Contributions to the theory of spiral structure. II. The density wave theory and the very hot interstellar gas component

1979 ◽  
Vol 66 (1) ◽  
pp. 121-131 ◽  
Author(s):  
M. Reinhardt ◽  
Th. Schmidt-Kaler
Keyword(s):  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Interstellar Gas ◽  
Density Wave Theory ◽  
Gas Component

scholarly journals Galactic Dynamos and Density Wave Theory

1990 ◽  
Vol 140 ◽  
pp. 135-135
Author(s):  
L Mestel ◽  
K Subramanian
Keyword(s):  
Growth Rate ◽  
Angular Velocity ◽  
Numerical Solutions ◽  
Density Wave ◽  
Wave Theory ◽  
Interstellar Gas ◽  
Global Magnetic Field ◽  
Dynamo Equation ◽  
Density Wave Theory ◽  
Image Position

A steady density wave in the stellar background of a disk–like galaxy is supposed to force a spiral shock wave in the interstellar gas. The jump in vorticity across the shock leads to a locally enhanced helicity, and so to an α–effect which is steady but azimuth–dependent in the frame rotating with the angular velocity ω of the density wave. This is simulated by the adoption of the form for the local dynamo growth rate arising when the standard kinematic dynamo equation is treated by the thin–disk approximation (Ruzmaikin et al 1988). The global magnetic field is proportional to the function Q satisfying where η is the turbulent resistivity (for simplicity assumed uniform) and is the laminar angular velocity of the gas in the inertial frame. We look for solutions of the form where is a global eigen-value, and the non-vanishing of couples all odd or all the even m-values. Anticipating that the strong differential rotation will ensure that in the modes with the largest growth-rate the higher-m parts are weak, the equations are truncated, leaving just a pair in q1, q-1, to describe a basically bisymmetric (m = 1) mode. Approximate treatment by the WKBJ technique suggests that a corotating growing mode (with Γ real and positive) will differ significantly from zero over the range between the points where Numerical solutions have been found for a set of illustrative parameters with corotation occurring at 6.67 kpc, and the turbulence parameters close to those in the M51 mode studied by Ruzmaikin et al which extends over = 1 kpc. Three growing corotating modes were found, the fastest extending for ~ 3 kpc, the other two for over 4 kpc. The first two grow 2-3 times faster, the third somewhat slower, than the M51 mode.

scholarly journals Interpretation of Observations of Spiral Structure in Terms of the Density Wave Theory

1974 ◽  
Vol 58 ◽  
pp. 399-412 ◽  
Author(s):  
Per Olof Lindblad
Keyword(s):  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Density Waves ◽  
Density Wave Theory

A review is given of recent theoretical and observational work on the density wave theory of spiral structure. Emphasis is put on the kinematic picture, and the question whether modern observations reveal the existence of density waves is discussed.

Nonlinear density wave theory for the spiral structure of galaxies

2000 ◽  
Vol 61 (5) ◽  
pp. 5710-5716 ◽  
Author(s):  
S. Kondoh ◽  
R. Teramoto ◽  
Z. Yoshida
Keyword(s):  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Density Wave Theory

scholarly journals Space Distribution and Motion of the Local HI Gas

1974 ◽  
Vol 3 ◽  
pp. 423-440 ◽  
Author(s):  
H. Weaver
Keyword(s):  
Mass Density ◽  
Density Wave ◽  
Wave Theory ◽  
Space Distribution ◽  
Cloud Formation ◽  
Interstellar Gas ◽  
Two Phase ◽  
Jeans Criterion ◽  
Density Wave Theory ◽  
Spiral Arm

In a Joint Discussion devoted to the ages and kinematics of the local stars, inclusion of a paper on the local gas may seem anomalous. There is, however, strong justification for considering such a topic. Newly formed stars retain many properties of the gas from which they originated. To understand the spatial and kinematic properties of local young stars, we must understand the spatial distribution and the kinematics of the local gas from which they were formed.A cloud within the interstellar gas can collapse gravitationally if its mass, density, and temperature satisfy the Jeans Criterion. Collapse is favored by low temperature and high density.Various investigators have pointed out that in the Lin Spiral Density Wave Theory a shock must occur on the inner edge of a spiral arm. Such a shock compresses the gas and hence promotes cloud formation with subsequent gravitational collapse to form stars. Shu and several collaborators have shown that such a shock is very effective in triggering cloud formation in a two-phase interstellar medium of the type discussed by Field et al. (1969), and it is widely believed that this is the principal step in the process of forming stars.

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