Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4

TL;DR

This study detects bright CO(4-3) emission in two high-redshift obscured quasars, revealing potential AGN-driven molecular winds and complex gas dynamics, contributing to understanding galaxy evolution in the early universe.

Contribution

First evidence of an AGN-driven molecular wind in a high-redshift quasar, with detailed analysis of gas kinematics and dynamics in two obscured QSOs at z>3.4.

Findings

SW022513 shows broad, blueshifted CO line indicating a possible AGN-driven wind.

SW022550 exhibits a double-peaked CO profile, suggestive of a merger or extended disk.

Both galaxies are gas-rich with large molecular gas masses, but have lower star-formation efficiencies.

Abstract

We report on the detection of bright CO(4-3) line emission in two powerful, obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at z>3.4. We analyze the line strength and profile to determine the gas mass, dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have found the first evidence for a molecular, AGN-driven wind in the early Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and blueshifted by -200 km/s relative to systemic (where the systemic velocity is estimated from the narrow components of ionized gas lines, as is commonly done for AGN at low and high redshifts). SW022550 has a more regular, double-peaked profile, which is marginally spatially resolved in our data, consistent with either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun, are large and account for <30% of the stellar mass, making these obscured QSOs as gas rich as other powerful CO emitting galaxies at high redshift, i.e., submillimeter galaxies. Our sources exhibit relatively lower star-formation efficiencies compared to other dusty, powerful starburst galaxies at high redshift. We speculate that this could be a consequence of the AGN perturbing the molecular gas.