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

Journal Article · Mon Mar 10 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/783/2/72· OSTI ID:22351327

Faure, A.; Wiesenfeld, L. ^[1]; Remijan, A. J. ^[2]; Szalewicz, K. ^[3]

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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)

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 and generality of non-LTE effects in the rotational spectra of complex organic molecules at centimeter wavelengths.

• OSTI ID: 22351327
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 783; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCURACY
COUPLED CHANNEL THEORY
DENSITY
EMISSION
FORMATES
GHZ RANGE
LTE
MASERS
MOLECULES
PROBES
RADIANT HEAT TRANSFER
SCATTERING
SPATIAL DISTRIBUTION
SPECTRA
SURFACES
SYNTHESIS
TELESCOPES
WAVELENGTHS