The Warm Molecular Gas around the Cloverleaf Quasar
Abstract
We present the first broadband λ = 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 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, F ν = 14 mJy(ν/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 13CO upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2-50 × 109 M sun) of highly excited gas with thermal pressure nT > 106 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 20,2 → 11,1 transition at λrest = 303 μm.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2009
- DOI:
- 10.1088/0004-637X/705/1/112
- arXiv:
- arXiv:0908.1818
- Bibcode:
- 2009ApJ...705..112B
- Keywords:
-
- galaxies: ISM;
- instrumentation: spectrographs;
- ISM: clouds;
- stars: luminosity function;
- mass function;
- techniques: spectroscopic;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- ApJ in press, 12 pages in emulateApJ