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arXiv · 1709.07694

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1

X. D. Tang·C. Henkel·K. M. Menten·F. Wyrowski·N. Brinkmann·X. W. Zheng·Y. Gong·Y. X. Lin·J. Esimbek·J. J. Zhou·Y. Yuan·D. L. Li·Y. X. He
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Abstract

We mapped the kinetic temperature structure of the Orion molecular cloud 1 with para-H2CO(303-202, 322-221, and 321-220) using the APEX 12m telescope. This is compared with the temperatures derived from the ratio of the NH3(2,2)/(1,1) inversion lines and the dust emission. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured averaged line ratios of para-H2CO 322-221/303-202 and 321-220/303-202. The gas kinetic temperatures derived from the para-H2CO line ratios are warm, ranging from 30 to >200 K with an average of 62 K at a spatial density of 10$^5$ cm$^{-3}$. These temperatures are higher than those obtained from NH3(2,2)/(1,1) and CH3CCH(6-5) in the OMC-1 region. The gas kinetic temperatures derived from para-H2CO agree with those obtained from warm dust components measured in the mid infrared (MIR), which indicates that the para-H2CO(3-2) ratios trace dense and warm gas. The cold dust components measured in the far infrared (FIR) are consistent with those measured with NH3(2,2)/(1,1) and the CH3CCH(6-5) line series. With dust at MIR wavelengths and para-H2CO(3-2) on one side and dust at FIR wavelengths, NH3(2,2)/(1,1), and CH3CCH(6-5) on the other, dust and gas temperatures appear to be equivalent in the dense gas of the OMC-1 region, but provide a bimodal distribution, one more directly related to star formation than the other. The non-thermal velocity dispersions of para-H2CO are positively correlated with the gas kinetic temperatures in regions of strong non-thermal motion (Mach number >2.5) of the OMC-1, implying that the higher temperature traced by para-H2CO is related to turbulence on a 0.06 pc scale. Combining the temperature measurements with para-H2CO and NH3(2,2)/(1,1) line ratios, we find direct evidence for the dense gas along the northern part of the OMC-1 10 km s$^{-1}$ filament heated by radiation from the central Orion nebula.

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X. D. Tang, C. Henkel, K. M. Menten, F. Wyrowski, N. Brinkmann, X. W. Zheng, Y. Gong, Y. X. Lin, J. Esimbek, J. J. Zhou, Y. Yuan, D. L. Li, Y. X. He. 2017-09-22. Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1. https://doi.org/10.1051/0004-6361%2F201731849

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