Molecular Outflows in z > 6 QSO Hosts Driven by Star Formation

TL;DR

This study presents ALMA detections of molecular outflows in three z > 6 QSO hosts, revealing outflow properties comparable to those in dusty star-forming galaxies and exploring the potential influence of AGN activity.

Contribution

First detection of molecular outflows in z > 6 QSO hosts using OH 119 micron absorption, expanding understanding of feedback in early massive galaxies.

Findings

Molecular outflows have similar mass outflow rates to high-z dusty star-forming galaxies.

Outflows are driven primarily by star formation, with limited evidence for AGN influence.

Differences in spectral properties may be due to host dust continuum structure.

Abstract

Feedback and outflows in galaxies that are associated with a quasar phase are expected to be pivotal in quenching the most massive galaxies. However, observations targeting the molecular outflow phase, which dominates both the mass and momentum and removes the immediate fuel for star formation, are limited in high-z QSO hosts. Massive quiescent galaxies found at z ~ 4 are predicted to have already quenched star formation by z ~ 5 and undergone their most intense growth at z > 6. Here, we present two ALMA detections of molecular outflows, traced by blue-shifted absorption of the OH 119 micron doublet, from a sample of three z > 6 infrared luminous QSO hosts: J2310+1855 and P183+05. OH 119 micron is also detected in emission in P183+05, and tentatively in the third source: P036+03. Using similar assumptions as for high-z Dusty Star-Forming Galaxy outflows, we find that our QSOs drive molecular outflows with comparable mass outflow rates, and that are comparably energetic except for J2310+1855's significantly lower outflow energy flux. We do not find evidence, nor require additional input from the central AGN to drive the molecular outflow in J2310+1855 but can not rule out an AGN contribution in P183+05 if a significant AGN contribution to L_FIR is assumed and/or if the outflow covering fraction is high (> 53%), which evidence from the literature suggests is unlikely in these sources. Differences observed in the blue-shifted absorption spectral properties may instead be caused by the QSO hosts' more compact dust continuum, limiting observations to lower altitude and more central regions of the outflow.