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.

scholarly journals The rotation curve, mass, light, and velocity distribution of M31

1970 ◽  
Vol 38 ◽  
pp. 51-60
Author(s):  
J. Einasto ◽  
U. Rümmel
Keyword(s):  
Spectroscopic Data ◽  
Total Mass ◽  
Rotation Curve ◽  
Mass Density ◽  
Major Axis ◽  
Deviation Angle ◽  
Andromeda Galaxy ◽  
The Galaxy ◽  
M 31 ◽  
Central Concentration

A model for the Andromeda galaxy, M 31, has been derived from the available radio, photometric, and spectroscopic data. The model consists of four components – the nucleus, the bulge, the disc, and the flat component.For all components the following functions have been found: the mass density; the mass-to-light ratio; the velocity dispersions in three perpendicular directions (for the plane of symmetry and the axis of the galaxy); the deviation angle of the major axis of the velocity ellipsoid from the plane of symmetry; the centroid velocity (for the plane of symmetry).Our model differs in two points from the models obtained by other authors: the central concentration of mass is higher (in the nucleus the mass-to-light ratio is about 170), and the total mass of the galaxy (200 × 109 solar masses) is smaller. The differences can be explained by different rotation curves adopted, and by attributing more weight to photometric and spectroscopic data in the case of our model.

scholarly journals Outer Disc Rotation from Cepheid Variables

1996 ◽  
Vol 169 ◽  
pp. 661-667
Author(s):  
Frederic Pont ◽  
Didier Queloz ◽  
Michel Mayor ◽  
Pierre Bratschi
Keyword(s):  
Rotation Curve ◽  
Hii Regions ◽  
Radial Velocities ◽  
Classical Cepheids ◽  
The Galaxy ◽  
Cepheid Variables ◽  
Disc Rotation

We have measured radial velocities for a large number of classical cepheids of the Galaxy, particularly in the outer disc. We determine the rotation curve up to a galactocentric radius of 16 kpc. The results are then compared to similar studies using HII regions. We also consider some possible complications.

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 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 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 The Rotation Curves of Galaxies

1975 ◽  
Vol 69 ◽  
pp. 331-340 ◽  
Author(s):  
M. S. Roberts
Keyword(s):  
Rotation Curve ◽  
Mass Density ◽  
Rotational Velocity ◽  
Solar Neighborhood ◽  
Optical Measurements ◽  
H Ii Regions ◽  
Rotation Curves ◽  
Surface Mass ◽  
The Galaxy ◽  
Surface Mass Density

Currently available data on rotation curves are reviewed. For curves derived from optical measurements the distribution of the ratios: the last measured point on a rotation curve to the optical radius of the galaxy has a median value of if Reference Catalogue radii are used and if Holmberg radii are used. It is the absence of easily measurable H II regions that so severely limits the extent of these rotation curves. Accordingly, little can be said of the dependence of Vc on R for large R, where R is comparable to a Holmberg radius. The assumption that a rotation curve approaches a Keplerian curve after passing its peak rotational velocity implies a strongly concentrated and limited extent of the mass distribution within a galaxy. This assumption is not supported by 21-cm observations of the velocity field within a galaxy. Because of the greater extent of H I compared to measurable optical (blue) surface brightness, rotation curves may be defined to much larger radii from 21-cm observations. The median value of the above ratio for 14 galaxies is 1.3. At least 7 of these galaxies show an essentially constant rotational velocity at large R, while 5 galaxies have a slowly decreasing Vc(R). For both types of curves, a significant surface mass density at large R is required, and a large (≳ 100) mass-to-luminosity ratio is indicated. Such values are consistent with a late dwarf M star population (the most common type of star in the solar neighborhood) in the outer regions of a galaxy.

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