scholarly journals Molecular Cloud Formation in Shock‐compressed Layers

2000 ◽  
Vol 532 (2) ◽  
pp. 980-993 ◽  
Author(s):  
Hiroshi Koyama ◽  
Shu‐Ichiro Inutsuka
Keyword(s):  
Molecular Cloud ◽  
Cloud Formation

scholarly journals Histogram of oriented gradients: a technique for the study of molecular cloud formation

2019 ◽  
Vol 622 ◽  
pp. A166 ◽  
Author(s):  
J. D. Soler ◽  
H. Beuther ◽  
M. Rugel ◽  
Y. Wang ◽  
P. C. Clark ◽  
...  
Keyword(s):  
Spectral Line ◽  
Spatial Correlation ◽  
Molecular Cloud ◽  
Galactic Plane ◽  
Cloud Formation ◽  
Molecular Gas ◽  
Histogram Of Oriented Gradients ◽  
Spatial Correlations ◽  
Mhd Turbulence ◽  
Physical Conditions

We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of spectral line observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterized HOG using synthetic observations of HI and 13CO (J = 1 → 0) emission from numerical simulations of magnetohydrodynamic (MHD) turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We found a significant spatial correlation between the two tracers in velocity channels where vHI ≈ v13CO, almost independent of the orientation of the collision with respect to the line of sight. Subsequently, we used HOG to investigate the spatial correlation of the HI, from The HI/OH/recombination line survey of the inner Milky Way (THOR), and the 13CO (J = 1 → 0) emission from the Galactic Ring Survey (GRS), toward the portion of the Galactic plane 33°.75 ≤l ≤ 35°.25 and |b| ≤ 1°.25. We found a significant spatial correlation between the two tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption (HISA) features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results derived for the observational data indicate significant differences between individual regions: some show spatial correlation in channels around vHI ≈ v13CO while others present spatial correlations in velocity channels separated by a few kilometers per second. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.

scholarly journals Deterministic Self-Propagating Star Formation

1989 ◽  
Vol 120 ◽  
pp. 518-523
Author(s):  
Jan Palouš
Keyword(s):  
Star Formation ◽  
Simple Model ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Evolution ◽  
Cloud Formation ◽  
Rotating Disks ◽  
Atomic Gas ◽  
High Column

AbstractThe evolution of large scale expanding structures in differentially rotating disks is studied. High column densities in some places may eventually lead to molecular cloud formation and initiate also star-formation. After some time, multi-structured arms evolve, where regions of intensive star-formation are separated from each other by regions of atomic gas or molecular clouds. This is due to the deterministic nature and to the coherence of this process. A simple model of galactic evolution is introduced and the different behaviour of Sa, Sb, and Sc galaxies is shown.

scholarly journals Molecular cloud formation by compression of magnetized turbulent gas subjected to radiative cooling

2020 ◽  
Vol 493 (3) ◽  
pp. 3098-3113 ◽  
Author(s):  
Ankush Mandal ◽  
Christoph Federrath ◽  
Bastian Körtgen
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Turnover Rate ◽  
Radiative Heating ◽  
Cloud Formation ◽  
Neutral Medium ◽  
Contraction Rate ◽  
Mhd Turbulence ◽  
Cloud Properties ◽  
Hydrodynamical Simulations

ABSTRACT Complex turbulent motions of magnetized gas are ubiquitous in the interstellar medium (ISM). The source of this turbulence, however, is still poorly understood. Previous work suggests that compression caused by supernova shockwaves, gravity, or cloud collisions, may drive the turbulence to some extent. In this work, we present three-dimensional (3D) magnetohydrodynamic (MHD) simulations of contraction in turbulent, magnetized clouds from the warm neutral medium of the ISM to the formation of cold dense molecular clouds, including radiative heating and cooling. We study different contraction rates and find that observed molecular cloud properties, such as the temperature, density, Mach number, and magnetic field strength, and their respective scaling relations, are best reproduced when the contraction rate equals the turbulent turnover rate. In contrast, if the contraction rate is significantly larger (smaller) than the turnover rate, the compression drives too much (too little) turbulence, producing unrealistic cloud properties. We find that the density probability distribution function evolves from a double lognormal representing the two-phase ISM, to a skewed, single lognormal in the dense, cold phase. For purely hydrodynamical simulations, we find that the effective driving parameter of contracting cloud turbulence is natural to mildly compressive (b ∼ 0.4–0.5), while for MHD turbulence, we find b ∼ 0.3–0.4, i.e. solenoidal to naturally mixed. Overall, the physical properties of the simulated clouds that contract at a rate equal to the turbulent turnover rate, indicate that large-scale contraction may explain the origin and evolution of turbulence in the ISM.

scholarly journals The Supershell-Molecular Cloud Connection in the Milky Way and Beyond

2012 ◽  
Vol 8 (S292) ◽  
pp. 83-86
Author(s):  
J. R. Dawson ◽  
N. M. McClure-Griffiths ◽  
Y. Fukui ◽  
J. Dickey ◽  
T. Wong ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Observational Evidence ◽  
Cloud Formation ◽  
Stellar Feedback ◽  
The Relationship ◽  
Global Contribution

AbstractThe role of large-scale stellar feedback in the formation of molecular clouds has been investigated observationally by examining the relationship between Hi and 12CO(J = 1−0) in supershells. Detailed parsec-resolution case studies of two Milky Way supershells demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. Recent results on supergiant shells in the LMC suggest that while they do indeed help to organise the ISM into over-dense structures, their global contribution to molecular cloud formation is of the order of only ∼ 10%.

scholarly journals The driving of turbulence in simulations of molecular cloud formation and evolution

2017 ◽  
Vol 472 (2) ◽  
pp. 2496-2503 ◽  
Author(s):  
Bastian Körtgen ◽  
Christoph Federrath ◽  
Robi Banerjee
Keyword(s):  
Molecular Cloud ◽  
Cloud Formation ◽  
Formation And Evolution

scholarly journals Erratum: Molecular cloud formation as seen in synthetic H i and molecular gas observations

2016 ◽  
Vol 456 (3) ◽  
pp. 3212-3212
Author(s):  
Jonathan S. Heiner ◽  
Enrique Vázquez-Semadeni ◽  
Javier Ballesteros-Paredes
Keyword(s):  
Molecular Cloud ◽  
Cloud Formation ◽  
Molecular Gas

scholarly journals THE EFFECTS OF FLOW-INHOMOGENEITIES ON MOLECULAR CLOUD FORMATION: LOCAL VERSUS GLOBAL COLLAPSE

2014 ◽  
Vol 790 (1) ◽  
pp. 37 ◽  
Author(s):  
Jonathan J. Carroll-Nellenback ◽  
Adam Frank ◽  
Fabian Heitsch
Keyword(s):  
Molecular Cloud ◽  
Cloud Formation ◽  
Global Collapse
Sign in / Sign up

Export Citation Format

Share Document