The molecular gas associated with the Orion bright bar

Abstract

view Abstract Citations (10) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Molecular Gas Associated with the Orion Bright Bar Omodaka, Toshihiro ; Hayashi, Masahiko ; Hasegawa, Telsuo ; Hayashi, Saeko S. Abstract Detailed studies of the shocked region associated with the Orion bright bar are presented. The millimeter wave spectral lines of (12)CO (J = 1-0), (13)CO (J = 1-0), CS (J = 2-1), HCO(+) (J = 1-0), and H51 alpha have been observed across the bright bar. The intensity of all the molecular species shows a rapid increase close to the ionization front and a significant falloff at a distance of approximately 50 sec farther out from it. This suggests the existence of a layer of dense molecular gas just outside the ionization front. This layer has a velocity redshifted by 1-2 km s-1 relative to the ambient molecular cloud, which can be due to acceleration by thermal and kinetic pressure from the H II region or due to a passage of a shock. The high-density molecular layer associated with the bar is probably a shock-compressed layer driven by the ionization front of M42. A multitransitional anaylsis of the CS emission shows that the H2 volume density of the molecular gas is larger than that of the ambient gas by a factor of 3. The apparent density enhancement of a factor of 3 in the shocked gas is too small for a radiative shock in a homogeneous medium; density inhomgeneities or clumpiness in the pre- and postshocked layer may account for this apparently small compression ratio. This layer is exposed to intense UV radiation from the Trapezium stars and a photodissocited region is formed between neutral layer and the ionization front. The similarity in distribution of the thermally excited H2 emissions arising from shock fronts and or dense phtotodissociation regions and the millimeter-wave molecular line emissions originating from cooled shock-compressed regions also supports the idea of homogeneity or clumpiness is the shocked cloud. The gas temperature of this shocked layer is about 100 K and is very high compared with other molecular clouds without an embedded heat source. Both shock heating and radiative heating may contribute to maintain this high temperature. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174400 Bibcode: 1994ApJ...430..256O Keywords: Interstellar Gas; Line Spectra; Molecular Clouds; Molecular Gases; Orion Nebula; Radio Spectra; Shock Fronts; Carbon Monoxide; Gas Temperature; H Ii Regions; Hydrogen; Shock Waves; Astrophysics; ISM: INDIVIDUAL NAME: ORION NEBULA; ISM: MOLECULES; RADIO LINES: ISM; SHOCK WAVES full text sources ADS | data products SIMBAD (4)