The distribution of cosmic-ray ionization rates in diffuse molecular clouds as probed by H
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Owing to its simple chemistry, H is widely regarded as the most reliable tracer of the cosmic-ray ionization rate in diffuse interstellar clouds. At present, H observations have been made in over 50 sight lines that probe the diffuse interstellar medium (ISM) throughout the Galaxy. This small survey presents the opportunity to investigate the distribution of cosmic-ray ionization rates in the ISM, as well as any correlations between the ionization rate and line-of-sight properties. Some of the highest inferred ionization rates are about 25 times larger than the lowest upper limits, suggesting variations in the underlying low-energy cosmic-ray flux across the Galaxy. Most likely, such variations are caused predominantly by the distance between an observed cloud and the nearest site of particle acceleration.

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The Determination of Electron Abundances in Interstellar Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900072843 ◽

1980 ◽

Vol 87 ◽

pp. 339-340

Author(s):

Alwyn Wootten ◽

Ronald Snell ◽

A. E. Glassgold

Keyword(s):

Gas Phase ◽

Molecular Clouds ◽

Cosmic Ray ◽

Ionization Rate ◽

Interstellar Clouds ◽

Ion Molecule Reactions ◽

Upper Limits ◽

Gas Phase Ion ◽

Existing Data

A new method for estimating electron fractions in shielded molecular clouds is proposed on the basis of gas phase ion-molecule reactions which involves measuring the quantity . Applied to existing data, it yields upper limits to Xe in the range from 10−8 to 10−7 for a variety of clouds, warm as well as cool. An upper bound to the cosmic ray ionization rate is also obtained.

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Molecular Clouds and Star Formation at Large R

Symposium - International Astronomical Union ◽

10.1017/s0074180900088987 ◽

1991 ◽

Vol 144 ◽

pp. 121-130

Author(s):

J. Brand ◽

J.G.A. Wouterloot

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Density Wave ◽

Cosmic Ray ◽

Volume Density ◽

Kinetic Temperature ◽

Galactocentric Distance ◽

The Galaxy ◽

The Mean ◽

Cosmic Ray Flux

In the outer Galaxy (defined here as those parts of our system with galactocentric radii R>R0) the HI gas density (Wouterloot et al., 1990), the cosmic ray flux (Bloemen et al, 1984) and the metallicity (Shaver et al., 1983) are lower than in the inner parts. Also, the effect of a spiral density wave is much reduced in the outer parts of the Galaxy due to corotation. This changing environment might be expected to have its influence on the formation of molecular clouds and on star formation within them. In fact, some differences with respect to the inner Galaxy have been found: the ratio of HI to H2 surface density is increasing from about 5 near the Sun to about 100 at R≈20kpc (Wouterloot et al., 1990). Because of the “flaring” of the gaseous disk, the scale height of both the atomic and the molecular gas increases by about a factor of 3 between R0 and 2R0 (Wouterloot et al., 1990), so the mean volume density of both constituents decreases even more rapidly than their surface densities. The size of HII regions decreases significantly with increasing galactocentric distance (Fich and Blitz, 1984), probably due to the fact that outer Galaxy clouds are less massive (see section 3.3), and therefore form fewer O-type stars than their inner Galaxy counter parts. There are indications that the cloud kinetic temperature is lower by a few degrees (Mead and Kutner, 1988), although it is not clear to what extent this is caused by beam dilution.

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On the Cosmic Ray-Induced Ionization Rate in Molecular Clouds

ISRN Astronomy and Astrophysics ◽

10.5402/2011/905015 ◽

2011 ◽

Vol 2011 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Ararat G. Yeghikyan

Keyword(s):

Molecular Clouds ◽

Column Density ◽

Cosmic Ray ◽

Ionization Rate ◽

Electronic Interaction ◽

Absorbing Medium ◽

Be Star ◽

Good Agreement ◽

Ionization Rates

The transformation of the energy dependence of the cosmic ray proton flux in the keV to GeV region is investigated theoretically when penetrating inside molecular clouds ( mag). The computations suggest that energy losses of the cosmic ray particles by interaction with the matter of the molecular cloud are principally caused by the inelastic (electronic) interaction potential; the transformed energy distribution of energetic protons is determined mainly by the column density of the absorbing medium. A cutoff of the cosmic ray spectrum inside clouds by their magnetic fields is also phenomenologically taken into account. This procedure allows a determination of environment-dependent ionization rates of molecular clouds. The theoretically predicted ionization rates are in good agreement with those derived from astronomical observations of absorption lines in the spectrum of the cloud connected with the Herbig Be star LkH 101.

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The EDIBLES survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833039 ◽

2019 ◽

Vol 622 ◽

pp. A31 ◽

Cited By ~ 5

Author(s):

Xavier L. Bacalla ◽

Harold Linnartz ◽

Nick L. J. Cox ◽

Jan Cami ◽

Evelyne Roueff ◽

...

