Oral Presentation

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

P. T. Anh (Vietnam National Satellite Center)

We report on high angular resolution observations of the CO(7–6) line and 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 simple lens models, we fit their parameters and the source morphology to the observed visibilities. We measure a molecular disk radius of 0.85 ± 0.12 kpc; the continuum (dust) is more compact and is only marginally resolved. Evidence for a significant ellipticity (3.3 standard deviations from circular) and for a velocity gradient (4.5 standard deviations from 0) has been obtained. The galaxy is found to have a very low dynamical mass, Mdyn = 4.7±1.4 × 10^9 Msun, together with low molecular gas mass and far-infrared (FIR) luminosity, Mgas = 2 to 4 10^9 MSun and LFIR = 13 × 10^11 Lsun respectively. Moreover, its large star formation efficiency places it on the high side of both low-z and high-z galaxies. Taken together, these results suggest that RXJ0911 is in a state where much of its gas has been exhausted after an intense star formation period, leaving it at the border between high-z and low-z quasar hosts. The way differential magnification affects these results is discussed.