Kinetic temperature of massive star forming molecular clumps measured with formaldehyde

Abstract

For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature.We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps.Three 218 GHz transitions (JKAKC=303-202, 322-221, and 321-220) of para-H2CO were observed with the 15m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H2CO 322-221/303-202and 321-220/303-202 ratios. The gas kinetic temperatures derived from the para-H2CO (321-220/303-202) line ratios range from 30 to 61 K with an average of 46 K. A comparison of kinetic temperature derived from para-H2CO, NH3, and the dust emission indicates that in many cases para-H2CO traces a similar kinetic temperature to the NH3 (2,2)/(1,1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H2CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H2CO trace turbulence to a higher degree than NH3 (2,2)/(1,1) in the massive clumps. The non-thermal velocity dispersions of para-H2CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions.

Accepted for publication in A&A

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• Gravitational collapse and accretion flows in the hub filament system G323.46-0.08
• Evidence for dense gas heated by the explosion in Orion KL
• Connecting the Cosmic Star Formation Rate with the Local Star Formation
• Submillimeter observations of molecular gas interacting with the supernova remnant W28
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde V. The massive filament DR21
• Cloud-cloud collision and star formation in G013.313+0.193
• Inadequate turbulent support in low-metallicity molecular clouds
• The ALMA Survey of 70 $\mu$m Dark High-mass Clumps in Early Stages (ASHES). XII. Unanchored Forked Stream in the Propagating Path of a Protostellar Outflow
• Molecular Clouds at the Edge of the Galaxy I. Variation of CO J=2-1/1-0 Line Ratio
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN): III. ${}^{13}$CO/C${}^{18}$O ratio variations across the M51 galaxy
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations