Influence of Radiative Pumping on the HD Rotational Level Populations in Diffuse Molecular Clouds of the Interstellar Medium

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

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Symposium Summary: Fragmentation and Star Formation in Molecular Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900199097 ◽

1991 ◽

Vol 147 ◽

pp. 379-386

Author(s):

A. E. Glassgold

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Molecular Clouds ◽

Substantial Progress ◽

Made In ◽

Easy Solution

This Symposium on fragmentation and star formation has dealt with the heart of the study of molecular clouds, which is how they form stars. This problem is one of the most profound and challenging problems in all of astrophysics. The complexity of the interstellar medium adds to its difficulty and we cannot expect a quick and easy solution. Nonetheless, the reports presented at this Symposium indicate that substantial progress is being made in this field.

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Relations Between Star Formation and the Interstellar Medium

Symposium - International Astronomical Union ◽

10.1017/s0074180900128487 ◽

1998 ◽

Vol 179 ◽

pp. 165-171 ◽

Cited By ~ 1

Author(s):

Y. Fukui ◽

Y. Yonekura

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Formation Process ◽

Molecular Clouds ◽

Future Prospects

We review observational results concerning star formation and dense molecular clouds, the interstellar medium most relevant to star-formation process, as well as future prospects.

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First Results from the Submillimeter Wave Astronomy Satellite – H2O and O2 Discoveries

Symposium - International Astronomical Union ◽

10.1017/s0074180900164769 ◽

2000 ◽

Vol 197 ◽

pp. 161-174

Author(s):

Gary J. Melnick

Keyword(s):

Interstellar Medium ◽

Ground State ◽

Molecular Clouds ◽

Submillimeter Wave ◽

Important Species ◽

First Results ◽

One Year

The Submillimeter Wave Astronomy Satellite (SWAS) was successfully launched on 5 December 1998 with the goals of studying: (1) the distribution of oxygen in the interstellar medium; (2) the role of H2O and O2 as gas coolants; and (3) the UV-illuminated surfaces of molecular clouds. To achieve these goals, SWAS is conducting pointed observations of dense (n(H2) > 103 cm–3) molecular clouds throughout our Galaxy in either the ground-state or a low-lying transition of five astrophysically important species: H2O, H218O, O2, CI, and 13CO. SWAS has made great strides in each of these areas of investigation. This paper will summarize our H2O and O2 findings one year into the mission.

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Molecular Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900142238 ◽

1977 ◽

Vol 75 ◽

pp. 37-54 ◽

Cited By ~ 2

Author(s):

P. Thaddeus

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Molecular Clouds ◽

Physical State ◽

Molecular Gas ◽

Spectroscopic Techniques ◽

Low Density ◽

Recombination Line ◽

Interstellar Gas ◽

Impossible Task

To attempt to understand star formation without knowing the physical state of the dense interstellar molecular gas from which stars are made is an almost impossible task. Star formation has developed late as a branch of astrophysics largely for lack of observational data, and in particular, has lagged badly behind the study of the atomic and ionized components of the interstellar gas because spectroscopic techniques which work well at low density have an unfortunate tendency to fail when the density is high. Optical spectroscopy, which has been applied to the interstellar medium for over 70 years, has made little progress in regions of high density because of obscuration, and the same is true a fortiori of spacecraft spectroscopy in the UV; radio 21-cm and recombination line observations, although unhampered by obscuration, are unsatisfactory because the dense condensations are almost entirely molecular in composition.

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Formation, Evolution and Destruction of Possible DIB Carriers: Dirty Molecular Hydrogen Ice Clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313016177 ◽

2013 ◽

Vol 9 (S297) ◽

pp. 381-382

Author(s):

D. K. Lynch ◽

L. S. Bernstein ◽

F. O. Clark

Keyword(s):

Interstellar Medium ◽

Single Molecule ◽

Molecular Hydrogen ◽

Molecular Clouds ◽

Single Layer ◽

Molecular Clusters ◽

Electronic Transitions ◽

Giant Molecular Clouds ◽

Diffuse Interstellar Bands ◽

Optical Photons

AbstractWe suggest that the diffuse interstellar bands (DIBs) are absorption lines arising from electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion (“seed”), embedded in a single-layer shell of H2 molecules (Bernstein et al. 2013). We refer to these clusters as CHCs (Contaminated H2 Clusters). CHCs arise from cm-sized, dirty H2 ice balls, called CHIMPs (Contaminated H2 Ice Macro-Particles), formed in cold, dense, Giant Molecular Clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Absorption by the CHIMP of a UV photon releases CHCs. CHCs produce DIBs when they absorb optical photons. When this occurs, the absorbed photon energy disrupts the CHC.

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