2007/05/23 by Dominik A. Riechers, Fabian Walter, P. Cox +7 · 3 citations
Chemistry · Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Emission spectrum #Excited state #Galaxies: Formation, Evolution, Phenomena #Galaxy #Infrared #Line (geometry) #Luminosity #Optics #Photochemistry #Photodissociation #Physics #Plateau de Bure Interferometer #Quasar #Redshift #Spectral line #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/520335
published as Astrophys.J.666:778-783,2007 · 6 pages, 5 figures, 1 table, to appear in ApJ (accepted May 23, 2007)
arxiv created 2007/05/23 · openalex publication_date 2007/08/31 · arxiv updated 2009/12/01 · openalex created_date 2022/10/03 · openalex updated_date 2026/07/31
We report the detection of CN( N = 3 → 2) emission toward the Cloverleaf quasar ( z = 2.56) based on observations with the IRAM Plateau de Bure Interferometer. This is the first clear detection of emission from this radical at high redshift. CN emission is a tracer of dense molecular hydrogen gas [ n (H 2 ) > 10 4 cm -3 ] within star-forming molecular clouds, in particular, in regions where the clouds are affected by UV radiation. The HCN/CN intensity ratio can be used as a diagnostic for the relative importance of photodissociation regions (PDRs) in a source and as a sensitive probe of optical depth, the radiation field, and photochemical processes. We derive a lensing-corrected CN( N = 3 → 2) line luminosity of L = (4.5 ± 0.5) × 10 9 K km s -1 pc 2 . The ratio between CN luminosity and far-infrared luminosity falls within the scatter of the same relationship found for low- z (ultra-) luminous infrared galaxies. Combining our new results with CO( J = 3 → 2) and HCN( J = 1 → 0) measurements from the literature and assuming thermal excitation for all transitions, we find a CO/CN luminosity ratio of 9.3 ± 1.9 and a HCN/CN luminosity ratio of 0.95 ± 0.15. However, we find that the CN( N = 3 → 2) line is likely only subthermally excited, implying that those ratios may only provide upper limits for the intrinsic 1 → 0 line luminosity ratios. We conclude that, in combination with other molecular gas tracers like CO, HCN, and HCO + , CN is an important probe of the physical conditions and chemical composition of dense molecular environments at high redshift.