masses are then extrapolated from the total baryonic masses using two methods, both rather conservative; these are the same assumptions as used to estimate the halo mass of SPT0311, the most distant DSFG (Marrone et al 2018). The first sets an absolute floor to the halo mass by assuming the cosmic baryon fraction f b = 0.19 (Planck Collaboration et al 2016) and converting from the median baryonic mass total calculated in all cases.…”

“…However, the identification of these Dusty Star-Forming Galaxies (DSFGs) out to higher redshifts (z > ∼ 4), in the first two Gyr after the Big Bang, has proven exceedingly difficult. While extraordinary discoveries of DSFGs exist out to z ∼ 7 (SPT0311 being the highest-z DSFG found to-date, Strandet et al 2017;Marrone et al 2018), their total contribution to the cosmic star-formation budget is unconstrained during this early epoch (Casey et al 2018b). Contradictory results have been presented in the literature, with some claiming that DSFGs play an insignificant role in z > 4 star-formation with less than 10% of the total (e.g.…”