Gas properties in the Early Universe deciphered from spectral line surveys of high-z objects: The Cloverleaf Quasar

Molecular lines observed in remote quasars arise from exceptionnally strong starburst regions in the vicinity of the QSO. Their study offers a unique opportunity to probe the gas physical and chemical properties at the epoch of peak star formation (z=2-3). We report the preliminary results of an on-going mm/sub-mm spectral line survey of the Cloverleaf Quasar (z=2.6), the archetype of gravitationally lensed quasars. We identify 14 molecular species, including rare isotopologues of CO and HCO+. The high gas density tracers HCO+, HCN, HNC and CN are detected through several rotational transitions, up to J=8-7 (Eup/k ≃ 155 K). Their emission appears to arise from dense (> 106 cm−3) gas clumps embedded in a circumnuclear disk with a flat rotation curve