Dust extinction and molecular gas in the dark cloud IC 5146

1994 ◽  
Vol 429 ◽  
pp. 694 ◽  
Author(s):  
Charles J. Lada ◽  
Elizabeth A. Lada ◽  
Dan P. Clemens ◽  
John Bally
Keyword(s):  
Molecular Gas ◽  
Dark Cloud ◽  
Dust Extinction

Morphology and Energetics of the Molecular Gas within a Core and a Diffuse Region in the Filamentary Dark Cloud GF 9

2000 ◽  
Vol 120 (1) ◽  
pp. 393-406 ◽  
Author(s):  
David R. Ciardi ◽  
Charles E. Woodward ◽  
Dan P. Clemens ◽  
David E. Harker ◽  
Richard J. Rudy
Keyword(s):  
Molecular Gas ◽  
Dark Cloud ◽  
Diffuse Region

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.

Structure and kinematics of molecular jets

1986 ◽  
Vol 64 (4) ◽  
pp. 431-433 ◽  
Author(s):  
Ronald L. Snell
Keyword(s):  
Stellar Wind ◽  
High Velocity ◽  
Observational Studies ◽  
Molecular Gas ◽  
Dark Cloud ◽  
Star Forming ◽  
Molecular Outflows ◽  
Star Forming Regions ◽  
Cloud Material

Observational studies of the structure and kinematics of the supersonic molecular gas in star-forming regions are reviewed. These studies have suggested that the bulk of the high-velocity gas may be ambient-cloud material swept up by a collimated stellar wind. The actual structures of these outflows, however, are poorly understood. One source that may provide a better understanding of molecular outflows is that in the nearby dark cloud L1551. New observations of this outflow are presented and discussed in context of the models proposed by Snell and Schloerb.

scholarly journals Molecule Formation in External Galaxies

1992 ◽  
Vol 150 ◽  
pp. 121-126
Author(s):  
T J Millar ◽  
E. Herbst
Keyword(s):  
Starburst Galaxies ◽  
Molecular Gas ◽  
Dark Cloud ◽  
Elemental Abundances ◽  
Molecule Formation ◽  
Cloud Models ◽  
External Galaxies ◽  
Molecular Abundances

We discuss the parameters needed to model chemistry in extragalactic clouds. While density and temperature can be constrained by multiline observations, molecular abundances may be severely affected by the adopted elemental abundances. While the observations of the Magelllanic Clouds can be reasonably interpreted in terms of dark cloud models, molecular gas in starburst galaxies could well be dominated by photoeffects. The detection of deuterium in extragalactic molecules would provide a valuable diagnostic.

scholarly journals Dynamical cloud formation traced by atomic and molecular gas

2020 ◽  
Vol 638 ◽  
pp. A44 ◽  
Author(s):  
H. Beuther ◽  
Y. Wang ◽  
J. Soler ◽  
H. Linz ◽  
J. Henshaw ◽  
...  
Keyword(s):  
Spectral Line ◽  
Mass Flow ◽  
Velocity Structure ◽  
Function Analysis ◽  
Cloud Formation ◽  
Molecular Gas ◽  
Gas Flows ◽  
Dark Cloud ◽  
Flow Rates ◽  
Mass Flow Rates

Context. Atomic and molecular cloud formation is a dynamical process. However, kinematic signatures of these processes are still observationally poorly constrained. Aims. We identify and characterize the cloud formation signatures in atomic and molecular gas. Methods. Targeting the cloud-scale environment of the prototypical infrared dark cloud G28.3, we employed spectral line imaging observations of the two atomic lines HI and [CI] as well as molecular lines observations in 13CO in the 1–0 and 3–2 transitions. The analysis comprises investigations of the kinematic properties of the different tracers, estimates of the mass flow rates, velocity structure functions, a histogram of oriented gradients (HOG) study, and comparisons to simulations. Results. The central infrared dark cloud (IRDC) is embedded in a more diffuse envelope of cold neutral medium traced by HI self-absorption and molecular gas. The spectral line data as well as the HOG and structure function analysis indicate a possible kinematic decoupling of the HI from the other gas compounds. Spectral analysis and position–velocity diagrams reveal two velocity components that converge at the position of the IRDC. Estimated mass flow rates appear rather constant from the cloud edge toward the center. The velocity structure function analysis is consistent with gas flows being dominated by the formation of hierarchical structures. Conclusions. The observations and analysis are consistent with a picture where the IRDC G28.3 is formed at the center of two converging gas flows. While the approximately constant mass flow rates are consistent with a self-similar, gravitationally driven collapse of the cloud, external compression (e.g., via spiral arm shocks or supernova explosions) cannot be excluded yet. Future investigations should aim at differentiating the origin of such converging gas flows.

scholarly journals MILLIMETER AND FAR-IR STUDY OF THE IRDC SDC 341.232-0.268

2019 ◽  
Vol 55 (2) ◽  
pp. 289-303
Author(s):  
M. M. Vazzano ◽  
C. E. Cappa ◽  
V. Firpo ◽  
C. H. López-Caraballo ◽  
M. Rubio ◽  
...  
Keyword(s):  
Molecular Data ◽  
High Density ◽  
Molecular Gas ◽  
Evolutionary Status ◽  
Dark Cloud ◽  
Molecular Lines ◽  
Ir Study ◽  
Cold Dust

