scholarly journals The geometry and dynamical role of stellar wind bubbles in photoionized H ii regions

2020 ◽  
Vol 501 (1) ◽  
pp. 1352-1369
Author(s):  
Sam Geen ◽  
Rebekka Bieri ◽  
Joakim Rosdahl ◽  
Alex de Koter
Keyword(s):  
Molecular Clouds ◽  
Gas Flows ◽  
H Ii Regions ◽  
Star Forming ◽  
3D Geometry ◽  
Thermally Driven ◽  
Magnetohydrodynamic Simulations ◽  
Analytic Models ◽  
Stellar Source

ABSTRACT Winds from young massive stars contribute a large amount of energy to their host molecular clouds. This has consequences for the dynamics and observable structure of star-forming clouds. In this paper, we present radiative magnetohydrodynamic simulations of turbulent molecular clouds that form individual stars of 30, 60, and 120 solar masses emitting winds and ultraviolet radiation following realistic stellar evolution tracks. We find that winds contribute to the total radial momentum carried by the expanding nebula around the star at 10 per cent of the level of photoionization feedback, and have only a small effect on the radial expansion of the nebula. Radiation pressure is largely negligible in the systems studied here. The 3D geometry and evolution of wind bubbles is highly aspherical and chaotic, characterized by fast-moving ‘chimneys’ and thermally driven ‘plumes’. These plumes can sometimes become disconnected from the stellar source due to dense gas flows in the cloud. Our results compare favourably with the findings of relevant simulations, analytic models and observations in the literature while demonstrating the need for full 3D simulations including stellar winds. However, more targeted simulations are needed to better understand results from observational studies.

scholarly journals Structure and expansion law of H ii regions in structured molecular clouds

2019 ◽  
Vol 487 (2) ◽  
pp. 2200-2214 ◽  
Author(s):  
Manuel Zamora-Avilés ◽  
Enrique Vázquez-Semadeni ◽  
Ricardo F González ◽  
José Franco ◽  
Steven N Shore ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Massive Star ◽  
Mean Value ◽  
Neutral Medium ◽  
H Ii Regions ◽  
Star Forming ◽  
Star Forming Regions ◽  
H Ii Region ◽  
Analytical Result ◽  
Magnetohydrodynamic Simulations

Abstract We present radiation-magnetohydrodynamic simulations aimed at studying evolutionary properties of H ii regions in turbulent, magnetized, and collapsing molecular clouds formed by converging flows in the warm neutral medium. We focus on the structure, dynamics, and expansion laws of these regions. Once a massive star forms in our highly structured clouds, its ionizing radiation eventually stops the accretion (through filaments) towards the massive star-forming regions. The new overpressured H ii regions push away the dense gas, thus disrupting the more massive collapse centres. Also, because of the complex density structure in the cloud, the H ii regions expand in a hybrid manner: they virtually do not expand towards the densest regions (cores), while they expand according to the classical analytical result towards the rest of the cloud, and in an accelerated way, as a blister region, towards the diffuse medium. Thus, the ionized regions grow anisotropically, and the ionizing stars generally appear off-centre of the regions. Finally, we find that the hypotheses assumed in standard H ii-region expansion models (fully embedded region, blister-type, or expansion in a density gradient) apply simultaneously in different parts of our simulated H ii regions, producing a net expansion law (R∝ tα, with α in the range of 0.93–1.47 and a mean value of 1.2 ± 0.17) that differs from any of those of the standard models.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

1987 ◽  
Vol 115 ◽  
pp. 499-499 ◽  
Author(s):  
P. M. Solomon
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Formation Mechanisms ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Two Populations ◽  
Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals Characteristics of H2CO Towards Star-Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 171-171
Author(s):  
H. R. Dickel ◽  
W. M. Goss ◽  
A. H. Rots
Keyword(s):  
Molecular Clouds ◽  
H Ii Regions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Compact Region ◽  
Dense Cores ◽  
H Ii Region ◽  
Narrow Width ◽  
Water Masers ◽  
Small Clusters

Small clusters of recently-formed massive stars with their associated compact H II regions are often found embedded in the dense cores of molecular clouds. The H2CO opacity is correlated with the compactness of the H II region and is especially high for those with associated maser activity although additional factors are involved for the ultra-compact H II regions (UCH II). VLA observations of H2CO at 2 cm have been made towards the UCH II regions of W49-north. The highest H2CO opacity of 1.0 is found towards region A which does not have maser activity; yet one of the most compact region C, has an H2CO opacity of only 0.3, For these sources the integrated H2CO opacity (over the entire profile) may be more indicative of compactness. This may be due to the broader H2CO lines which can occur towards the maser regions. For example, large line widths of 10 to 12 km s−1 ate found towards W49-north G where the most intense water masers are located and towards W49-north B which has OH masers. The H2CO line with the highest 2 cm opacity of 2.5 and a narrow width of 2 km s−1 is found towards the UCH II region ON 3 which has only weak H2O maser emission.

scholarly journals Star-forming Substructure within Molecular Clouds

2012 ◽  
Vol 8 (S292) ◽  
pp. 29-34
Author(s):  
James Di Francesco
Keyword(s):  
Molecular Clouds ◽  
Far Infrared ◽  
High Mass ◽  
Wide Field ◽  
Relative Role ◽  
Space Observatory ◽  
Star Forming ◽  
Filament Networks ◽  
Different Parts

