Mapping Neutral Hydrogen in External Galaxies

1974 ◽  
pp. 291-319 ◽  
Author(s):  
Melvyn C. H. Wright
Keyword(s):  
Neutral Hydrogen ◽  
External Galaxies

scholarly journals Spiral structure of the Galaxy Derived from the Hat Creek survey of neutral hydrogen

1970 ◽  
Vol 38 ◽  
pp. 126-139 ◽  
Author(s):  
H. Weaver
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
The Sun ◽  
General Picture ◽  
Contour Maps ◽  
The Galaxy ◽  
External Galaxies ◽  
Perseus Arm ◽  
Spiral Arm

The extensive Hat Creek survey of neutral hydrogen combined with southern observations provides the basis for a new discussion of the spiral structure of the galaxy. The purpose of this investigation is to provide a general picture of the galaxy. It is found that the pitch of the spiral arms is approximately 12°.5 and that there are many spurs and interarm features as we observe in external galaxies.The sun is not located in a major spiral arm, but rather in a spur or offshoot originating near or at the Sagittarius arm, which is a major structure in the galaxy. The young stars in the general vicinity of the sun delineate this spur, not a major arm structure. The stars and the gas are in agreement in indicating a large pitch angle (20°–25°) for this local structure, which differs from the smaller pitch angle for the arms which form the system as a whole.In the presentation a computer-produced movie of the galaxy based on Hat Creek hydrogen contour maps similar to those in Figure 1 was shown. It was used to illustrate generally the complexity of the gas structure and, in particular, to show (i) observational aspects of the spur in which the sun is located and (ii) the point of origin of the so-called Perseus arm.

scholarly journals Extragalactic Diffuse Interstellar Bands: A Universal Problem

2013 ◽  
Vol 9 (S297) ◽  
pp. 41-50 ◽  
Author(s):  
M. A. Cordiner
Keyword(s):  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Diffuse Interstellar Bands ◽  
History Of ◽  
External Galaxies ◽  
Increased Sensitivity ◽  
Low Metallicity ◽  
The 1960S ◽  
Large Telescopes

AbstractThe first extragalactic diffuse interstellar band (DIB) detections were of λ4430 in the Large and Small Magellanic Clouds (LMC and SMC) in the 1960s and 70s. Driven mainly by the increased sensitivity afforded by 8-10 m-class telescopes, the last 13 years have witnessed an explosion of DIB discoveries throughout the nearby and distant universe. This review focuses on the history of extragalactic DIB studies, including some of the important results that have come out of this field, and looks to the future for what can be learned about DIBs in external galaxies with the next generation of large telescopes. So far, DIBs have been observed in the Magellanic Clouds, starburst galaxies, DLAs, and nearby (≤30 Mpc distant) spiral galaxies, and are found to be ubiquitous in the diffuse interstellar medium (ISM) of extragalactic environments wherever dust is present. Important results include the finding that DIB carriers are significantly more closely related to dust than to neutral hydrogen, and that the λ6283 DIB tends to be anomalously weak in low-metallicity sightlines.

scholarly journals Small-scale Properties of HI in Nearby Galaxies

1991 ◽  
Vol 144 ◽  
pp. 213-222
Author(s):  
Robert Braun
Keyword(s):  
Energy Deposition ◽  
Neutral Hydrogen ◽  
Shell Structures ◽  
Great Promise ◽  
Small Scale ◽  
Hard Constraints ◽  
Absorption Studies ◽  
External Galaxies ◽  
Nearby Galaxies ◽  
Scale Properties

The instrumental requirements and current observational results are outlined for the study of resolved neutral hydrogen structures in both emission and absorption in external galaxies. Neutral super-shell structures exterior to ionized shells around OB associations seem to be a common phenomenon. Further analysis of existing data should allow quantification of the degree and rate of energy deposition in the ISM by massive stars. HI absorption studies offer great promise in constraining the physical properties of the neutral ISM, including an estimate of the gas pressure. Together these data will provide hard constraints on the existence and prevalence of chimney formation, and hence disk – halo interactions in a variety of galactic environments.

An Interferometric Investigation of the Spatial Distribution and Motion of the Neutral Hydrogen in Seven External Galaxies.

1965 ◽  
Vol 70 ◽  
pp. 147
Author(s):  
G. A. Seielstad ◽  
J. B. Whiteoak ◽  
V. Radhakrishnan ◽  
E. B. Fomalont
Keyword(s):  
Spatial Distribution ◽  
Neutral Hydrogen ◽  
External Galaxies ◽  
Interferometric Investigation

Motions of neutral hydrogen at high latitudes

1967 ◽  
Vol 31 ◽  
pp. 265-278 ◽  
Author(s):  
A. Blaauw ◽  
I. Fejes ◽  
C. R. Tolbert ◽  
A. N. M. Hulsbosch ◽  
E. Raimond
Keyword(s):  
Surface Density ◽  
Velocity Dispersion ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
High Latitudes ◽  
Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° <l< 250°, + 40° <b< + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| < 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

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