Volume 609, January 2018
|Number of page(s)||14|
|Section||Interstellar and circumstellar matter|
|Published online||22 December 2017|
Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde
III. The Orion molecular cloud 1⋆
1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
3 Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 830011 Urumqi, PR China
4 Astronomy Department, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
5 Department of Astronomy, Nanjing University, 210093 Nanjing, PR China
6 Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 210008 Nanjing, PR China
Received: 28 August 2017
Accepted: 22 September 2017
We mapped the kinetic temperature structure of the Orion molecular cloud 1 (OMC-1) with para-H2CO (JKaKc = 303–202, 322–221, and 321–220) using the APEX 12 m 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 ± 2 K at a spatial density of 105 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 (n(H2) ≳ 104 cm-3) 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.
Key words: stars: formation / stars: massive / ISM: clouds / ISM: molecules / radio lines: ISM
The reduced datacubes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A16
© ESO, 2017
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