Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe

Abstract

We present high-spatial-resolution (∼ 0.12 or ≈ 800 pc at z = 4.5) ALMA 870 µm dust continuum observations of a sample of 44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and HerMES far-infrared surveys because of their red colors from 250 to 500 µm: S 500 /S 250 > 1.5 and S 500 /S 350 > 1.0. With photometric redshifts in the range z ∼ 4-6, our sample includes the most luminous starbursting systems in the early Universe known so far, with total obscured starformation rates (SFRs) of up to ∼ 4, 500 M yr −1 , as well as a population of lensed, less intrinsically luminous sources. The lower limit on the number of ultrared DSFGs at 870 µm (with flux densities measured from the ALMA maps and thus not affected by source confusion) derived in this work is in reasonable agreement with models of galaxy evolution, whereas there have been reports of conflicts at 500 µm (where flux densities are derived from SPIRE). Ultrared DSFGs have a variety of morphologies (from relatively extended disks with smooth radial profiles, to compact sources, both isolated and interacting) and an average size, θ FWHM , of 1.46 ± 0.41 kpc, considerably smaller than the values reported in previous work for less-luminous DSFGs at lower redshifts. The size and the estimated gas-depletion times of our sources are compatible with their being the progenitors of the most massive, compact, red-and-dead galaxies at z ∼ 2-3, and ultimately of local ultra-massive elliptical galaxies or massive galaxy clusters. We are witnessing the birth of the high-mass tail of the red sequence of galaxies.

The Complete Redshift Distribution of Dusty Star-forming Galaxies from the SPT-SZ Survey

“…While the SPT sample includes some sources equivalent to those selected in the blank-field surveys, it also includes the previously undiscovered high redshift and extreme tail of DSFGs. In addition to discovering the highest-redshift DSFG to date (SPT0311-58 at z=6.9; Marrone et al 2018;Strandet et al 2017), and with 12 sources at z > 5, the SPT-DSFG catalog contains roughly half of the DSFGs discovered at z > 5 (Walter et al 2012;Riechers et al 2013Riechers et al , 2014Riechers et al , 2017Riechers et al , 2020Dowell et al 2014;Rawle et al 2014;Asboth et al 2016;Fudamoto et al 2017;Oteo et al 2017;Strandet et al 2017;Pavesi et al 2018;Zavala et al 2018;Jin et al 2019).…”

On the dust temperatures of high-redshift galaxies

“…Finally, we note that our sample does not include the most luminous submm galaxies that can have S 870µm fluxes of much higher than a few mJy (e.g. Oteo et al 2017;Oteo et al 2018) and, hence, we cannot rule out that T mw significantly exceeds 20-30 K in such objects. While submm-luminous galaxies are typically interpreted as having high SFRs, Eq.…”

The Complete Redshift Distribution of Dusty Star-forming Galaxies from the SPT-SZ Survey

“…While the SPT sample includes some sources equivalent to those selected in the blank-field surveys, it also includes the previously undiscovered high redshift and extreme tail of DSFGs. In addition to discovering the highest redshift DSFG to-date (SPT0311-58; Strandet et al 2017;Marrone et al 2017), the SPT DSFG catalog also contains roughly half of the z>5 DSFGs discovered (Oteo et al 2017;Asboth et al 2016;Walter et al 2012;Rawle et al 2014;Riechers et al 2013;Dowell et al 2014;Strandet et al 2017;Riechers et al 2014;Riechers et al 2017;Pavesi et al 2018;Jin et al 2019;Fudamoto et al 2017;Zavala et al 2018;Riechers et al 2020) A way to assess the relative rarity of SPTselected sources is to consider the space density. However, because the majority SPT-selected sources are lensed, the volume probed changes as a function of lensing and the effective volume is difficult to calculate.…”