Witnessing the birth of the red sequence: ALMA high-resolution imaging of [CII] and dust in two interacting ultra-red starbursts at z = 4.425

TL;DR

This study uses ALMA's high-resolution imaging to analyze the morphology, dynamics, and physical properties of gas and dust in a distant, ultra-red starburst galaxy, shedding light on early galaxy formation and the birth of the red sequence.

Contribution

First high-resolution ALMA imaging of [CII] and dust in an ultra-red starburst at z=4.425, revealing detailed ISM morphology and dynamics in an early Universe galaxy.

Findings

Gas is more irregular and extended than dust.

ISM shows signs of ordered rotation and turbulence.

Supports merger-driven starburst scenario.

Abstract

Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array (ALMA), we have studied the morphology and the physical scale of the interstellar medium - both gas and dust - in SGP38326, an unlensed pair of interacting starbursts at $z= 4.425$. SGP38326 is the most luminous star bursting system known at $z > 4$ with an IR-derived ${\rm SFR \sim 4300 \,} M_\odot \, {\rm yr}^{-1}$. SGP38326 also contains a molecular gas reservoir among the most massive ever found in the early Universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at $z \sim 3$. Probing scales of $\sim 0.1"$ or $\sim 800 \, {\rm pc}$ we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [CII] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [CII] emission reveals that the dynamics of the two components of SGP38326 are compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.