Evidence for the Existence of a Low-Velocity Molecular Cloud near Sgr A

1978 ◽  
Vol 3 (4) ◽  
pp. 266-269 ◽  
Author(s):  
J. B. Whiteoak ◽  
F. F. Gardner
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Galactic Centre ◽  
The Sun ◽  
Low Velocity ◽  
High Velocity Resolution ◽  
Sgr A ◽  
Galactic Longitude ◽  
Co Observations

In the wide complex profiles of OH, H2CO and CO spectra observed in directions towards the galactic centre, only the features at radial velocities near + 40 km s-1 are generally believed to originate in the molecular clouds nearest the galactic nucleus. The features at other velocities are associated with clouds or spiral features that can be traced over larger ranges of galactic longitude, implying locations which are more distant from the nucleus. In particular, the features near zero velocity have been traditionally associated with molecular clouds within 1-2 kpc of the Sun. However, H2CO observations with high velocity resolution provide evidence that one cloud with velocity near zero is probably near the galactic nucleus.

scholarly journals C18O and HNCO in the Galactic Centre

1996 ◽  
Vol 169 ◽  
pp. 281-282
Author(s):  
M. Lindqvist ◽  
Aa. Sandqvist ◽  
A. Winnberg ◽  
L.-Å. Nyman ◽  
F. Combes ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Radio Continuum ◽  
Galactic Centre ◽  
Galactic Latitude ◽  
Sgr A ◽  
Galactic Longitude

Using the SEST, we have observed 554 positions with a spacing of 45″ in the C18O(J = 1 → 0) and HNCO(Jkk′ = 505 → 404) lines. The data covers most of the Sgr A region including the Arc. Many of the dominant clouds in the GC region (see e.g. Güsten et al. 1981, A&A 103, 197; Bally et al. 1987, ApJS, 65, 13) are readily identified in the total integrated C18O and HNCO maps (Fig. 1). The results will be published in A&AS and will include intensity maps with 5 km s–1 velocity resolutions, as well as galactic longitude-velocity and galactic latitude-velocity maps. J = 2 → 1 C18O observations are planned for selected regions. The objectives of the project are twofold: 1. Geometrical, morphological, and dynamical relationships between the molecular regions and the radio continuum sources. 2. Heating mechanisms in GC molecular clouds.

scholarly journals 13CO(J = 1-0) Observations of the Orion Molecular Cloud

1987 ◽  
Vol 115 ◽  
pp. 149-150
Author(s):  
K. Sugitani ◽  
Y. Fukui
Keyword(s):  
Millimeter Wave ◽  
High Velocity ◽  
Molecular Cloud ◽  
High Velocity Resolution ◽  
H Ii Region ◽  
Co Emission

We present new 13CO(J = 1-0) measurements of the Orion molecular cloud. The data were taken with the 4-m millimeter-wave telescope of Nagoya University with a beamwidth of 2.7′. The high velocity resolution of 0.1 km s−1 employed has revealed significant details of the 13CO emission toward the H II region.

scholarly journals CO observations of spiral structure and the lifetime of giant molecular clouds

1979 ◽  
Vol 84 ◽  
pp. 277-283
Author(s):  
N. Z. Scoville ◽  
P. M. Solomon ◽  
D. B. Sanders
Keyword(s):  
Molecular Cloud ◽  
Mass Fraction ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Large Mass ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
The Galaxy ◽  
Co Emission ◽  
Co Observations

Observations of CO emission at ℓ=0 to 70°, |b| ≤ 1° are analyzed to give a map of the molecular cloud distribution in the galaxy as viewed from the galactic pole. From the fact that this distribution shows no obvious spiral pattern we conclude that the giant molecular clouds sampled in the CO line are situated in both arm and interarm regions and they must last more than 108 years. A similar age estimate is deduced from the large mass fraction of H2 in the interstellar medium in the interior of the galaxy. An implication of this longevity is that the great masses of these clouds may be accumulated through cloud-cloud collisions of originally smaller clouds.

CO Observations of High-Velocity Flows in the Core of the NGC 7538 Molecular Cloud

1987 ◽  
pp. 355-356
Author(s):  
Osamu Kameya ◽  
Tatsuhiko Hasegawa ◽  
Naomi Hirano ◽  
Keiya Takakubo ◽  
Munezo Seki
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
The Core ◽  
Co Observations

scholarly journals Tidally-disrupted Molecular Clouds falling to the Galactic Center

2016 ◽  
Vol 11 (S322) ◽  
pp. 115-118 ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Kenta Uehara ◽  
Ryosuke Miyawaki ◽  
Atsushi Miyazaki
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Outer Region ◽  
Recombination Line ◽  
Ionized Gas ◽  
Boundary Area ◽  
Gas Streams ◽  
Uv Emission ◽  
Sgr A

AbstractWe found a molecular cloud connecting from the outer region to the “Galactic Center Mini-spiral (GCMS)” which is a bundle of the ionized gas streams adjacent to Sgr A*. The molecular cloud has a filamentary appearance which is prominent in the CSJ=2-1 emission line and is continuously connected with the GCMS. The velocity of the molecular cloud is also continuously connected with that of the ionized gas in the GCMS observed in the H42α recombination line. The morphological and kinematic relations suggest that the molecular cloud is falling from the outer region to the vicinity of Sgr A*, being disrupted by the tidal shear of Sgr A* and ionized by UV emission from the Central Cluster. We also found the SiOJ=2-1 emission in the boundary area between the filamentary molecular cloud and the GCMS. There seems to exist shocked gas in the boundary area.

