Detection of a high-redshift molecular outflow in a primeval hyperstarburst galaxy

TL;DR

This paper reports the discovery of a high-redshift molecular outflow in a hyperstarburst galaxy, revealing a transient, intense star formation phase with outflows unable to regulate star formation, suggesting rapid gas consumption.

Contribution

First detection of a high-redshift molecular outflow in a hyperstarburst galaxy using water absorption lines with ALMA, providing insights into extreme star formation and feedback processes.

Findings

Outflow rate of ~500 M_sun/year, lower than SFR, indicating saturated outflow capability.

Star formation rate surface density exceeds Eddington limit, implying a transient starburst phase.

Galaxy is a single starburst with a surrounding disc, not a merger.

Abstract

We report the discovery of a high-redshift, massive molecular outflow in the starburst galaxy SPT0346-52 ($z=5.656$) via the detected absorption of high-excitation water transitions (H$_2$O $4_{2,3}-4_{1,4}$ and H$_2$O $3_{3,0}-3_{2,1}$) with the Atacama Large Millimeter/submillimeter Array (ALMA). The host galaxy is one of the most powerful starburst galaxies at high redshift (star formation rate; SFR $\sim3,600$M$_\odot$year$^{-1}$), with an extremely compact ($\sim320$pc) star formation region and a star formation rate surface density ($\Sigma_{SFR}\sim5,500$M$_{\odot}~$year$^{-1}~$kpc$^{-2}$) five times higher than `maximum' (i.e. Eddington-limited) starbursts, implying a highly transient phase. The estimated outflow rate is $\sim500$M$_{\odot}$year$^{-1}$, which is much lower than the SFR, implying that in this extreme starburst the outflow capabilities saturate and the outflow is no longer capable of regulating star formation, resulting in a runaway process in which star formation will use up all available gas in less than 30Myr. Finally, while previous kinematic investigations of this source revealed possible evidence for an ongoing major merger, the coincidence of the hyper-compact starburst and high-excitation water absorption indicates that this is a single starburst galaxy surrounded by a disc.