Kinetic temperature of massive star forming molecular clumps measured with formaldehyde

Wyrowski

et al. 2018

A&A

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Context. Formaldehyde (H 2 CO) is a reliable tracer to accurately measure the physical parameters of dense gas in star-forming regions. Aims. We aim to determine directly the kinetic temperature and spatial density with formaldehyde for the ∼100 brightest ATLASGALselected clumps (the TOP100 sample) at 870 µm representing various evolutionary stages of high-mass star formation. Methods. Ten transitions (J = 3-2 and 4-3) of ortho-and para-H 2 CO near 211, 218, 225, and 291 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope. Results. Using non-LTE models with RADEX, we derived the gas kinetic temperature and spatial density with the measured para-H 2 CO 3 21 -2 20 /3 03 -2 02 , 4 22 -3 21 /4 04 -3 03 , and 4 04 -3 03 /3 03 -2 02 ratios. The gas kinetic temperatures derived from the para-H 2 CO 3 21 -2 20 /3 03 -2 02 and 4 22 -3 21 /4 04 -3 03 line ratios are high, ranging from 43 to >300 K with an unweighted average of 91 ± 4 K. Deduced T kin values from the J = 3-2 and 4-3 transitions are similar. Spatial densities of the gas derived from the para-H 2 CO 4 04 -3 03 /3 03 -2 02 line ratios yield 0.6-8.3 × 10 6 cm −3 with an unweighted average of 1.5 (±0.1) × 10 6 cm −3 . A comparison of kinetic temperatures derived from para-H 2 CO, NH 3 , and dust emission indicates that para-H 2 CO traces a distinctly higher temperature than the NH 3 (2,2)/(1,1) transitions and the dust, tracing heated gas more directly associated with the star formation process. The H 2 CO line widths are found to be correlated with bolometric luminosity and increase with the evolutionary stage of the clumps, which suggests that higher luminosities tend to be associated with a more turbulent molecular medium. It seems that the spatial densities measured with H 2 CO do not vary significantly with the evolutionary stage of the clumps. However, averaged gas kinetic temperatures derived from H 2 CO increase with time through the evolution of the clumps. The high temperature of the gas traced by H 2 CO may be mainly caused by radiation from embedded young massive stars and the interaction of outflows with the ambient medium. For L bol /M clump 10 L ⊙ /M ⊙ , we find a rough correlation between gas kinetic temperature and this ratio, which is indicative of the evolutionary stage of the individual clumps. The strong relationship between H 2 CO line luminosities and clump masses is apparently linear during the late evolutionary stages of the clumps, indicating that L H 2 CO does reliably trace the mass of warm dense molecular gas. In our massive clumps H 2 CO line luminosities are approximately linearly correlated with bolometric luminosities over about four orders of magnitude in L bol , which suggests that the mass of dense molecular gas traced by the H 2 CO line luminosity is well correlated with star formation.

Section: Comparison Of Kinetic Temperatures Derived From Gas and Dustsupporting

confidence: 92%

Section: Variations Of Spatial Density and H 2 Co Abundancesupporting

confidence: 91%

Section: Variations Of Spatial Density and H 2 Co Abundancesupporting

confidence: 86%

Section: Opacities Of H 2 Comentioning

confidence: 99%

Section: Kinetic Temperaturementioning

confidence: 99%

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ATLASGAL-selected massive clumps in the inner Galaxy

Wyrowski

et al. 2018

A&A

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Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Chen

et al. 2017

A&A

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Context. The kinetic temperature of molecular clouds is a fundamental physical parameter affecting star formation and the initial mass function. The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. Aims. The classical dense molecular gas thermometer NH 3 is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Methods. Three rotational transitions (J K A K C = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 ) of para-H 2 CO near 218 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope toward six star forming regions in the LMC. Those data are complemented by C 18 O 2-1 spectra. Results. Using non-LTE modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H 2 CO 3 21 -2 20 /3 03 -2 02 and para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H 2 CO line could be detected, the gas kinetic temperatures derived from the preferred para-H 2 CO 3 21 -2 20 /3 03 -2 02 line ratios range from 35 to 63 K with an average of 47 ± 5 K (errors are unweighted standard deviations of the mean). Spatial densities of the gas derived from the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 line ratios yield 0.4 -2.9 × 10 5 cm −3 with an average of 1.5 ± 0.4 × 10 5 cm −3 . Temperatures derived from the para-H 2 CO line ratio are similar to those obtained with the same method from Galactic star forming regions and agree with results derived from CO in the dense regions (n(H 2 ) > 10 3 cm −3 ) of the LMC. A comparison of kinetic temperatures derived from para-H 2 CO with those from the dust also shows good agreement. This suggests that the dust and para-H 2 CO are well mixed in the studied star forming regions. A comparison of kinetic temperatures derived from para-H 2 CO 3 21 -2 20 /3 03 -2 02 and NH 3 (2,2)/(1,1) shows, however, a drastic difference. In the star forming region N159W, the gas temperature derived from the NH 3 (2,2)/(1,1) line ratio is ∼16 K (Ott et al. 2010), which is only half the temperature derived from para-H 2 CO and the dust. Furthermore, ammonia shows a very low abundance in a 30 ′′ beam. Apparently, ammonia only survives in the most shielded pockets of dense gas not yet irradiated by UV photons, while formaldehyde, less affected by photodissociation, is more widespread and is also sampling regions more exposed to the radiation of young massive stars. A correlation between the gas kinetic temperatures derived from para-H 2 CO and infrared luminosity, represented by the 250 µm flux, suggests that the kinetic temperatures traced by para-H 2 CO are correlated with the ongoing massive star formation in the LMC.

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Menten

et al. 2017

A&A

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We mapped the kinetic temperature structure of the Orion molecular cloud 1 (OMC-1) with para-H 2 CO (J KaKc = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 ) using the APEX 12 m telescope. This is compared with the temperatures derived from the ratio of the NH 3 (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-H 2 CO 3 22 -2 21 /3 03 -2 02 and 3 21 -2 20 /3 03 -2 02 . The gas kinetic temperatures derived from the para-H 2 CO line ratios are warm, ranging from 30 to >200 K with an average of 62 ± 2 K at a spatial density of 10 5 cm −3 . These temperatures are higher than those obtained from NH 3 (2,2)/(1,1) and CH 3 CCH (6-5) in the OMC-1 region. The gas kinetic temperatures derived from para-H 2 CO agree with those obtained from warm dust components measured in the mid infrared (MIR), which indicates that the para-H 2 CO (3-2) ratios trace dense and warm gas. The cold dust components measured in the far infrared (FIR) are consistent with those measured with NH 3 (2,2)/(1,1) and the CH 3 CCH (6-5) line series. With dust at MIR wavelengths and para-H 2 CO (3-2) on one side and dust at FIR wavelengths, NH 3 (2,2)/(1,1), and CH 3 CCH (6-5) on the other, dust and gas temperatures appear to be equivalent in the dense gas (n(H 2 ) 10 4 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-H 2 CO 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-H 2 CO is related to turbulence on a ∼0.06 pc scale. Combining the temperature measurements with para-H 2 CO and NH 3 (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.