Keyword(s):

Band System ◽

Cosmic Ray ◽

Far Infrared ◽

Ionization Rate ◽

Electronic Band ◽

Interstellar Clouds ◽

Near Ultraviolet ◽

Diffuse Interstellar Bands ◽

Range Of Values ◽

Ionization Rates

We report cosmic ray ionization rates toward ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between two and ten individual rotational lines of OH+ have been detected in its (0,0) and (1,0) A3Π − X3Σ− electronic band system. This allows constraining of OH+ column densities toward different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the primary cosmic ray ionization rate ζp in the targeted diffuse interstellar clouds. For the ten selected targets, we obtain a range of values for ζp equal to (3.9–16.4) × 10−16 s−1. These values are higher than the numbers derived in previous detections of interstellar OH+ in the far-infrared/submillimeter-wave regions and in other near-ultraviolet studies. This difference is a result of using new OH+ oscillator strength values and a more complete picture of all relevant OH+ formation and destruction routes (including the effect of proton recombinations on PAHs), and the relatively high N(OH+) seen toward those ten targets.

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Towards an anagraphical picture of high-energy Galactic neutrinos

EPJ Web of Conferences ◽

10.1051/epjconf/201920901003 ◽

2019 ◽

Vol 209 ◽

pp. 01003

Author(s):

Antonio Marinelli ◽

Dario Grasso ◽

Sofia Ventura

Keyword(s):

Short Duration ◽

Molecular Clouds ◽

Supernova Remnants ◽

Cosmic Ray ◽

High Energy ◽

The Other ◽

Molecular Gas ◽

High Energy Neutrino ◽

Neutrino Telescopes ◽

Upper Limits

The TeV/PeV neutrino emission from our Galaxy is related to the distribution of cosmic-ray accelerators, their maximal energy of injection as well as the propagation of injected particles and their interaction with molecular gas. In the last years Interesting upper limits on the diffuse hadronic emission from the whole Galaxy, massive molecular clouds and Fermi Bubbles were set by the IceCube and ANTARES as well as HAWC and Fermi-LAT observations. On the other hand no evidence of Galactic point-like excess has been observed up to now by high-energy neutrino telescopes. This result can be related to the short duration of the PeV hadronic activity of the sources responsible for the acceleration of primary protons, possibly including supernova remnants. All these aspects will be discussed in this work.

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The Mass Spectrum of Interstellar Clouds

International Astronomical Union Colloquium ◽

10.1017/s0252921100024325 ◽

1989 ◽

Vol 120 ◽

pp. 511-517

Author(s):

John M. Dickey ◽

R. W. Garwood

Keyword(s):

Cross Sections ◽

Molecular Clouds ◽

Column Density ◽

Unit Volume ◽

Empirical Relationship ◽

Line Of Sight ◽

Interstellar Clouds ◽

Absorption Studies ◽

Low Latitudes ◽

Diffuse Clouds

AbstractThe abundance of 21-cm absorption lines seen in surveys at high latitudes can be translated into a line of sight abundance of clouds vs. column density using an empirical relationship between temperature and optical depth. As VLA surveys of 21-cm absorption at low latitudes are now becoming available, it is possible to study the variation of this function with galactic radius. It is interesting to compare the abundance of these diffuse atomic clouds (with temperatures of 50 to 100 K and masses of 1 to 10 M⊙) to the abundance of molecular clouds. To do the latter we must make assumptions about cloud cross-sections in order to convert the line of sight abundance of diffuse clouds into a number per unit volume, and to convert from cloud column density to mass. The spectrum of diffuse clouds matches fairly well the spectrum of molecular clouds, although observationally there is a gap of several orders of magnitude in cloud mass. Optical absorption studies also agree well with the 21-cm results for clouds of column density a few times 1020 M⊙.

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Measurements of Isotopic Abundances in Interstellar Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900072946 ◽

1980 ◽

Vol 87 ◽

pp. 397-404 ◽

Cited By ~ 3

Author(s):

Arno A. Penzias

Keyword(s):

Molecular Clouds ◽

General Framework ◽

Galactic Center ◽

Galactic Plane ◽

Giant Molecular Clouds ◽

Interstellar Clouds ◽

The Galaxy ◽

Isotopic Abundances ◽

Si Isotopes

While an examination of the available data reveals some seemingly contradictory results, a general framework having the following outlines can be put forward:1. With the exception of the two galactic center sources SgrA and SgrB, the relative isotopic abundances exhibited by the giant molecular clouds in our Galaxy exhibit few, if any, significant variations from the values obtained by averaging the data from all these sources.2. The 13C/12C and 14N/15N abundance ratios are ∼130% and ∼150%, respectively, of their terrestrial values throughout the galactic plane and somewhat higher, ∼300%, near the galactic center.3. The 16O/18O and 17O/18O abundance ratios are ∼130% and ∼160%, respectively, of their terrestrial values throughout the Galaxy, although the former may be somewhat lower near the galactic center.4. The S and Si isotopes have generally terrestrial abundances.

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