Formaldehyde as a probe of physical conditions in dense molecular clouds

Mangum, J. G.; Wootten, Alwyn

doi:10.1086/191841

Cited by 209 publications

(262 citation statements)

References 78 publications

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“…Ratios of lines from different J−states tend to be density tracers (left panels), while ratios of lines from the same J−state but different K−states are mostly temperature probes (right panels). The lines of H 2 CO are often quite strong, making this molecule a favourite tracer of temperature and density (Mangum & Wootten 1993). Other asymmetric molecules have also been used, such as H 2 CS (Blake et al 1994) and CH 3 OH (Leurini et al 2004) although abundance variations from source to source or even within sources often complicate the interpretation (Johnstone et al 2003).…”

Section: Appendix C: Diagnostic Plots Of Molecular Line Ratiosmentioning

confidence: 99%

A computer program for fast non-LTE analysis of interstellar line spectra

Tak¹,

Black²,

Schöier³

et al. 2007

A&A

1,383

841

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Aims. The large quantity and high quality of modern radio and infrared line observations require efficient modeling techniques to infer physical and chemical parameters such as temperature, density, and molecular abundances. Methods. We present a computer program to calculate the intensities of atomic and molecular lines produced in a uniform medium, based on statistical equilibrium calculations involving collisional and radiative processes and including radiation from background sources. Optical depth effects are treated with an escape probability method. The program is available on the World Wide Web at http://www.sron.rug.nl/∼vdtak/radex/index.shtml. The program makes use of molecular data files maintained in the Leiden Atomic and Molecular Database (LAMDA), which will continue to be improved and expanded. Results. The performance of the program is compared with more approximate and with more sophisticated methods. An Appendix provides diagnostic plots to estimate physical parameters from line intensity ratios of commonly observed molecules. Conclusions. This program should form an important tool in analyzing observations from current and future radio and infrared telescopes.

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Section: Appendix C: Diagnostic Plots Of Molecular Line Ratiosmentioning

confidence: 99%

A computer program for fast non-LTE analysis of interstellar line spectra

Tak¹,

Black²,

Schöier³

et al. 2007

A&A

1,383

841

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“…According to Mangum & Wootten (1993), these two transitions are enough to determine temperatures, therefore we did not use the third detected transition, H 2 CO 3 2,1 −2 2,0 , for the temperature analysis.…”

Section: Formaldehydementioning

confidence: 99%

“…Formaldehyde (H 2 CO), one of the first polyatomic molecules discovered in space, has proven its usefulness in deriving the physical properties of the interstellar gas (e.g., Mangum & Wootten 1993;Jansen et al 1994Jansen et al , 1995Mühle et al 2007;Watanabe & Mitchell 2008). In particular, H 2 CO allows one to A51, page 6 of 17 estimate the kinetic temperature and the spatial density of starforming regions.…”

Section: Applying H 2 Co Line Ratiosmentioning

confidence: 99%

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Fragmentation in the massive star-forming region IRAS 19410+2336

Rodón

Beuther

Schilke

2012

A&A

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Context. The core mass functions (CMFs) of low-mass star-forming regions are found to resemble the shape of the initial mass function (IMF). A similar result is observed for the dust clumps in high-mass star-forming regions, although on spatial scales of clusters that do not resolve the substructure that is found in these massive clumps. The region IRAS 19410+2336 is one exception, having been observed on spatial scales on the order of ∼2500 AU, which are sufficient to resolve the clump substructure into individual cores. Aims. We investigate the protostellar content of IRAS 19410+2336 at high spatial resolution at 1.4 mm, determining the temperature structure of the region and deriving its CMF. Methods. The massive star-forming region IRAS 19410+2336 was mapped with the PdBI (BCD configurations) at 1.4 mm and 3 mm in the continuum and several transitions of formaldehyde (H 2 CO) and methyl cyanide (CH 3 CN). The H 2 CO transitions were also observed with the IRAM 30 m Telescope. Results. We detect 26 continuum sources at 1.4 mm with a spatial resolution as low as ∼2200 AU, several of them with counterparts at near-and mid-infrared wavelengths, distributed in two (proto)clusters. With the PdBI CH 3 CN and PdBI/IRAM 30 m H 2 CO emission, we derive the temperature structure of the region, ranging from 35 K to 90 K. Using these temperatures, we calculate the core masses of the detected sources, ranging from ∼0.7 M to ∼8 M . These masses are strongly affected by the spatial filtering of the interferometer, which removes a common envelope with ∼90% of the single-dish flux. Considering only the detected dense cores and accounting for binning effects as well as cumulative distributions, we derive a CMF, with a power-law index β = −2.3 ± 0.2. We resolve the Jeans length of the (proto)clusters by one order of magnitude, and only find a small velocity dispersion between the different subsources. Conclusions. Since we cannot unambiguously differentiate between protostellar and prestellar cores, the derived CMF is not prestellar. Furthermore, because of the large fraction of missing flux, we cannot establish a firm link between the CMF and the IMF. This implies that future high-mass CMF studies will need to complement the interferometer continuum data with the short spacing information, a task suitable for ALMA. We note that the method of extracting temperatures using H 2 CO lines becomes less applicable when reaching the dense core scales of the interferometric observations because most of the H 2 CO appears to originate in the envelope structure.

