SIMBAD references

2017A&A...600A..16T - Astronomy and Astrophysics, volume 600A, 16-16 (2017/4-1)

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. II. The Large Magellanic Cloud.


Abstract (from CDS):

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) is the closest star-forming galaxy with a low metallicity and provides an ideal laboratory for studying star formation in such an environment.
Aims. The classical dense molecular gas thermometer NH3 is seldom 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 (JKAKC=303-202, 322-221, and 321-220) of para-H2CO near 218GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12m telescope toward six star-forming regions in the LMC. These data are complemented by C18O 2-1 spectra.
Results. Using non-local thermal equilibrium modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H2CO 321-220/303-202 and para-H2CO 303-202/C18O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H2CO line could be detected, the gas kinetic temperatures derived from the preferred para-H2CO 321-220/303-202 line ratios range from 35 to 63K with an average of 47±5K (errors are unweighted standard deviations of the mean). Spatial densities of the gas derived from the para-H2CO 303-202/C18O 2-1 line ratios yield 0.4-2.9x105cm–3 with an average of 1.5±0.4x105cm–3. Temperatures derived from the para-H2CO 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(H2)>103cm–3) of the LMC. A comparison of kinetic temperatures derived from para-H2CO with those from the dust also shows good agreement. This suggests that the dust and para-H2CO are well mixed in the studied star-forming regions. A comparison of kinetic temperatures derived from para-H2CO 321-220/303-202 and NH3(2, 2)/(1, 1) shows a drastic difference, however. In the star-forming region N159W, the gas temperature derived from the NH3(2, 2)/(1, 1) line ratio is ∼16K (Ott et al., 2010ApJ...710..105O), which is only half the temperature derived from para-H2CO 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 that are not yet irradiated by UV photons, while formaldehyde, less affected by photodissociation, is more widespread and also samples regions that are more exposed to the radiation of young massive stars. A correlation between the gas kinetic temperatures derived from para-H2CO and infrared luminosity, represented by the 250µm flux, suggests that the kinetic temperatures traced by para-H2CO are correlated with the ongoing massive star formation in the LMC.

Abstract Copyright: © ESO, 2017

Journal keyword(s): stars: formation - Magellanic Clouds - ISM: clouds - ISM: molecules - radio lines: ISM - radio lines: ISM

VizieR on-line data: <Available at CDS (J/A+A/600/A16): table1.dat table2.dat table3.dat list.dat fits/*>

Simbad objects: 15

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