Observations of the formaldehyde emission in Orion-KL - Abundances, distribution, and kinematics of the dense gas in the Orion molecular ridge

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view Abstract Citations (49) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the Formaldehyde Emission in Orion-KL: Abundances, Distribution, and Kinematics of the Dense Gas in the Orion Molecular Ridge Mangum, Jeffrey G. ; Wootten, Alwyn ; Loren, Robert B. ; Wadiak, E. James Abstract The "hot core," "plateau," and "ridge" features in the Orion-KL molecular cloud have been mapped in 2 cm H2CO emission with a 6" synthesized beam. We have also observed all ΔJ = 1 millimeter wave transitions of H2CO and several of the H213CO and H2C18O transitions in the 211 to 363 GHz window toward Orion-KL with a single antenna. The H2CO hot core emission has been identified for the first time both in high- excitation line profiles and in the 2 cm maps. We identify a velocity shift in the 2 cm H2CO emission which we attribute to the plateau or bipolar flow. This velocity shift lies at a position angle of 120° ± 30°, which is parallel to the bipolar flows seen in SiO, HCO+, H2, SO2, CO, and SO emission. The large primary beam available for these observations has provided a particularly sensitive map of the rather extended "ridge" structure in Orion-KL. The "ridge" component in our 2 cm H2CO emission maps can be decomposed into two clumps, called the "compact ridge" and "10 km s-1 feature." The compact ridge dominates the observed emission. Comparison with aperture synthesis maps in other molecules demonstrates that the 2 cm H2CO compact ridge defines an extensive high-density (≳106 cm-3) region at the southern edge of the bipolar flow near IRc2. With this multitransition, multi-isotopomer^{5 }data set, we have modeled the spatial density in the compact ridge component. We find that n(H2) = 5.0 × 106-1.0 × 107 cm-3 in the H2CO compact ridge. These models also reveal that there is no evidence for substantial variation in the H2CO abundances among the hot core, compact ridge, and 10 km s-1 feature. However, H2CO is 3-25 times more abundant in these Orion-KL components than it is in other molecular clouds (Mundy et al.; Wootten et al.). This abundance enhancement may be due to the epidemic of massive star formation in the region. Observers have noted in the past that 2 cm H2CO emission occurs only rarely in interstellar clouds, though density sufficient to cause the emission is found in many cloud cores. We suggest that the reason the emission is notably intense in Orion-KL lies in the enhancement of the H2CO abundance, as well as in the high density. Publication: The Astrophysical Journal Pub Date: January 1990 DOI: 10.1086/168262 Bibcode: 1990ApJ...348..542M Keywords: Abundance; Formaldehyde; Kinematics; Molecular Clouds; Orion Nebula; Antennas; Astronomical Models; Emission Spectra; Gas Density; Interstellar Matter; Star Formation; interstellar: molecules; nebulae: abundances; nebulae: individual (Orion Nebula); Astrophysics; INTERSTELLAR: MOLECULES; NEBULAE: ABUNDANCES; NEBULAE: ORION NEBULA full text sources ADS | data products SIMBAD (2)