HYDROXYL AS A TRACER OF H<sub>2</sub>IN THE ENVELOPE OF MBM40

Cotten, David L.; Magnani, L.; Wennerstrom, Elizabeth; Douglas, K. A.; Onello, Joseph S.

doi:10.1088/0004-6256/144/6/163

Cited by 27 publications

(27 citation statements)

References 34 publications

(53 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Using this method yields molecular masses of 9.6 ± 5, 12 ± 6, and 10 ± 5 M for the core, envelope, and periphery regions, respectively. These masses are about a factor of 2 greater than those determined from OH observations by Cotten et al (2012) who estimated molecular masses of 3.8 ± 0.86, 7.6 ± 2.5, and 5.2 ± 6.3 M for the core, envelope, and periphery regions, respectively. The differences in the two estimates depend directly on the values of X CO and the OH/H 2 abundance that are used in each derivation of the mass for each region.…”

Section: Determination From X Cocontrasting

confidence: 51%

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

Cotten

Magnani

2013

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

We made CO(1-0) observations of 103 lines of sight in the core and envelope of the highlatitude cloud MBM 40 to determine how the CO-H 2 conversion factor (X CO ) varies throughout the cloud. Calibrating X CO with CH data at similar resolution (1 for CO, 1.5 for CH) yields values of X CO ranging from 0.6 × 10 20 to 3.3 × 10 20 cm −2 [K km s −1 ] −1 with an average of 1.3 × 10 20 cm −2 [K km s −1 ] −1 . Given that the cloud has a peak reddening of 0.24 mag, it should be classed as a diffuse rather than a translucent molecular cloud. The mass obtained from the CO data and our values of X CO is 9.6 M for the core, 12 M for the envelope, and 10 M for the periphery of the cloud. A third of the molecular mass of the cloud is found in a region with E(B-V) < 0.12 mag. With these mass estimates, we determine that the cloud is not gravitationally bound.

show abstract

Section: Determination From X Cocontrasting

confidence: 51%

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

Cotten

Magnani

2013

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

show abstract

“…More recently, other tracers have also been used to study CO-dark gas, in particular the hydroxyl radical OH (e.g. Crutcher et al 1993;Barriault et al 2010;Cotten et al 2012;Allen et al 2015;Li et al 2015Li et al , 2018aEbisawa et al 2019). In a sub-pc resolution observation of OH, Xu et al (2016) find CO-dark gas fractions varying from 80% to 20% across the boundary of the Taurus molecular cloud.…”

Section: Introductionmentioning

confidence: 99%

SILCC-Zoom: H2 and CO-dark gas in molecular clouds – the impact of feedback and magnetic fields

Seifried

Haid

Walch

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We analyse the CO-dark molecular gas content of simulated molecular clouds from the SILCC-Zoom project. The simulations reach a resolution of 0.1 pc and include H 2 and CO formation, radiative stellar feedback and magnetic fields. CO-dark gas is found in regions with local visual extinctions A V,3D ∼ 0.2 -1.5, number densities of 3 -300 cm −3 and gas temperatures of few 10 K -100 K. CO-bright gas is found at number densities above 300 cm −3 and temperatures below 50 K. The CO-dark gas fractions range from 40% to 95% and scale inversely with the amount of well-shielded gas (A V,3D 1.5), which is smaller in magnetised molecular clouds. We show that the density, chemical abundances and A V,3D along a given line-of-sight cannot be properly determined from projected quantities. As an example, we show that pixels with a projected visual extinction of A V,2D ≃ 2.5 -5 can be both, CO-bright and CO-dark. By producing synthetic CO(1-0) emission maps of the simulations with RADMC-3D, we show that about 15 -65% of the H 2 is in regions with CO(1-0) emission below the detection limit. The simulated clouds have X CO -factors around 1.5 × 10 20 cm −2 (K km s −1 ) −1 with a spread of up to a factor ∼ 4, implying a similar uncertainty in the derived total H 2 masses and even worse results for individual pixels. Based on our results, we suggest a new approach to determine the H 2 mass, which relies on the availability of CO(1-0) emission and A V,2D maps. It reduces the uncertainty of the clouds' overall H 2 mass to a factor of 1.8 and for individual pixels, i.e. on sub-pc scales, to a factor of 3.

show abstract

“…The rotational transitions of the hydroxyl radical (OH) are unique probes of diffuse and dense interstellar clouds, late-type stars, and external galaxies (e.g. Harju, Winnberg & Wouterloot 2000;Goicoechea et al 2011;Cotten et al 2012;Wampfler et al 2013;Ebisawa et al 2015). Indeed, observations of OH provide critical constraints on both the density and temperature of the media.…”

Section: Introductionmentioning

confidence: 99%

The excitation of OH by H2 revisited – II. Hyperfine resolved rate coefficients

Kłos

Dagdigian

Alexander

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Observations of hyperfine resolved transitions of the hydroxyl radical (OH) are unique probes of the physical conditions in molecular clouds. In particular, hyperfine intensities can be used as an effective thermometer over a wide range of molecular densities. Accurate modelling of the OH emission spectra requires the calculation of collisional rate coefficients for the excitation of OH by H2, the most abundant collisional partner in the molecular clouds. Here, we determine hyperfine resolved rate coefficients for the excitation of OH by H2 using a recently developed highly accurate potential energy surface. State-to-state rate coefficients between the lower hyperfine levels were calculated using recoupling techniques for temperature ranging from 10 to 150 K. Significant differences were found with the earlier values currently used in astrophysical models, the new rate coefficients being larger than the previous ones. Finally, we compute the excitation of the OH radical in cold molecular clouds and star-forming regions. The new rate coefficients were found to increase the hyperfine intensities by a factor of ∼1–2. Consequently, we recommend using this new set of data in any astrophysical model of OH excitation.

show abstract

HYDROXYL AS A TRACER OF H₂IN THE ENVELOPE OF MBM40

Cited by 27 publications

References 34 publications

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

SILCC-Zoom: H2 and CO-dark gas in molecular clouds – the impact of feedback and magnetic fields

The excitation of OH by H2 revisited – II. Hyperfine resolved rate coefficients

Contact Info

Product

Resources

About

HYDROXYL AS A TRACER OF H2IN THE ENVELOPE OF MBM40

Cited by 27 publications

References 34 publications

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

A high-resolution study of the CO-H2 conversion factor in the diffuse cloud MBM 40

SILCC-Zoom: H2 and CO-dark gas in molecular clouds – the impact of feedback and magnetic fields

The excitation of OH by H2 revisited – II. Hyperfine resolved rate coefficients

Contact Info

Product

Resources

About

HYDROXYL AS A TRACER OF H₂IN THE ENVELOPE OF MBM40