CO observations of the 30-Doradus region using SEST

10.1017/s0074180900234025 ◽

1997 ◽

Vol 170 ◽

pp. 25-32

Author(s):

Christopher F. Mckee

Keyword(s):

Mach Number ◽

Magnetic Fields ◽

Interstellar Medium ◽

Molecular Clouds ◽

Molecular Gas ◽

Wave Pressure ◽

Multiphase Structure ◽

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

The Relationship Between Gas and Cirrus Dust Filaments at the Edge of the Expanding Shell in Eridanus

10.1017/s0074180900240771 ◽

1990 ◽

Vol 139 ◽

pp. 235-236

Author(s):

G. L. Verschuur ◽

F. Verter ◽

L. J. Rickard ◽

D. T. Leisawitz

Keyword(s):

High Resolution ◽

Surface Brightness ◽

Neutral Hydrogen ◽

Scale Structure ◽

Small Scale ◽

Molecular Gas ◽

Small Scale Structure ◽

Point To Point ◽

The Relationship ◽

At the boundary of a large expanding shell in Eridanus around l = 187°, b = −50° the morphology observed in the HI emission is well mimicked by the 100 μm surface brightness but with associated structures offset by as much as 0.°5. A point-to-point comparison between I100μm and NHI in filaments of neutral hydrogen and dust (IR cirrus) produces only a weak dependence. However, when I100μm at a cirrus dust peak is compared with NHI at the associated H i peak, a relationship closer to that reported by other workers is found. Preliminary CO observations have set low limits on the molecular gas in these filaments. Since the H i and dust in our region are associated with a large expanding shell (or superbubble), shocks may be responsible for separation of gas and dust. The existence of small-scale structure in both the HI and IR is noted. We conclude that attempts to correlate HI and IR must invoke high-resolution area surveys.

The Evolution of Giant Molecular Clouds

10.1017/s0074180900072417 ◽

1980 ◽

Vol 87 ◽

pp. 137-149 ◽

Cited By ~ 1

Author(s):

Colin Norman ◽

Joseph Silk

Keyword(s):

Spatial Distribution ◽

Star Formation ◽

Molecular Clouds ◽

Supernova Remnants ◽

Density Wave ◽

Collective Effects ◽

Giant Molecular Clouds ◽

Spiral Density Wave ◽

External Galaxies ◽

We discuss the origin, lifetime, destruction, spatial distribution and relation to star formation of giant molecular clouds. A coagulation model including the effects of spiral density wave shocks is described. We explore implications for CO observations of external galaxies. The collective effects of OB star winds and supernova remnants in disrupting clouds are considered.

Search for CO in Atomic Hydrogen Clouds

10.1017/s0074180900072533 ◽

1980 ◽

Vol 87 ◽

pp. 189-190

Author(s):

I. Kazès ◽

J. Crovisier

Keyword(s):

Atomic Hydrogen ◽

Molecular Clouds ◽

Molecular Line ◽

Preliminary Results ◽

Comprehensive Search ◽

Diffuse Clouds ◽

The Relationship ◽

Absorption Features

The relationship between dense molecular clouds and diffuse clouds, as well as the mechanisms connected with the formation of molecules in diffuse clouds, may be studied using HI 21-cm line observations and molecular line observations in the same directions. For this purpose we previously studied the OH 18-cm main lines (Kazès et al., 1977) and the 2.6-mm CO lines (Crovisier and Kazès, 1977) in directions where strong 21-cm absorption features had been detected in the Nancay survey (Crovisier et al., 1978). Liszt and Burton (1979) also measured CO lines toward 19 directions observed in the Arecibo 21-cm emission/absorption survey (Dickey et al., 1978). This paper presents preliminary results of a more comprehensive search for 12CO in directions previously studied in the Nancay survey.

A Theory on the Slope of the IMF

International Astronomical Union Colloquium ◽

10.1017/s0252921100023587 ◽

1989 ◽

Vol 120 ◽

pp. 129-129

Author(s):

H. Zinnecker

Keyword(s):

Mass Spectrum ◽

Molecular Clouds ◽

Mass Relation ◽

Final Mass ◽

Co Observations ◽

The Imf

Molecular clouds are clumpy, and the mass spectrum (dN/dM) of clumps scales with the clump mass M to the -1.5 power, as determined from CO observations of molecular clouds (Blitz 1988, Stutzki et al. 1989). The basic idea is to translate the mass spectrum of clumps into a mass spectrum of stars (that are assumed to form from these clumps) by virtue of a clump-star (i.e. initial-final) mass relation.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000525 ◽

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%.

Methanol at the Edge of the Galaxy: New Observations to Constrain the Galactic Habitable Zone

The Astrophysical Journal ◽

10.3847/1538-4357/ac27a6 ◽

2021 ◽

Vol 922 (2) ◽

pp. 106

Author(s):

J. J. Bernal ◽

C. D. Sephus ◽

L. M. Ziurys

Keyword(s):

Molecular Clouds ◽

Organic Molecules ◽

Galactic Center ◽

Solar Neighborhood ◽

Habitable Zone ◽

Line Profiles ◽

Galactocentric Distance ◽

Radio Observatory ◽

The Galaxy ◽

Abstract The Galactic Habitable Zone (GHZ) is a region believed hospitable for life. To further constrain the GHZ, observations have been conducted of the J = 2 → 1 transitions of methanol (CH3OH) at 97 GHz, toward 20 molecular clouds located in the outer Galaxy (R GC = 12.9–23.5 kpc), using the 12 m telescope of the Arizona Radio Observatory. Methanol was detected in 19 out of 20 observed clouds, including sources as far as R GC = 23.5 kpc. Identification was secured by the measurement of multiple asymmetry and torsional components in the J = 2 → 1 transition, which were resolved in the narrow line profiles observed (ΔV 1/2 ∼ 1–3 km s−1). From a radiative transfer analysis, column densities for these clouds of N tot = 0.1–1.5 × 1013 cm−2 were derived, corresponding to fractional abundances, relative to H2, of f (CH3OH) ∼ 0.2–4.9 × 10−9. The analysis also indicates that these clouds are cold (T K ∼ 10–25 K) and dense (n(H2) ∼ 106 cm−3), as found from previous H2CO observations. The methanol abundances in the outer Galaxy are comparable to those observed in colder molecular clouds in the solar neighborhood. The abundance of CH3OH therefore does not appear to decrease significantly with distances from the Galactic Center, even at R GC ∼ 20–23 kpc. Furthermore, the production of methanol is apparently not affected by the decline in metallicity with galactocentric distance. These observations suggest that organic chemistry is prevalent in the outer Galaxy, and methanol and other organic molecules may serve to assess the GHZ.

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

10.1017/s0074180900014625 ◽

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 ◽

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.

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

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000015502 ◽

1978 ◽

Vol 3 (4) ◽

pp. 266-269 ◽

Cited By ~ 4

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 ◽

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.