THE WARM MOLECULAR GAS AROUND THE CLOVERLEAF QUASAR

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Abstract
We present the first broadband lambda = 1 mm spectrum toward the z = 2.56 Cloverleaf quasar, obtained with Z-Spec, a grating spectrograph on the 10.4 m Caltech Submillimeter Observatory. The 190-305 GHz observation band corresponds to the rest frame 272-444 mu m, 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, F-nu = 14 mJy (nu/240 GHz)(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)-C-13 upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2-50 x 10(9)M(circle dot)) of highly excited gas with thermal pressure nT > 10(6) K cm(-3). 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 2(0,2) -> 1(1,1) transition at lambda(rest) = 303 mu m.