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

¹ INAF – IASF Milano, via E. Bassini, 20133 Milan, Italy
e-mail: polletta@iasf-milano.inaf.it
² Institut d’Astrophysique Spatiale, Université de Paris XI, 91405 Orsay Cedex, France
³ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d’Hères, France
⁴ Institut d’Astrophysique de Paris, CNRS & Université Pierre et Marie Curie, 98bis, bd. Arago, 75014 Paris, France
⁵ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

Received: 5 January 2011
Accepted: 8 June 2011

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^-1) and blueshifted by −200 km s^-1 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, 4 × 10¹⁰ M_⊙, 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.