Molecular abundances in the high-latitude molecular clouds

1988 ◽  
Vol 326 ◽  
pp. 909 ◽  
Author(s):  
Loris Magnani ◽  
Leo Blitz ◽  
Jan G. A. Wouterloot
Keyword(s):  
High Latitude ◽  
Molecular Clouds ◽  
Molecular Abundances

scholarly journals Dense Knots in High Latitude Molecular Clouds

1992 ◽  
Vol 150 ◽  
pp. 477-482
Author(s):  
Leo Blitz
Keyword(s):  
High Latitude ◽  
Molecular Clouds ◽  
Electron Excitation ◽  
High Density ◽  
Current Debate ◽  
Low Mass ◽  
Molecular Abundances

The high latitude molecular clouds are discussed in the context of the formation of very low mass condensations: protojupiters. The ability to identify such objects is intimately tied to the resolution of the current debate concerning the density of the condensations inferred from observations of high density tracers. At the heart of the debate is whether inclusion of electron excitation plays an important role in the determination of column densities. A brief review of molecular abundances shows that with the possible exception of H2CO, the molecular abundances in the high latitude molecular clouds are not abnormal.

scholarly journals HIGH-LATITUDE, TRANSLUSCENT MOLECULAR CLOUDS AS PROBES OF LOCAL COSMIC RAYS

2015 ◽  
Vol 805 (1) ◽  
pp. 50 ◽  
Author(s):  
Ryan D. Abrahams ◽  
Timothy A. D. Paglione
Keyword(s):  
Cosmic Rays ◽  
High Latitude ◽  
Molecular Clouds

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

Dense gas in high-latitude molecular clouds

1995 ◽  
Vol 441 ◽  
pp. 244 ◽  
Author(s):  
William T. Reach ◽  
Marc W. Pound ◽  
David J. Wilner ◽  
Youngung Lee
Keyword(s):  
High Latitude ◽  
Molecular Clouds ◽  
Dense Gas

Infrared cirrus and high-latitude molecular clouds

1986 ◽  
Vol 306 ◽  
pp. L101 ◽  
Author(s):  
Janet L. Weiland ◽  
Leo Blitz ◽  
Eli Dwek ◽  
M. G. Hauser ◽  
Loris Magnani ◽  
...  
Keyword(s):  
High Latitude ◽  
Molecular Clouds

Chemical Abundances and Isotope Ratios in Molecular Clouds

1996 ◽  
Vol 13 (2) ◽  
pp. 202-203
Author(s):  
M. R. Hunt
Keyword(s):  
Observational Data ◽  
Molecular Clouds ◽  
Isotope Ratios ◽  
Magellanic Clouds ◽  
Chemical Abundances ◽  
Millimetre Wave ◽  
The Galaxy ◽  
Molecular Abundances

AbstractA program to observe millimetre-wave molecular transitions in a number of southern-sky molecular clouds is under way. Molecular clouds in both the Galaxy and the Magellanic Clouds are included in the sample. The aim of the program is to build a body of observational data which can be used to derive molecular abundances in southern-sky molecular clouds.

scholarly journals Dark molecular gas in Pegasus–Pisces

2019 ◽  
Vol 486 (2) ◽  
pp. 2281-2289
Author(s):  
Emmanuel Donate ◽  
Samantha Blair ◽  
Zachary Chilton ◽  
Codie Gladney ◽  
Jeremy W Gordon ◽  
...  
Keyword(s):  
Molecular Mass ◽  
Spatial Resolution ◽  
High Latitude ◽  
Molecular Clouds ◽  
Large Region ◽  
Molecular Gas ◽  
Optimal Estimate

Abstract We examine the molecular content of a large region (∼2200 square degrees) in Pegasus–Pisces with an estimated dark molecular gas fraction of 59 per cent. Using the extensive CO(1-0) Southern Galactic hemisphere, high-latitude survey by Magnani et al. (2000), we re-examined the CO-detectable mass estimates for the region. By averaging all the CO spectra in subsections ranging in size from 3° × 3° to 15° × 15°, we decreased the rms of the averaged CO spectra by factors of 3–10, effectively trading spatial resolution for sensitivity. With the new spectra, we are able to make estimates of the CO-detectable mass as a function of sensitivity. Using the optimal estimate, the CO-detectable mass increases from 2200 to 4000 M⊙, thereby decreasing the dark molecular gas fraction in the region to 0.24. CO(1–0) observations with rms values in the 20–30 mK range can nearly double the molecular mass in regions with diffuse and translucent molecular clouds.

scholarly journals Reproducing the CO-to-H2 conversion factor in cosmological simulations of Milky-Way-mass galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. 837-850
Author(s):  
Laura C Keating ◽  
Alexander J Richings ◽  
Norman Murray ◽  
Claude-André Faucher-Giguère ◽  
Philip F Hopkins ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Milky Way ◽  
Conversion Factor ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Giant Molecular Clouds ◽  
Post Processing ◽  
Subgrid Model ◽  
Local Sources ◽  
Molecular Abundances

ABSTRACT We present models of CO(1–0) emission from Milky-Way-mass galaxies at redshift zero in the FIRE-2 cosmological zoom-in simulations. We calculate the molecular abundances by post-processing the simulations with an equilibrium chemistry solver while accounting for the effects of local sources, and determine the emergent CO(1–0) emission using a line radiative transfer code. We find that the results depend strongly on the shielding length assumed, which, in our models, sets the attenuation of the incident UV radiation field. At the resolution of these simulations, commonly used choices for the shielding length, such as the Jeans length, result in CO abundances that are too high at a given H2 abundance. We find that a model with a distribution of shielding lengths, which has a median shielding length of ∼3 pc in cold gas (T < 300 K) for both CO and H2, is able to reproduce both the observed CO(1–0) luminosity and inferred CO-to-H2 conversion factor at a given star formation rate compared with observations. We suggest that this short shielding length can be thought of as a subgrid model, which controls the amount of radiation that penetrates giant molecular clouds.

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