Density waves in disk galaxies

1967 ◽  
Vol 31 ◽  
pp. 313-317 ◽  
Author(s):  
C. C. Lin ◽  
F. H. Shu
Keyword(s):  
Mathematical Analysis ◽  
Spiral Structure ◽  
Stellar System ◽  
Collective Modes ◽  
Disk Galaxies ◽  
Spiral Pattern ◽  
Density Waves ◽  
The Galaxy ◽  
Detailed Mathematical Analysis

Density waves in the nature of those proposed by B. Lindblad are described by detailed mathematical analysis of collective modes in a disk-like stellar system. The treatment is centered around a hypothesis of quasi-stationary spiral structure. We examine (a) the mechanism for the maintenance of this spiral pattern, and (b) its consequences on the observable features of the galaxy.

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

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 ◽  
Co Observations

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.

scholarly journals Interpretation of velocity distribution of the inner regions of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 195-199 ◽  
Author(s):  
G. de Vaucouleurs
Keyword(s):  
Velocity Distribution ◽  
Spiral Structure ◽  
The Other ◽  
Galactic Centre ◽  
Line Profiles ◽  
Spiral Pattern ◽  
Other Hand ◽  
The Galaxy

I. The large positive and negative velocities in the 21-cm line profiles near the galactic centre have indicated the presence of substantial departures from circular motions in the central parts of the Galaxy. The Leiden astronomers (Oort and Rougoor 1958; Rougoor and Oort 1960) have interpreted these observations in terms of an “expanding arm” at a mean distance of about 3 kpc from the centre. It is not clear how these arms or arcs are related to the regular spiral structure, if the Galaxy is an ordinary spiral similar to M31 as commonly assumed. If, on the other hand, the Galaxy is similar to the SAB(r) or SAB(rs) systems, as suggested by the multiplicity of the spiral pattern discussed in another communication, a different interpretation of the velocity distribution is possible.

scholarly journals Numerical Experiments on the Response Mechanism of Barred Spirals

1983 ◽  
Vol 100 ◽  
pp. 207-208
Author(s):  
K. O. Thielheim ◽  
H. Wolff
Keyword(s):  
Numerical Experiments ◽  
Spiral Structure ◽  
Stellar Disk ◽  
Disk Galaxies ◽  
Density Waves ◽  
First Order ◽  
Spiral Density Waves ◽  
Stellar Component ◽  
Spiral Structures ◽  
Self Gravity

As a generating mechanism of spiral structure, we have recently studied the driving of density waves in the stellar component of disk galaxies by growing barlike perturbations or oval distortions. Numerical experiments (Thielheim and Wolff 1981, 1982) as well as analytical calculations using the first-order epicyclic approximation (Thielheim 1981; Thielheim and Wolff 1982) have been performed, demonstrating that this mechanism is capable of producing two-armed trailing spiral density waves in disks of noninteracting stars. These regular, global spiral structures are similar to those found in N-body experiments on self-consistent stellar disks that show bar instabilities which are weak enough to allow spiral patterns to persist (e.g., Hohl 1978; Berman and Mark 1979; Sellwood 1981). On account of this similarity, we take the view that the spiral structure observed in N-body experiments is primarily not an effect of the self-gravity of the stellar disk but a response phenomenon, caused by the formation of a weak central bar and its subsequent growth due to angular momentum extraction by interaction with the spiral as described by Lynden-Bell and Kalnajs (1972).

scholarly journals Stability of a Collisionless Stellar Disk

1996 ◽  
Vol 169 ◽  
pp. 519-520
Author(s):  
E. Griv
Keyword(s):  
Asymptotic Analysis ◽  
Spiral Structure ◽  
Stellar Disk ◽  
Spiral Pattern ◽  
Density Waves ◽  
Collective Effect ◽  
Modal Theory

The study of stability of the stellar disks of flat galaxies is the first step towards an understanding of the phenomena of spiral structure. To explain the spiral pattern, Lin and Shu (1964) further developed the Lindblad's idea of density waves by considering the spiral structure as the collective effect in a self-gravitating system. As an extension to the original Lin-Shu theory, unstable spiral modes have been obtained from an asymptotic analysis (e.g., Bertin [1980]). In such “modal theory”, the Jeans-type instability (even weak) is important to the maintenance of spiral structure.