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“…The 3 22 → 2 21 /3 03 → 2 02 line ratio is sensitive to temperature (e.g., van Dishoeck et al 1993;Mangum & Wootten 1993), especially in the regime of 50−200 K. For L1448-C, the interferometer data give a ratio of 0.68 ± 0.39 indicating the presence of hot gas with T > ∼ 70 K. For comparison, the single-dish line ratio is 0.12 ± 0.04 (Maret et al 2004), corresponding to T ≈ 20−30 K. Optical depth effects and abundance variations with radius (i.e., temperature) can affect this ratio, however, so that more detailed radiative transfer modeling is needed for a proper interpretation.…”

Section: L1448-cmentioning

confidence: 99%

On the origin of H$_\mathsf{2}$CO abundance enhancements in low-mass protostars

Schöier

Jørgensen

Dishoeck

et al. 2004

A&A

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Abstract.High angular resolution H 2 CO 218 GHz line observations have been carried out toward the low-mass protostars IRAS 16293-2422 and L1448-C using the Owens Valley Millimeter Array at ∼2 resolution. Simultaneous 1.37 mm continuum data reveal extended emission which is compared with that predicted by model envelopes constrained from single-dish data. For L1448-C the model density structure works well down to the 400 AU scale to which the interferometer is sensitive. For IRAS 16293-2422, a known proto-binary object, the interferometer observations indicate that the binary has cleared much of the material in the inner part of the envelope, out to the binary separation of ∼800 AU. For both sources there is excess unresolved compact emission centered on the sources, most likely due to accretion disks < ∼ 200 AU in size with masses of IRAS 16293-2422). The H 2 CO data for both sources are dominated by emission from gas close to the positions of the continuum peaks. The morphology and velocity structure of the H 2 CO array data have been used to investigate whether the abundance enhancements inferred from single-dish modelling are due to thermal evaporation of ices or due to liberation of the ice mantles by shocks in the inner envelope. For IRAS 16293-2422 the H 2 CO interferometer observations indicate the presence of rotation roughly perpendicular to the large scale CO outflow. The H 2 CO distribution differs from that of C 18 O, with C 18 O emission peaking near MM1 and H 2 CO stronger near MM2. For L1448-C, the region of enhanced H 2 CO emission extends over a much larger scale >1 than the radius of 50−100 K (0. 6−0. 15) where thermal evaporation can occur. The red-blue asymmetry of the emission is consistent with the outflow; however the velocities are significantly lower. The H 2 CO 3 22 −2 21 /3 03 −2 02 flux ratio derived from the interferometer data is significantly higher than that found from single-dish observations for both objects, suggesting that the compact emission arises from warmer gas. Detailed radiative transfer modeling shows, however, that the ratio is affected by abundance gradients and optical depth in the 3 03 −2 02 line. It is concluded that a constant H 2 CO abundance throughout the envelope cannot fit the interferometer data of the two H 2 CO lines simultaneously on the longest and shortest baselines. A scenario in which the H 2 CO abundance drops in the cold dense part of the envelope where CO is frozen out but is undepleted in the outermost region provides good fits to the single-dish and interferometer data on short baselines for both sources. Emission on the longer baselines is best reproduced if the H 2 CO abundance is increased by about an order of magnitude from ∼10 −10 to ∼10 −9 in the inner parts of the envelope due to thermal evaporation when the temperature exceeds ∼50 K. The presence of additional H 2 CO abundance jumps in the innermost hot core region or in the disk cannot be firmly established, however, with the present sensitivity and resolution. Other scenarios, includi...

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Formaldehyde as a probe of physical conditions in dense molecular clouds

Cited by 209 publications

References 78 publications

A computer program for fast non-LTE analysis of interstellar line spectra

A computer program for fast non-LTE analysis of interstellar line spectra

Fragmentation in the massive star-forming region IRAS 19410+2336

On the origin of H$_\mathsf{2}$CO abundance enhancements in low-mass protostars

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