2013A&A...552L..12A

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±0.2kpc and an inclination of 69±6°, the continuum is more compact and is only marginally resolved by our observations. The relatively low molecular gas mass, M_gas=(2.3 ±0.5)x10⁹M_☉, and far-infrared (FIR) luminosity, L_FIR=(7.2±1.5)x10¹¹L_☉, of this quasar could be explained by its relatively low dynamical mass, M_dyn=(3.9±0.9)x10⁹M_☉. 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, SDSSJ1148+5251. Differential magnification affects the continuum-to-line luminosity ratio, the line profile, and possibly the spectral energy distribution.