Resolving the molecular gas around the lensed quasar RXJ0911.4+0551

Abstract

We report on high angular resolution observations of the CO(7-6) line and millimeter continuum in the host galaxy of the gravitationally lensed (z ∼ 2.8) quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO observations resolve the molecular disk of the source. Using a lens model based on HST observations, we fit source models to the observed visibilities. We estimate a molecular disk radius of 1 ± 0.2 kpc and an inclination of 69 ± 6 deg, the continuum is more compact and is only marginally resolved by our observations. The relatively low molecular gas mass, Mgas = (2.3 ± 0.5) × 109 M·, and far-infrared (FIR) luminosity, LFIR = (7.2 ± 1.5) × 1011 L·, of this quasar could be explained by its relatively low dynamical mass, Mdyn = (3.9 ± 0.9) × 109 M·. It would be a scaled-down version the quasi-stellar objects (QSOs) usually found at high-z. The FIR and CO luminosities lie on the correlation found for QSOs from low to high redshifts and the gas-to-dust ratio (45 ± 17) is similar to the one measured in the z = 6.4 QSO, SDSS J1148+5251. Differential magnification affects the continuum-to-line luminosity ratio, the line profile, and possibly the spectral energy distribution. © 2013 ESO.