Modeling the Evolution of Disk Galaxies. I. The Chemodynamical Method and the Galaxy Model

1997 ◽  
Vol 476 (2) ◽  
pp. 544-559 ◽  
Author(s):  
M. Samland ◽  
G. Hensler ◽  
Ch. Theis
Keyword(s):  
Disk Galaxies ◽  
The Galaxy ◽  
Galaxy Model

scholarly journals Structural Health Monitoring of 2D Plane Structures

2021 ◽  
Vol 11 (5) ◽  
pp. 2000
Author(s):  
Behnam Mobaraki ◽  
Haiying Ma ◽  
Jose Antonio Lozano Galant ◽  
Jose Turmo
Keyword(s):  
Mechanical Properties ◽  
Health Monitoring ◽  
Mathematical Analysis ◽  
Stiffness Matrix ◽  
State Of The Art ◽  
System Of Equations ◽  
Matrix System ◽  
Structural System ◽  
Detailed Mathematical Analysis ◽  
Structural System Identification

This paper presents the application of the observability technique for the structural system identification of 2D models. Unlike previous applications of this method, unknown variables appear both in the numerator and the denominator of the stiffness matrix system, making the problem non-linear and impossible to solve. To fill this gap, new changes in variables are proposed to linearize the system of equations. In addition, to illustrate the application of the proposed procedure into the observability method, a detailed mathematical analysis is presented. Finally, to validate the applicability of the method, the mechanical properties of a state-of-the-art plate are numerically determined.

scholarly journals On the maintenance of spiral structure

1979 ◽  
Vol 84 ◽  
pp. 151-153
Author(s):  
James W-K. Mark ◽  
Linda Sugiyama ◽  
Robert H. Berman ◽  
Giuseppe Bertin
Keyword(s):  
Spiral Structure ◽  
Travelling Waves ◽  
Integral Condition ◽  
Stimulated Emission ◽  
Stellar Disk ◽  
Wave System ◽  
Wave Amplification ◽  
Corotation Radius ◽  
The Galaxy ◽  
Central Regions

A concentrated nuclear bulge with about 30% of the galaxy mass is sufficient (Lin, 1975; Berman and Mark, 1978) to eliminate strong bar-forming instabilities which dominate the dynamics of the stellar disk. Weak bar-like or oval distortions might remain depending on the model. In such systems self-excited discrete modes give rise to global spiral patterns which are maintained in the presence of differential rotation and dissipation (cf. especially the spiral patterns in Bertin et al., 1977, 1978). These spiral modes are standing waves that are physically analyzable (Mark, 1977) into a superposition of two travelling waves propagating in opposite directions back and forth between galactic central regions and corotation (a resonator). Only a few discrete pattern frequencies are allowed. An interpretation is that the central regions and corotation radius must be sufficiently far apart so that a Bohr-Sommerfeld type of phase-integral condition is satisfied for the wave system of each mode. The temporal growth of these modes is mostly due to an effect of Wave Amplification by Stimulated Emission (of Rotating Spirals, abbrev. WASERS, cf. Mark 1976) which occurs in the vicinity of corotation. In some galaxies one mode might be predominent while other galaxies could exhibit more complicated spiral structure because several modes are present. Weak barlike or oval distortions hardly interfere with the structure of these modes. But they might nevertheless contribute partially towards strengthening the growth of one mode relative to another, as well as affecting the kinematics of the gaseous component.

scholarly journals Evidence for azimuthal variations of the oxygen-abundance gradient tracing the spiral structure of the galaxy HCG 91c

2017 ◽  
Vol 601 ◽  
pp. A61 ◽  
Author(s):  
F. P. A. Vogt ◽  
E. Pérez ◽  
M. A. Dopita ◽  
L. Verdes-Montenegro ◽  
S. Borthakur
Keyword(s):  
Spiral Structure ◽  
Oxygen Abundance ◽  
Abundance Gradient ◽  
The Galaxy
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