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

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.

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Triggered high-mass star formation in the H ii region W 28 A2: A cloud–cloud collision scenario

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa054 ◽

2020 ◽

Author(s):

Katsuhiro Hayashi ◽

Satoshi Yoshiike ◽

Rei Enokiya ◽

Shinji Fujita ◽

Rin Yamada ◽

...

Keyword(s):

Star Formation ◽

Intensity Ratio ◽

Molecular Clouds ◽

Early Stage ◽

Infrared Emission ◽

Radio Continuum ◽

High Mass ◽

Continuum Emission ◽

Mass Star ◽

H Ii Region

Abstract We report on a study of the high-mass star formation in the H ii region W 28 A2 by investigating the molecular clouds that extend over ∼5–10 pc from the exciting stars using the 12CO and 13CO (J = 1–0) and 12CO (J = 2–1) data taken by NANTEN2 and Mopra observations. These molecular clouds consist of three velocity components with CO intensity peaks at VLSR ∼ −4 km s−1, 9 km s−1, and 16 km s−1. The highest CO intensity is detected at VLSR ∼ 9 km s−1, where the high-mass stars with spectral types O6.5–B0.5 are embedded. We found bridging features connecting these clouds toward the directions of the exciting sources. Comparisons of the gas distributions with the radio continuum emission and 8 μm infrared emission show spatial coincidence/anti-coincidence, suggesting physical associations between the gas and the exciting sources. The 12CO J = 2–1 to 1–0 intensity ratio shows a high value (≳0.8) toward the exciting sources for the −4 km s−1 and +9 km s−1 clouds, possibly due to heating by the high-mass stars, whereas the intensity ratio at the CO intensity peak (VLSR ∼ 9 km s−1) decreases to ∼0.6, suggesting self absorption by the dense gas in the near side of the +9 km s−1 cloud. We found partly complementary gas distributions between the −4 km s−1 and +9 km s−1 clouds, and the −4 km s−1 and +16 km s−1 clouds. The exciting sources are located toward the overlapping region in the −4 km s−1 and +9 km s−1 clouds. Similar gas properties are found in the Galactic massive star clusters RCW 38 and NGC 6334, where an early stage of cloud collision to trigger the star formation is suggested. Based on these results, we discuss the possibility of the formation of high-mass stars in the W 28 A2 region being triggered by cloud–cloud collision.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900096297 ◽

1987 ◽

Vol 115 ◽

pp. 499-499 ◽

Cited By ~ 2

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.

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Supernova feedback and the energy deposition in molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa451 ◽

2020 ◽

Vol 493 (4) ◽

pp. 4700-4710 ◽

Cited By ~ 4

Author(s):

William E Lucas ◽

Ian A Bonnell ◽

James E Dale

Keyword(s):

Galaxy Formation ◽

Supernova Explosion ◽

High Mass ◽

Stellar Winds ◽

Mass Star ◽

Stellar Feedback ◽

The Galaxy ◽

Weak Points ◽

Supernova Explosions ◽

Supernova Feedback

Abstract Feedback from supernovae is often invoked as an important process in limiting star formation, removing gas from galaxies and, hence, as a determining process in galaxy formation. Here, we report on numerical simulations, investigating the interaction between supernova explosions and the natal molecular cloud. We also consider the cases with and without previous feedback from the high-mass star in the form of ionizing radiation and stellar winds. The supernova is able to find weak points in the cloud and creates channels through which it can escape, leaving much of the well-shielded cloud largely unaffected. This effect is increased when the channels are preexisting due to the effects of previous stellar feedback. The expanding supernova deposits its energy in the gas that is in these exposed channels, and, hence, sweeps up less mass when feedback has already occurred, resulting in faster outflows with less radiative losses. The full impact of the supernova explosion is then able to impact the larger scale of the galaxy in which it abides. We conclude that supernova explosions have only moderate effects on their dense natal environments but that with preexisting feedback, the energetic effects of the supernova are able to escape and affect the wider scale medium of the galaxy.

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Characterising the high-mass star forming filament G351.776–0.527 with Herschel and APEX dust continuum and gas observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833612 ◽

2019 ◽

Vol 621 ◽

pp. A130 ◽

Cited By ~ 4

Author(s):

S. Leurini ◽

E. Schisano ◽

T. Pillai ◽

A. Giannetti ◽

J. Urquhart ◽

...

Keyword(s):

Large Scale ◽

Galactic Plane ◽

Constant Width ◽

Stable State ◽

Far Infrared ◽

High Mass ◽

Mass Star ◽

Large Reservoir ◽

Main Structure ◽

Main Filament

G351.776-0.527 is among the most massive, closest, and youngest filaments in the inner Galactic plane and therefore it is an ideal laboratory to study the kinematics of dense gas and mass replenishment on a large scale. In this paper, we present far-infrared and submillimetre wavelength continuum observations combined with spectroscopic C18O (2–1) data of the entire region to study its temperature, mass distribution, and kinematics. The structure is composed of a main elongated region with an aspect ratio of ~23, which is associated with a network of filamentary structures. The main filament has a remarkably constant width of 0.2 pc. The total mass of the network (including the main filament) is ≥2600M⊙, while we estimate a mass of ~2000M⊙ for the main structure. Therefore, the network harbours a large reservoir of gas and dust that could still be accreted onto the main structure. From the analysis of the gas kinematics, we detect two velocity components in the northern part of the main filament. The data also reveal velocity oscillations in C18O along the spine in the main filament and in at least one of the branches. Considering the region as a single structure, we find that it is globally close to virial equilibrium indicating that the entire structure is approximately in a stable state.

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Star-forming Substructure within Molecular Clouds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000185 ◽

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.

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Large scale Structure of HI in other Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900089099 ◽

1991 ◽

Vol 144 ◽

pp. 201-212

Author(s):

Thijs Van Der Hulst ◽

Jurjen Kamphuis

Keyword(s):

Atomic Hydrogen ◽

Large Scale ◽

Stellar Winds ◽

Large Scale Structures ◽

Neutral Gas ◽

Peculiar Velocities ◽

Show Evidence ◽

Supernova Explosions ◽

Nearby Galaxies ◽

Scale Structures

In this paper we discuss the large-scale structures (> 500 pc) of the neutral atomic hydrogen in the disk of nearby galaxies, with an emphasis on finding evidence for neutral gas features in the disk - halo interface. Most nearby galaxies studied in detail appear to have hole and shell type structures in their HI disks and several show evidence for gas at peculiar velocities, probably examples of gas streaming out of the disk into the halo. Not all of the observed phenomena can be explained by stellar winds and supernova explosions and other explanations will briefly be discussed.

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