Molecular outflow in the reionization-epoch quasar J2054-0005 revealed by OH 119 $\mu$m observations

TL;DR

This study presents the first detection of a fast, spatially extended molecular outflow in a reionization-epoch quasar, revealing its potential to quench star formation and enrich the intergalactic medium.

Contribution

It provides the first spatially resolved observation of a molecular outflow in a $z>6$ quasar, demonstrating extremely high velocities and potential for galaxy evolution impact.

Findings

Detected a broad blue-shifted OH 119 μm absorption indicating an outflow.

Outflow velocities reach up to 1500 km/s, among the fastest at high redshift.

Outflow extends over 2 kpc and can escape into the intergalactic medium.

Abstract

Molecular outflows are expected to play a key role in galaxy evolution at high redshift. To study the impact of outflows on star formation at the epoch of reionization, we performed sensitive ALMA observations of OH 119 $\mu$m toward J2054-0005, a luminous quasar at $z=6.04$. The OH line is detected and exhibits a P-Cygni profile that can be fitted with a broad blue-shifted absorption component, providing unambiguous evidence of an outflow, and an emission component at near-systemic velocity. The mean and terminal outflow velocities are estimated to be $v_\mathrm{out}\approx670~\mathrm{km~s}^{-1}$ and $1500~\mathrm{km~s}^{-1}$, respectively, making the molecular outflow in this quasar one of the fastest at the epoch of reionization. The OH line is marginally spatially resolved for the first time in a quasar at $z>6$, revealing that the outflow extends over the central 2 kpc region. The mass outflow rate is comparable to the star formation rate ($\dot{M}_\mathrm{out}/\mathrm{SFR}\sim2$), indicating rapid ($\sim10^7~\mathrm{yr}$) quenching of star formation. The mass outflow rate in a sample star-forming galaxies and quasars at $4<z<6.4$ exhibits a positive correlation with the total infrared luminosity, although the scatter is large. Owing to the high outflow velocity, a large fraction (up to $\sim50\%$) of the outflowing molecular gas may be able to escape from the host galaxy into the intergalactic medium.