We analyze the molecular gas and dust associated with the infrared dark cloud SDC 341.232-0.268 in order to investigate the characteristics and parameters of the gas, determine the evolutionary status of four embedded EGO candidates, and establish possible infall or outflow gas motions. We base our study on 12 CO(2-1), 13 CO(2-1), and C18 O(2-1) data obtained with the APEX telescope, molecular data of high density tracers from the MALT90 survey and IR images from Spitzer, Herschel and ATLASGAL. The study reveals two clumps at −44 km/s towards the IRDC, with densities of > 104 cm^{−3}, typical of IRDCs, while high density tracers show H2 densities > 105 . FIR images reveals the presence of cold dust linked to the molecular clumps and EGOs. A comparison of the spectra of the optically thin and optically thick molecular lines towards the EGOs suggests the existence of infall and outflow motions.

scholarly journals Modeling sulfur depletion in interstellar clouds

2019 ◽  
Vol 624 ◽  
pp. A108 ◽  
Author(s):  
Jacob C. Laas ◽  
Paola Caselli
Keyword(s):  
Gas Phase ◽  
Chemical Elements ◽  
Reaction Network ◽  
Interstellar Cloud ◽  
Molecular Gas ◽  
Dark Cloud ◽  
Interstellar Clouds ◽  
Simple Physical Model ◽  
Molecular Abundances ◽  
Elemental Depletion

Context. The elemental depletion of interstellar sulfur from the gas phase has been a recurring challenge for astrochemical models. Observations show that sulfur remains relatively non-depleted with respect to its cosmic value throughout the diffuse and translucent stages of an interstellar molecular cloud, but its atomic and molecular gas-phase constituents cannot account for this cosmic value toward lines of sight containing higher-density environments. Aims. We have attempted to address this issue by modeling the evolution of an interstellar cloud from its pristine state as a diffuse atomic cloud to a molecular environment of much higher density, using a gas-grain astrochemical code and an enhanced sulfur reaction network. Methods. A common gas-grain astrochemical reaction network has been systematically updated and greatly extended based on previous literature and previous sulfur models, with a focus on the grain chemistry and processes. A simple astrochemical model was used to benchmark the resulting network updates, and the results of the model were compared to typical astronomical observations sourced from the literature. Results. Our new gas-grain astrochemical model is able to reproduce the elemental depletion of sulfur, whereby sulfur can be depleted from the gas-phase by two orders of magnitude, and that this process may occur under dark cloud conditions if the cloud has a chemical age of at least 106 years. The resulting mix of sulfur-bearing species on the grain ranges across all the most common chemical elements (H/C/N/O), not dissimilar to the molecules observed in cometary environments. Notably, this mixture is not dominated simply by H2S, unlike all other current astrochemical models. Conclusions. Despite our relatively simple physical model, most of the known gas-phase S-bearing molecular abundances are accurately reproduced under dense conditions, however they are not expected to be the primary molecular sinks of sulfur. Our model predicts that most of the “missing” sulfur is in the form of organo-sulfur species that are trapped on grains.

Central kiloparsec of NGC 1326 observed with SINFONI

2020 ◽  
Vol 638 ◽  
pp. A53
Author(s):  
Nastaran Fazeli ◽  
Gerold Busch ◽  
Andreas Eckart ◽  
Françoise Combes ◽  
Persis Misquitta ◽  
...  
Keyword(s):  
Black Hole ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Velocity Fields ◽  
Molecular Gas ◽  
Nearby Galaxy ◽  
Stellar Content ◽  
Stellar Rotation ◽  
Supermassive Black Hole ◽  
Integral Field Spectrograph

Gas inflow processes in the vicinity of galactic nuclei play a crucial role in galaxy evolution and supermassive black hole growth. Exploring the central kiloparsec of galaxies is essential to shed more light on this subject. We present near-infrared H- and K-band results of the nuclear region of the nearby galaxy NGC 1326, observed with the integral-field spectrograph SINFONI mounted on the Very Large Telescope. The field of view covers 9″ × 9″ (650 × 650 pc2). Our work is concentrated on excitation conditions, morphology, and stellar content. The nucleus of NGC 1326 was classified as a LINER, however in our data we observed an absence of ionised gas emission in the central r ∼ 3″. We studied the morphology by analysing the distribution of ionised and molecular gas, and thereby detected an elliptically shaped, circum-nuclear star-forming ring at a mean radius of 300 pc. We estimate the starburst regions in the ring to be young with dominating ages of < 10 Myr. The molecular gas distribution also reveals an elongated east to west central structure about 3″ in radius, where gas is excited by slow or mild shock mechanisms. We calculate the ionised gas mass of 8 × 105 M⊙ completely concentrated in the nuclear ring and the warm molecular gas mass of 187 M⊙, from which half is concentrated in the ring and the other half in the elongated central structure. The stellar velocity fields show pure rotation in the plane of the galaxy. The gas velocity fields show similar rotation in the ring, but in the central elongated H2 structure they show much higher amplitudes and indications of further deviation from the stellar rotation in the central 1″ aperture. We suggest that the central 6″ elongated H2 structure might be a fast-rotating central disc. The CO(3–2) emission observations with the Atacama Large Millimeter/submillimeter Array reveal a central 1″ torus. In the central 1″ of the H2 velocity field and residual maps, we find indications for a further decoupled structure closer to a nuclear disc, which could be identified with the torus surrounding the supermassive black hole.

Kinetics of a nonequilibrium molecular gas

1988 ◽  
Vol 155 (7) ◽  
pp. 545-545
Author(s):  
Boris M. Smirnov
Keyword(s):  
Molecular Gas ◽  
Kinetics Of
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