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Title: Weak maser emission of methyl formate toward Sagittarius B2(N) in the green bank telescope PRIMOS survey

A non-LTE radiative transfer treatment of cis-methyl formate (HCOOCH{sub 3}) rotational lines is presented for the first time using a set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5-30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH{sub 3}-He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. A total of 49 low-lying transitions of methyl formate, with upper levels below 25 K, are identified. These lines are found to probe a presumably cold (∼30 K), moderately dense (∼10{sup 4} cm{sup –3}), and extended region surrounding Sgr B2(N). The derived column density of ∼4 × 10{sup 14} cm{sup –2} is only a factor of ∼10 larger than the column density of the trans conformer in the same source. Provided that the two conformers have the same spatial distribution, this result suggests that strongly non-equilibrium processes must be involved in their synthesis. Finally, our calculations show that all detected emission lines with a frequency below 30 GHz are (collisionally pumped) weak masers amplifying the continuum of Sgr B2(N). This result demonstrates the importance andmore » generality of non-LTE effects in the rotational spectra of complex organic molecules at centimeter wavelengths.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble F-38041 (France)
  2. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
  3. Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)
Publication Date:
OSTI Identifier:
22351327
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; COUPLED CHANNEL THEORY; DENSITY; EMISSION; FORMATES; GHZ RANGE; LTE; MASERS; MOLECULES; PROBES; RADIANT HEAT TRANSFER; SCATTERING; SPATIAL DISTRIBUTION; SPECTRA; SURFACES; SYNTHESIS; TELESCOPES; WAVELENGTHS