scholarly journals Collisions of supersonic clouds

2010 ◽  
Vol 6 (S270) ◽  
pp. 355-358
Author(s):  
Andrew McLeod ◽  
Jan Palouš ◽  
Anthony Whitworth
Keyword(s):  
High Velocity ◽  
Thin Shell ◽  
Molecular Clouds ◽  
Energy Equation ◽  
Low Velocity ◽  
Heating And Cooling ◽  
Non Linear ◽  
Compressed Layer

AbstractWe present simulations of supersonic collisions between molecular clouds of mass 500 M⊙ and radius 2.24 pc. The simulations are performed with the SEREN SPH code. The code treats the energy equation and the associated transport of heating and cooling radiation. The formation of protostars is captured by introducing sink particles. Low velocity collisions form a shock-compressed layer which fragments to form stars. For high-velocity collisions, υrel ⪆ 5 km s−1, the non-linear thin shell instability strongly disrupts the shock-compressed layer, and may inhibit the formation of stars.

scholarly journals Detailed 3D structure of Orion A in dust with Gaia DR2

2020 ◽  
Vol 643 ◽  
pp. A151 ◽  
Author(s):  
Sara Rezaei Kh. ◽  
Coryn A. L. Bailer-Jones ◽  
Juan D. Soler ◽  
Eleonora Zari
Keyword(s):  
Magnetic Field ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
3D Structure ◽  
Computational Cost ◽  
Mapping Technique ◽  
Wide Field ◽  
The Sun ◽  
Orion Nebula ◽  
Field Orientation

The unprecedented astrometry from Gaia’s second data release (DR2) provides us with an opportunity to study molecular clouds in the solar neighbourhood in detail. Extracting the wealth of information in these data remains a challenge, however. We have further improved our Gaussian-processes-based, three-dimensional dust mapping technique to allow us to study molecular clouds in more detail. These improvements include a significantly better scaling of the computational cost with the number of stars, and taking into account distance uncertainties to individual stars. Using Gaia DR2 astrometry together with the Two Micron All Sky Survey (2MASS) and the Wide-Field Infrared Survey Explorer (WISE) photometry for 30 000 stars, we infer the distribution of dust out to 600 pc in the direction of the Orion A molecular cloud. We identify a bubble-like structure in front of Orion A, centred at a distance of about 350 pc from the Sun. The main Orion A structure is visible at slightly larger distances, and we clearly see a tail extending over 100 pc that is curved and slightly inclined to the line of sight. The location of our foreground structure coincides with 5–10 Myr old stellar populations, suggesting a star formation episode that predates that of the Orion Nebula Cluster itself. We also identify the main structure of the Orion B molecular cloud, and in addition discover a background component to this at a distance of about 460 pc from the Sun. Finally, we associate our dust components at different distances with the plane-of-the-sky magnetic field orientation as mapped by Planck. This provides valuable information for modelling the magnetic field in three dimensions around star-forming regions.

J = 2-1 CO observations of molecular clouds with high-velocity gas - Evidence for clumpy outflows

1983 ◽  
Vol 266 ◽  
pp. 321 ◽  
Author(s):  
R. L. Plambeck ◽  
R. L. Snell ◽  
R. B. Loren
Keyword(s):  
High Velocity ◽  
Molecular Clouds ◽  
Co Observations

The Galactic Centre

1974 ◽  
Vol 60 ◽  
pp. 539-547 ◽  
Author(s):  
J. H. Oort
Keyword(s):  
Central Region ◽  
Molecular Clouds ◽  
Direct Evidence ◽  
Galactic Plane ◽  
High Rate ◽  
Small Scale ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Complicated Structure ◽  
Sgr A

The phenomena displayed by the interstellar medium in the galactic centre are considered. The asymmetries shown by the features between 1 and 3 kpc from the centre together with the presence of material lying out of the galactic plane favour the expulsion hypothesis for their origin. The nuclear disk shows a perturbation which might have resulted from such expulsion. The dense molecular clouds in the disk may well be considered as the most direct evidence that matter is expelled from the nucleus and that this occurs at a high rate. The +50 km s-1 feature in the direction of Sgr A may be the most recently expelled body of molecular gas. New observations of the central radio source, Sgr A, have revealed details on a very small scale, and the infrared core also shows a complicated structure. Probably a number of individual concentrations of gas and dust are present. While the position of the actual nucleus seems now to have been defined to within a few arcseconds, no indication has yet been found concerning its nature nor concerning the mechanism that enables it to expel the vast expanding masses of gas observed in the central region.

scholarly journals Mapping the Galactic Center

1996 ◽  
Vol 171 ◽  
pp. 369-369
Author(s):  
W.J. Duschl ◽  
S. von Linden ◽  
T. Walter ◽  
M. Wittkowski
Keyword(s):  
Angular Momentum ◽  
Molecular Clouds ◽  
Vertical Structure ◽  
Galactic Center ◽  
Galactic Plane ◽  
The Galaxy ◽  
Sgr A ◽  
Celestial Sphere ◽  
Inner Region ◽  
Galactic Longitude

Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.

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