The physics and chemistry of small molecular clouds in the galactic plane. 1: Physical conditions form C(18)O and (13)CO observations

1994 ◽  
Vol 420 ◽  
pp. 661 ◽  
Author(s):  
B. E. Turner
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Physical Conditions ◽  
Co Observations

scholarly journals CO observations of the 30-Doradus region using SEST

1991 ◽  
Vol 148 ◽  
pp. 157-159
Author(s):  
R. S. Booth ◽  
L.E.B. Johansson
Keyword(s):  
Molecular Clouds ◽  
Small Areas ◽  
The Relationship ◽  
Co Observations ◽  
30 Doradus

Using the Swedish-ESO Submillimetre Telescope, we have mapped the CO (1-0) emission in two small areas of the LMC near 30 Dor. Some 20 molecular clouds have been identified and analysed. Cloud masses are calculated assuming virial equilibrium and the relationship between mass and CO luminosity is discussed.

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.

scholarly journals Discovery of the Carina Flare with NANTEN; Evidence for a Supershell That Triggered the Formation of Stars and Massive Molecular Clouds

1999 ◽  
Vol 51 (6) ◽  
pp. 751-764 ◽  
Author(s):  
Yasuo Fukui ◽  
Toshikazu Onishi ◽  
Rihei Abe ◽  
Akiko Kawamura ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Infrared Emission ◽  
High Mass ◽  
Stellar Winds ◽  
Neutral Gas ◽  
Supernova Explosions ◽  
Current Kinetic

Abstract We present extensive observations of the Carina arm region in the 2.6 mm CO (J = 1−0) emission with the NANTEN telescope in Chile. The observations have revealed 120 molecular clouds which are distributed in an area of 283° < l < 293° and 2° .5 < b < 10°. Because of its vertical elongation to the galactic plane, the clouds are named the Carina flare. H I and far-infrared emission show a cavity-like distribution corresponding to the molecular clouds, and soft X-ray emission appears to fill this cavity. It is shown that the Carina flare represents a supershell at a distance of a few kpc that has been produced by about 20 supernova explosions, or equivalent stellar winds of OB stars, over the last ∼ 2×107 yr. The supershell consisting of molecular and atomic neutral gas involves a total mass and kinetic energy of ≳ 3×105M⊙ and ≳ 3×1050 erg, respectively, and the originally injected energy required is about 100-times this current kinetic energy in the shell. It is unique among supershells known previously because of the following aspects: i) it exhibits evidence for the triggered formation of intermediate-to-high-mass stars and massive molecular clouds of 102 − 104M⊙, and ii) the massive molecular clouds formed are located unusually far above the galactic plane at z ∼ 100–500 pc.

scholarly journals CO and the Multiphase ISM

1997 ◽  
Vol 170 ◽  
pp. 25-32
Author(s):  
Christopher F. Mckee
Keyword(s):  
Mach Number ◽  
Magnetic Fields ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Molecular Gas ◽  
Wave Pressure ◽  
Multiphase Structure ◽  
Co Observations

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.

scholarly journals Study of the 13CO/C18O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

2019 ◽  
Vol 36 ◽  
Author(s):  
M. B. Areal ◽  
S. Paron ◽  
M. E. Ortega ◽  
L. Duvidovich
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Abundance Ratio ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Accurate Analysis ◽  
Good Tool ◽  
Dark Cloud ◽  
Average Value ◽  
Far Ultraviolet

Abstract Nowadays, there are several observational studies about the 13CO/C18O abundance ratio ( $X^{13/18}$ ) towards nearby molecular clouds. These works give observational support to the C18O selective photodissociation due to the interaction between the far ultraviolet (FUV) radiation and the molecular gas. It is necessary to increase the sample of molecular clouds located at different distances and affected in different ways by nearby or embedded H ii regions and OB associations to study the selective photodissociation. Using 12CO, 13CO, and C18O J = 1–0 data obtained from the FOREST unbiased Galactic plane imaging survey performed with the Nobeyama 45-m telescope, we analyse the filamentary infrared dark cloud IRDC $34.43+0.24$ located at the distance of about 3.9 kpc. This infrared dark cloud (IRDC) is related to several H ii regions and young stellar objects. Assuming local thermodynamic equilibrium, we obtain: $0.8 \times 10^{16} <$ N(13CO) $<4 \times 10^{17}$ cm–2 (average value $= 4.2 \times 10^{16}$ cm–2), $0.6 \times 10^{15} <$ N(C18O) $<4.4 \times 10^{16}$ cm–2 (average value $= 5.0 \times 10^{15}$ cm–2), and 3 $<$ $X^{13/18}$ $<$ 30 (average $= 8$ ) across the whole IRDC. Larger values of $X^{13/18}$ were found towards portions of the cloud related to the H ii regions associated with the N61 and N62 bubbles and with the photodissociation regions, precisely the regions in which FUV photons are strongly interacting with the molecular gas. Our result represents an observational support to the C18O selectively photodissociation phenomenon occurring in a quite distant filamentary IRDC. Additionally, based on IR data from the Hi-GAL survey, the FUV radiation field was estimated in Habing units, and the dust temperature (T $_{dust}$ ) and H2 column density (N(H2)) distribution were studied. Using the average of N(H2), values in close agreement with the ‘canonical’ abundance ratios [H2]/[13CO] and [H2]/[C18O] were derived. However, the obtained ranges in the abundance ratios show that if an accurate analysis of the molecular gas is required, the use of the ‘canonical’ values may introduce some bias. Thus, it is important to consider how the gas is irradiated by the FUV photons across the molecular cloud. The analysis of $X^{13/18}$ is a good tool to perform that. Effects of beam dilution and clumpiness were studied.

scholarly journals Measurements of Isotopic Abundances in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 397-404 ◽  
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.

scholarly journals Carbon Recombination Lines at 34.5 MHz from the Galactic Plane

2002 ◽  
Vol 199 ◽  
pp. 347-348
Author(s):  
N.G. Kantharia ◽  
K.R. Anantharamaiah
Keyword(s):  
Galactic Plane ◽  
Galactic Disk ◽  
Radio Recombination Lines ◽  
Physical Conditions

We report the detection of carbon radio recombination lines (CRRLs) near 34.5 MHz (n ∼ 575) and near 328 MHz (n ∼ 270) from 6 positions with l < 17°, b = 0°. Modelling the data shows that the observed CRRLs can arise under a range of physical conditions which are found in atomic HI, molecular and photo-dissociation regions (PDRs) in the galactic disk.

scholarly journals The Evolution of Giant Molecular Clouds

1980 ◽  
Vol 87 ◽  
pp. 137-149 ◽  
Author(s):  
Colin Norman ◽  
Joseph Silk
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Density Wave ◽  
Collective Effects ◽  
Giant Molecular Clouds ◽  
Spiral Density Wave ◽  
External Galaxies ◽  
Co Observations

We discuss the origin, lifetime, destruction, spatial distribution and relation to star formation of giant molecular clouds. A coagulation model including the effects of spiral density wave shocks is described. We explore implications for CO observations of external galaxies. The collective effects of OB star winds and supernova remnants in disrupting clouds are considered.

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