AbstractWide-field far-infrared/submillimeter continuum maps of molecular clouds by the Herschel Space Observatory GBS and HOBYS surveys are revealing the star-forming substructures that lead to star formation in dense gas. In particular, these maps have revealed the central role in clouds of filaments, likely formed through turbulent motions. These filaments appear to be non-isothermal and fragment into cores only when their column densities exceed a stability threshold. Organizations of filament networks suggest the relative role of turbulence and gravity can be traced in different parts of a cloud, and filament intersections may lead to larger amounts of mass flow that form the precursors of high-mass stars or clusters.

scholarly journals The role of galactic dynamics in shaping the physical properties of giant molecular clouds in Milky Way-like galaxies

2020 ◽  
Vol 498 (1) ◽  
pp. 385-429 ◽  
Author(s):  
Sarah M R Jeffreson ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller ◽  
Mélanie Chevance ◽  
Simon C O Glover
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Gravitational Instability ◽  
Formation Rate ◽  
Tangential Velocity ◽  
Galactic Rotation ◽  
H Ii Regions ◽  
Giant Molecular Clouds

ABSTRACT We examine the role of the large-scale galactic-dynamical environment in setting the properties of giant molecular clouds in Milky Way-like galaxies. We perform three high-resolution simulations of Milky Way-like discs with the moving-mesh hydrodynamics code arepo, yielding a statistical sample of ${\sim}80\, 000$ giant molecular clouds and ${\sim}55\, 000$ H i clouds. We account for the self-gravity of the gas, momentum, and thermal energy injection from supernovae and H ii regions, mass injection from stellar winds, and the non-equilibrium chemistry of hydrogen, carbon, and oxygen. By varying the external gravitational potential, we probe galactic-dynamical environments spanning an order of magnitude in the orbital angular velocity, gravitational stability, mid-plane pressure, and the gradient of the galactic rotation curve. The simulated molecular clouds are highly overdense (∼100×) and overpressured (∼25×) relative to the ambient interstellar medium. Their gravoturbulent and star-forming properties are decoupled from the dynamics of the galactic mid-plane, so that the kpc-scale star formation rate surface density is related only to the number of molecular clouds per unit area of the galactic mid-plane. Despite this, the clouds display clear, statistically significant correlations of their rotational properties with the rates of galactic shearing and gravitational free-fall. We find that galactic rotation and gravitational instability can influence their elongation, angular momenta, and tangential velocity dispersions. The lower pressures and densities of the H i clouds allow for a greater range of significant dynamical correlations, mirroring the rotational properties of the molecular clouds, while also displaying a coupling of their gravitational and turbulent properties to the galactic-dynamical environment.

scholarly journals Molecular line ratio diagnostics along the radial cut and dusty ultraviolet-bright clumps in a spiral galaxy NGC 0628

2020 ◽  
Vol 495 (3) ◽  
pp. 2682-2712
Author(s):  
Selçuk Topal
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Line Ratio ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
Molecular Lines ◽  
Co Gas

ABSTRACT Molecular emission lines are essential tools to shed light on many questions regarding star formation in galaxies. Multiple molecular lines are particularly useful to probe different phases of star-forming molecular clouds. In this study, we investigate the physical properties of giant molecular clouds (GMCs) using multiple lines of CO, i.e. CO(1–0, 2–1, 3–2) and 13CO(1–0), obtained at selected 20 positions in the disc of NGC 0628. A total of 11 positions were selected over the radial cut, including the centre, and remaining 9 positions were selected across the southern and northern arms of the galaxy. A total of 13 out of 20 positions are brighter at $24\, \mu {\rm m}$ and ultraviolet (UV) emission and hosting significantly more H ii regions compared to the rest of the positions indicating opposite characteristics. Our line ratio analysis shows that the gas gets warmer and thinner as a function of radius from the galaxy centre up to 1.7 kpc, and then the ratios start to fluctuate. Our empirical and model results suggest that the UV-bright positions have colder and thinner CO gas with higher hydrogen and CO column densities. However, the UV-dim positions have relatively warmer CO gas with lower densities bathed in GMCs surrounded by less number of H ii regions. Analysis of multiwavelength infrared and UV data indicates that the UV-bright positions have higher star formation efficiency than that of the UV-dim positions.

Observations of magnetic fields in star-forming clouds

2018 ◽  
Vol 14 (A30) ◽  
pp. 101-101
Author(s):  
Juan D. Soler
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Spatial Scales ◽  
Cloud Formation ◽  
Star Forming ◽  
Formation And Evolution ◽  
Under Construction ◽  
The Magnetic Field

AbstractThis review examines observations of magnetic fields in molecular clouds, that is, at spatial scales ranging from tens to tenths of parsecs and densities up to hundreds of particles per cubic centimetre. I will briefly summarize the techniques for observing and mapping magnetic fields in molecular clouds. I will review important examples of observational results obtained using each technique and their implications for our understanding of the role of the magnetic field in molecular cloud formation and evolution. Finally, I will briefly discuss the prospects for advances in our observational capabilities with telescopes and instruments now beginning operation or under construction.

scholarly journals ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

2020 ◽  
Author(s):  
Hidetoshi Sano ◽  
Kisetsu Tsuge ◽  
Kazuki Tokuda ◽  
Kazuyuki Muraoka ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Line Emission ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Giant Molecular Cloud

Abstract We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.

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