The Warm Molecular Gas around the Cloverleaf Quasar

We present the first broadband λ = 1mm spectrum toward the z = 2.56 Cloverleaf Quasar, obtained with Z-Spec, a 1-mm grating spectrograph on the 10.4-meter Caltech Submillimeter Observatory. The 190–305 GHz observation band corresponds to rest-frame 272 to 444 μm, and we measure the dust continuum as well as all four transitions of carbon monoxide (CO) lying in this range. The power-law dust emission, Fν = 14mJy (ν/240GHz) 3.9 is consistent with the published continuum measurements. The CO J=6→5, J=8→7, and J=9→8 measurements are the first, and now provide the highest-J CO information in this source. Our measured CO intensities are very close to the previously-published interferometric measurements of J =7→ 6, and we use all available transitions and our CO upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2–50×10M⊙) of highly-excited gas with thermal pressure nT > 10Kcm. The ratio of the total CO cooling to the far-IR dust emission exceeds that in the local dusty galaxies, and we investigate the potential heating sources for this bulk of warm molecular gas. We conclude that both UV photons and X-rays likely contribute, and discuss implications for a top-heavy stellar initial mass function arising in the X-ray-irradiated starburst. Finally we present tentative identifications of other species in the spectrum, including a possible detection of the H2O 20,2→11,1 transition at λrest = 303 μm. Subject headings: ISM: clouds, galaxies: ISM, stars: luminosity function, mass function, instrumentation: spectrographs, techniques: spectroscopic