scholarly journals Neutral hydrogen in the central part of the galactic system

1959 ◽  
Vol 9 ◽  
pp. 416-422 ◽  
Author(s):  
G. W. Rougoor ◽  
J. H. Oort
Keyword(s):  
Rotation Curve ◽  
Neutral Hydrogen ◽  
Line Profiles ◽  
Rotational Model ◽  
Galactic System ◽  
The Galaxy

While trying to determine the rotation curve in 1953 Kwee, Muller, and Westerhout [1] found long and faint wings in the line profiles within 20 to 25 degrees longitude from the center. The gas responsible for these wings should therefore lie within 3 kiloparsecs from the center. The velocities of the neutral hydrogen causing these wings are far greater than could be expected on the basis of a reasonable rotational model of the Galaxy. Therefore, the wings were tentatively interpreted as being caused by high turbulent velocities in the gas. In view of the new and better data obtained with the 25-meter telescope in Dwingeloo, this interpretation has now been dropped. The new conclusion is that all of the neutral hydrogen in these regions is expanding and at the same time taking part in the galactic rotation. The evidence for this conclusion will be briefly presented.

scholarly journals 21 cm Observations of NGC 45

1972 ◽  
Vol 25 (3) ◽  
pp. 315 ◽  
Author(s):  
BM Lewis
Keyword(s):  
Radio Telescope ◽  
Rotation Curve ◽  
Neutral Hydrogen ◽  
Order Effects ◽  
Line Profiles ◽  
First Order ◽  
Consistent Model ◽  
Self Consistent

Observations of NGC 45 have been made at a wavelength of 21 cm using the radio telescope at Parkes. Line profiles have been measured for a grid of 44 points spaced at intervals of 6' arc. From the measurements the mass of neutral hydrogen is calculated to be 8�2 � 108 M?, assuming a distance of 3 Mpc. A simple self-consistent model is determined by computing line profiles to compare directly with the observations. This enables the rotation curve to be corrected for the first-order effects of beam smoothing and results in a total limiting mass of 2�5 � 1010 M?.

scholarly journals Theoretical Considerations on the Dynamics of Normal Galactic Nuclei

1980 ◽  
Vol 5 ◽  
pp. 197-204
Author(s):  
Robert H. Sanders
Keyword(s):  
Spatial Distribution ◽  
Gravitational Field ◽  
Mass Distribution ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
The Galaxy ◽  
Theoretical Considerations ◽  
Normal Spiral

I want to discuss the origin of non-circular gas motions observed in the nuclei of normal spiral galaxies and the possibility that recurring violent activity in normal nuclei excites such motion. But first, let us review several basic aspects of the nearest normal galactic nucleus — the nucleus of our own Galaxy.The rotation curve as observed in the 21-cm line of neutral hydrogen gives some indication of the form of the gravitational field in the central region of the Galaxy. Figure 1 is a smooth fit to the rotation curve in the inner few kiloparsecs (solid line) taken essentially from the data of Rougoor and Oort (1960) and Simonson and Mader (1973). This rotation curve, within 1 kpc of the centre, is completely accounted for by the mass distribution implied by the extended 2.2-μ emission (Becklin and Neugebauer 1968, Oort 1971). Moreover, there is little doubt that this centrally condensed mass distribution should be identified with the bulge or spheroidal component of the Galaxy, because the spatial distribution of the 2.2-μ intensity is practically identical to the distribution of visible starlight in the bulge of M31 (Sandage, Becklin, and Neugebauer 1969). The conclusion is that the bulge overwhelmingly dominates the gravitational field inside of 1 kpc.

scholarly journals Theoretical 21-cm line profiles: Comparison with observations

1970 ◽  
Vol 38 ◽  
pp. 391-396 ◽  
Author(s):  
C. Yuan
Keyword(s):  
Galactic Plane ◽  
Density Wave ◽  
Neutral Hydrogen ◽  
Wave Theory ◽  
Line Profiles ◽  
Spiral Pattern ◽  
The Galaxy ◽  
Density Wave Theory ◽  
Good Agreement

In order to make a direct comparison with observations of the 21-cm line of neutral hydrogen, theoretical profiles based on the ideas of the density-wave theory are constructed for a modified Schmidt model of the Galaxy and its theoretical spiral pattern. The comparison has covered galactic longitudes lII = 30° −330° with 10° intervals in the galactic plane. Good agreement is found in most of the above directions.

scholarly journals Radial velocities of neutral hydrogen in the anticenter region of the Galaxy

1970 ◽  
Vol 38 ◽  
pp. 164-168 ◽  
Author(s):  
L. Velden
Keyword(s):  
Emission Line ◽  
Statistical Method ◽  
Neutral Hydrogen ◽  
Radial Velocities ◽  
Line Profiles ◽  
Interstellar Gas ◽  
Observational Material ◽  
Circular Rotation ◽  
The Galaxy

An observational material of 21-cm H I emission-line profiles is investigated by a statistical method to derive the kinematical properties of the interstellar gas in the region of the galactic anticenter. A description of the method used as well as the results obtained, concerning deviations from a circular rotation, are given.

scholarly journals The Three-Dimensional Distribution of Neutral Hydrogen in M31

1978 ◽  
Vol 77 ◽  
pp. 175-181
Author(s):  
Robert N. Whitehurst ◽  
Morton S. Roberts ◽  
Thomas R. Cram
Keyword(s):  
Rotation Curve ◽  
Three Dimensional ◽  
Neutral Hydrogen ◽  
Preceding Paper ◽  
Systematic Procedure ◽  
Out Of Plane ◽  
The Galaxy ◽  
Dimensional Distribution

Given the wealth of data, the rotation curve, and the necessity for out-of-plane hydrogen demonstrated in the preceding paper, it seems desirable to attempt to establish a systematic procedure for determining the three-dimensional distribution of hydrogen. Under the assumption of cylindrical rotation this is, in principle, possible for most of the galaxy.

scholarly journals Neutral Hydrogen In The Irregular Galaxy Ngc 3Lo9

1966 ◽  
Vol 19 (5) ◽  
pp. 687 ◽  
Keyword(s):  
Radio Telescope ◽  
Total Mass ◽  
Rotation Curve ◽  
Neutral Hydrogen ◽  
Irregular Galaxy ◽  
The Galaxy

The galaxy NGC 3109 was investigated at 21 cm wavelength with the 210 ft radio telescope at Parkes. For a distance d = 2�2 Mpc the total mass of neutral hydrogen is MH = 2�2 X 109 M0 (corrected for self-absorption). The rotation curve has been determined

scholarly journals A comparison of dynamical models of the Andromeda Nebula and the Galaxy

1970 ◽  
Vol 38 ◽  
pp. 61-68
Author(s):  
V. C. Rubin ◽  
W. K. Ford
Keyword(s):  
Rotation Curve ◽  
Neutral Hydrogen ◽  
Radial Velocities ◽  
H Ii Regions ◽  
Dynamical Models ◽  
Mass Model ◽  
The Galaxy ◽  
Andromeda Nebula ◽  
M 31

(1) From new radial velocities of 67 H II regions in M 31, rotational velocities and a mass model of M 31 are derived, and compared with the rotation curve and Schmidt mass model of our galaxy. (2) It is shown that in M 31 the distribution of H II regions as identified by Baade agrees with the distribution of neutral hydrogen determined from 21-cm observations. Also, the rotation curve derived from the H II velocities outside of the nucleus is similar to the rotation curve derived from 21-cm H I observations.

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.

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