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Detection of HF emission from the Orion Bar
- Source :
- Astronomy & astrophysics, 537:L10. EDP Sciences
- Publication Year :
- 2012
- Publisher :
- EDP Sciences, 2012.
-
Abstract
- The clumpy density structure of photon-dominated regions is well established, but the physical properties of the clumps and of the surrounding interclump medium are only approximately known. The aim of this paper is to constrain the physical and chemical conditions in the Orion Bar, a prototypical nearby photon-dominated region. We present observations of the HF J=1-0 line, which appears in emission toward the Orion Bar, and compare the brightness of the line to non-LTE radiative transfer calculations. The large width of the HF line suggests an origin of the emission in the interclump gas, but collisional excitation by H2 in the interclump gas underpredicts the observed line intensity by factors of 3-5. In contrast, an origin of the line in the dense clumps requires a density of ~10^9 cm^-3, 10-100 times higher than previous estimates, which is unlikely. However, electron impact excitation reproduces our observations for T = 100 K and n(e) = 10 cm^-3, as expected for the interclump gas. We conclude that HF emission is a signpost of molecular gas with a high electron density. Similar conditions may apply to active galactic nuclei where HF also appears in emission.<br />Comment: Accepted for publication in A&A; 4 pages, 1 figure
- Subjects :
- ROTATIONAL-EXCITATION
Brightness
Electron density
Active galactic nucleus
FOS: Physical sciences
HYDROGEN-FLUORIDE
Astrophysics::Cosmology and Extragalactic Astrophysics
Astrophysics
PHOTODISSOCIATION REGIONS
HERSCHEL/HIFI OBSERVATIONS
STAR-FORMATION
CHEMICAL STRATIFICATION
Radiative transfer
EXTRAORDINARY SOURCES HEXOS
Collisional excitation
Astrophysics::Galaxy Astrophysics
Electron ionization
Line (formation)
Physics
astrochemistry
Astronomy and Astrophysics
Astrophysics - Astrophysics of Galaxies
LINE OBSERVATIONS
ISM: molecules
SUBMILLIMETER OBSERVATIONS
Space and Planetary Science
Astrophysics of Galaxies (astro-ph.GA)
MOLECULAR CLOUDS
Bar (unit)
Subjects
Details
- ISSN :
- 14320746 and 00046361
- Volume :
- 537
- Database :
- OpenAIRE
- Journal :
- Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....56d4e4302426e2f87e5751d1e154ce6a