The relation of H2CO,12CO, and13CO in molecular clouds

Tang, Xindi; Esimbek, Jarken; Zhou, Jian; Wu, Gang; Ji, Wei; Okoh, Daniel

doi:10.1051/0004-6361/201219809

Cited by 24 publications

(63 citation statements)

References 19 publications

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“…This similarity may indicate that the H 2 CO line exist in the similar regions as the 13 CO does, which was considered to trace a larger scale than the NH 3 dose and to be broader than NH 3 line because of turbulence within that larger scale (Wienen et al 2012). This also agrees with the spatial distribution relation between H 2 CO and 13 CO observed in Tang et al (2013).…”

Section: Line-center Velocity and Line Widthsupporting

confidence: 78%

“…So a higher T C may not necessarily increase the absorption even without the disturbance from column density. Complicated relations between T L and T C were also reported by Zhang et al (2012) and Tang et al (2014). Their results show that there is a certain correlation between T L and T C , but with considerable scatter.…”

Section: Influence Of Extinction and Continuum Emissionsupporting

confidence: 53%

“…This suggests that the H 2 CO absorption associates well with the dense region of the molecular clouds. Comparative studies of the H 2 CO and 12 CO showed that the 4.8-GHz H 2 CO absorption line is similar to the 12 CO, tracing the lower density region of the molecular cloud (Ridge et al 2006;Zhang et al 2012;Tang et al 2013). This may indicate that the H 2 CO absorption line can still probe the molecular cloud well, although it is believed sometimes to be dominated by background continuum radiation.…”

Section: Influence Of Extinction and Continuum Emissionmentioning

confidence: 86%

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H2CO and H110α observations towards NH3 sources

Yuan

Esimbek

Zhou

et al. 2014

Astrophys Space Sci

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We observed the H 2 CO (1 10 − 1 11 ) absorption lines and H 110α radio recombination lines (RRL) toward 180 NH 3 sources using the Nanshan 25-m radio telescope. In our observation, 138 sources were found to have H 2 CO lines and 36 have H 110α RRLs. Among the 138 detected H 2 CO sources, 38 sources were first detected. The detection rates of H 2 CO have a better correlation with extinction than with background continuum radiation. Line center velocities of H 2 CO and NH 3 agree well. The line width ratios of H 2 CO and NH 3 are generally larger than unite and are similar to that of 13 CO. The correlation between column densities of H 2 CO and extinction is better than that between NH 3 and extinction. These line width relation and column density relation indicate H 2 CO is distributed on a larger scale than that of NH 3 and be in similar to the regions of 13 CO. Abundance ratios between NH 3 and H 2 CO were found to be different in local clouds and other clouds.

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Section: Line-center Velocity and Line Widthsupporting

confidence: 78%

Section: Influence Of Extinction and Continuum Emissionsupporting

confidence: 53%

Section: Influence Of Extinction and Continuum Emissionmentioning

confidence: 86%

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H2CO and H110α observations towards NH3 sources

Yuan

Esimbek

Zhou

et al. 2014

Astrophys Space Sci

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“…A few authors (Tang et al 2009(Tang et al , 2013aZhang et al 2014) have measured dust polarization to get the field direction in W51e2. Etoka et al (2012) used OH masers to measure the field strength, obtaining 2-7 mG, which likely come from high-density (~-n 10 10 67 -cm 3 ) gas (Fish et al 2003).K o c he ta l .…”

Section: What About Magnetic Fields?mentioning

confidence: 99%

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

Ginsburg

Goddi

Kruijssen

et al. 2017

ApJ

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Thermal Feedback in the High-mass Star-and Cluster-forming Region W51http://researchonline.ljmu.ac.uk/7346/ Article LJMU has developed LJMU Research Online for users to access the research output of the University more effectively. Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Users may download and/or print one copy of any article(s) in LJMU Research Online to facilitate their private study or for non-commercial research. You may not engage in further distribution of the material or use it for any profit-making activities or any commercial gain.The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription. LJMU Research OnlineThermal Feedback in the High-mass Star-and Cluster-forming Region W51 Abstract High-mass stars have generally been assumed to accrete most of their mass while already contracted onto the main sequence, but this hypothesis has not been observationally tested. We present ALMA observations of a3 1.5 pc area in the W51 high-mass star-forming complex. We identify dust continuum sources and measure the gas and dust temperature through both rotational diagram modeling of CHO H 3 and brightness-temperature-based limits. The observed region contains three high-mass YSOs that appear to be at the earliest stages of their formation, with no signs of ionizing radiation from their central sources. The data reveal high gas and dust temperatures ( > T 100 K) extending out to about 5000 au from each of these sources. There are no clear signs of disks or rotating structures down to our 1000 au resolution. The extended warm gas provides evidence that, during the process of forming, these high-mass stars heat a large volume and correspondingly large mass of gas in their surroundings, inhibiting fragmentation and therefore keeping a large reservoir available to feed from. By contrast, the more mature massive stars that illuminate compact H II regions have little effect on their surrounding dense gas, suggesting that these main-sequence stars have completed most or all of their accretion. The high luminosity of the massive protostars ( > L 10 4  L ), combined with a lack of centimeter continuum emission from these sources, implies that they are not on the main sequence while they accrete the majority of their mass; instead, they may be bloated and cool.

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“…Formaldehyde (H 2 CO) is a ubiquitous molecule in the Galactic interstellar medium (ISM) of our and external galaxies (Downes et al 1980;Cohen & Few 1981;Bieging et al 1982;Cohen et al 1983;Baan et al 1986Baan et al , 1990Baan et al , 1993Henkel et al 1991;Zylka et al 1992;Hüttemeister et al 1997;Heikkilä et al 1999;Wang et al 2004Wang et al , 2009Mangum et al 2008;Zhang et al 2012;Mangum et al 2013b;Ao et al 2013;Tang et al 2013;Ginsburg et al 2015Ginsburg et al , 2016Guo et al 2016). H 2 CO is thought to be formed on the surface of dust grains by successive hydrogenation of CO (Watanabe & Kouchi 2002;Woon 2002;Hidaka et al 2004): CO → HCO → H 2 CO. Variations of the fractional abundance of H 2 CO do not exceed one order of magnitude.…”

Section: Introductionmentioning

confidence: 99%

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

Tang

Henkel

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.

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The relation of H₂CO,¹²CO, and¹³CO in molecular clouds

Cited by 24 publications

References 19 publications

H2CO and H110α observations towards NH3 sources

H2CO and H110α observations towards NH3 sources

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

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

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