2018ApJ...855...48Q -
Astrophys. J., 855, 48-48 (2018/March-1)
Detection of dust condensations in the Orion Bar photon-dominated region.
QIU K., XIE Z. and ZHANG Q.
Abstract (from CDS):
We report Submillimeter Array dust continuum and molecular spectral line observations toward the Orion Bar photon-dominated region (PDR). The 1.2 mm continuum map reveals, for the first time, a total of nine compact (r < 0.01 pc) dust condensations located within a distance of ∼0.03 pc from the dissociation front of the PDR. Part of the dust condensations are also seen in spectral line emissions of CS (5-4) and H2CS (71,7-61,6), though the CS map also reveals dense gas further away from the dissociation front. We also detect compact emissions in H2CS (60,6-50,5), (62,4-52,3) and C34S, C33S (4-3) toward bright dust condensations. The line ratio of H2CS (60,6-50,5)/(62,4-52,3) suggests a temperature of 73 ± 58 K. A nonthermal velocity dispersion of ∼0.25-0.50 km s–1 is derived from the high spectral resolution C34S data and indicates a subsonic to transonic turbulence in the condensations. The masses of the condensations are estimated from the dust emission, and range from 0.03 to 0.3 M☉, all significantly lower than any critical mass that is required for self-gravity to play a crucial role. Thus the condensations are not gravitationally bound, and could not collapse to form stars. In cooperating with recent high-resolution observations of the compressed surface layers of the molecular cloud in the Bar, we speculate that the condensations are produced as a high-pressure wave induced by the expansion of the H II region compresses and enters the cloud. A velocity gradient along a direction perpendicular to the major axis of the Bar is seen in H2CS (71,7-61,6), and is consistent with the scenario that the molecular gas behind the dissociation front is being compressed.
Abstract Copyright:
© 2018. The American Astronomical Society. All rights reserved.
Journal keyword(s):
dust, extinction - ISM: individual objects: Orion Bar - ISM: molecules - ISM: structure - photon-dominated region PDR - stars: formation
Nomenclature:
Fig. 2, Table 1: [QXZ2018] SMAN (Nos SMA1-SMA9).
Simbad objects:
17
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