First detection of the [OI] 63-um emission from a redshift 6 dusty galaxy

TL;DR

This paper reports the first ground-based detection of the [OI] 63-um emission line from a galaxy at redshift 6, revealing its role as a major coolant and providing insights into early galaxy properties.

Contribution

It presents the first unambiguous ground-based detection of [OI] 63-um emission beyond redshift 3, demonstrating its potential for studying high-redshift dusty galaxies.

Findings

[OI] 63-um line detected at z=6.027 with luminosity (5.4±1.3)×10^9 L_sun

[OI] 63/[CII] ratio of 4 indicates dominant neutral gas cooling

High gas density and UV field strength comparable to lower redshift DSFGs

Abstract

We report a ground-based detection of the [OI] 63-um line in a z=6.027 gravitationally lensed dusty star-forming galaxy (DSFG) G09.83808 using the APEX SEPIA 660 receiver, the first unambiguous detection of the [OI]63 line beyond redshift 3, and the first obtained from the ground. The [OI]63 line is robustly detected at 22$\pm$5 Jy km s$^{-1}$, corresponding to an intrinsic (de-lensed) luminosity of $(5.4\pm1.3)\times10^{9}$ L$_\odot$. With the [OI]63/[CII] luminosity ratio of 4, the [OI]63 line is the main coolant of the neutral gas in this galaxy, in agreement with model predictions. The high [OI]63 luminosity compensates for the pronounced [CII] deficit ([CII]/FIR$\simeq4\times10^{-4}$). Using photon-dominated region models, we derive a source-averaged gas density $n=10^{4.0}$ cm$^{-3}$, and far-UV field strength $G=10^4 G_0$, comparable to the z=2-4 DSFG population. If G09.83808 represents a typical high-redshift DSFG, the [OI]63 line from z=6 non-lensed DSFGs should be routinely detectable in ALMA Band 9 observations with $\sim$15 min on-source, opening a new window to study the properties of the earliest DSFGs.