2009/08/31 by C. M. Bradford, James Aguirre, J. E. Aguirre +14 · 6 citations
Physics and Astronomy · #Astrobiology #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Physics #Quasar #astro-ph.CO #astro-ph.IM
paper · pdf · doi:10.1088/0004-637x/705/1/112
ApJ in press, 12 pages in emulateApJ
arxiv created 2009/09/08 · openalex publication_date 2009/10/08 · arxiv updated 2015/05/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 13 CO upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2–50 × 10 9 M ☉ ) 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 H 2 O \2 0,2 → 1 1,1 transition at λ rest = 303 μm.