scholarly journals Gas Response to a Rotating Stellar Bar

1978 ◽  
Vol 3 (3) ◽  
pp. 234-236
Author(s):  
M. P. Schwarz
Keyword(s):  
Spiral Galaxies ◽  
Fast Rate ◽  
Density Wave ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Spiral Waves ◽  
Galactic Rotation ◽  
Spiral Pattern ◽  
Density Wave Theory ◽  
Gas Response

The arms in spiral galaxies cannot be material arms for then they would wind up on a time scale of one galactic rotation, or a few times 108 years. The large number of spirals suggests that the spiral pattern must persist for about 1010 years (or be continually rejuvenated). The density wave theory treats the spiral pattern as a wave phenomenon, thus overcoming this problem. Much work has been done studying small amplitude oscillations in flat stellar discs. Self-consistent spiral modes have been found, but they are not stable and grow at a fast rate. Numerical simulations of thin stellar discs, such as those of Hohl (1971), which can handle finite amplitude waves, have been more successful. Spiral waves form initially but evolve into a steady state rotating bar. It seems therefore, that a long-lived spiral cannot be formed in stars alone.

scholarly journals Signatures of long-lived spiral patterns: The color gradient trend

2012 ◽  
Vol 10 (H16) ◽  
pp. 323-323
Author(s):  
Eric E. Martínez-García ◽  
Rosa Amelia González-Lópezlira
Keyword(s):  
Stellar Population ◽  
Density Wave ◽  
Wave Theory ◽  
Disk Galaxies ◽  
Population Synthesis ◽  
Spiral Pattern ◽  
Stellar Population Synthesis ◽  
Color Gradient ◽  
Pattern Speeds ◽  
Density Wave Theory

AbstractBased both on observations and simulations, recent works propose that the speed of the spiral pattern in disk galaxies may decrease with increasing radius; the implications are that patterns are actually short-lived, and that the azimuthal color/age gradients across spiral arms predicted by density wave theory could not be produced. We, however, have consistently found such gradients, and measured spiral pattern speeds by comparing the observations with stellar population synthesis models (González & Graham 1996; Martínez-García et al. 2009a, b; Martínez-García & González-Lópezlira 2011). Here, we summarize our previous results in non-barred and weakly barred spirals, together with six new, as yet unpublished, objects. On the other hand, we have indeed found a trend whereby pattern speeds at smaller radii are larger than expected from a model that assumes purely circular orbits (cf. Figure 1), likely due to the effect of spiral shocks on the orbits of newborn stars. The results suggest that spirals may behave as steady long-lived patterns.

Density wave theory and the classification of spiral galaxies

1975 ◽  
Vol 196 ◽  
pp. 381 ◽  
Author(s):  
W. W., Jr. Roberts ◽  
M. S. Roberts ◽  
F. H. Shu
Keyword(s):  
Spiral Galaxies ◽  
Density Wave ◽  
Wave Theory ◽  
Density Wave Theory

scholarly journals Neutral hydrogen in the Sagittarius and Scutum spiral arms

1970 ◽  
Vol 38 ◽  
pp. 397-414 ◽  
Author(s):  
W. B. Burton ◽  
W. W. Shane
Keyword(s):  
Large Scale ◽  
Galactic Center ◽  
Density Wave ◽  
Neutral Hydrogen ◽  
Wave Theory ◽  
Galactic Rotation ◽  
Circular Rotation ◽  
Kinematic Models ◽  
Density Wave Theory ◽  
Galactic Longitude

Observations of the neutral hydrogen in the first quadrant of galactic longitude have been analysed. The existence of large-scale streaming motions such as the streaming associated with the Sagittarius arm makes interpretation of the observations in terms of circular galactic rotation unsatisfactory. It is shown that application of the density-wave theory formulated by Lin et al. (1969) leads to a more satisfactory interpretation. Using kinematic models based on this theory the distribution and motion of the neutral hydrogen are studied. Failures of kinematic models based on circular rotation are pointed out. A map of the distribution of neutral hydrogen is produced. The Scutum arm is composed of inner and outer arcs both of which seem to be moving outward from the galactic center with velocities of the order of 30 km s−1.

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 Rotation curves of high-luminosity spiral galaxies and the rotation curve of our galaxy

1979 ◽  
Vol 84 ◽  
pp. 211-220 ◽  
Author(s):  
Vera C. Rubin
Keyword(s):  
Rotation Curve ◽  
Spiral Galaxies ◽  
Rotational Velocity ◽  
Density Wave ◽  
Wave Theory ◽  
High Luminosity ◽  
Rotation Curves ◽  
Flat Rotation Curve ◽  
Density Wave Theory ◽  
Spiral Arm

Rotation curves of high luminosity spiral galaxies are flat, to distances as great as r=49 kpc. This implies a significant mass at large r. Rotational velocities increase about 20 km/s across a spiral arm, as predicted by the density wave theory. By analogy, it is suggested that our Galaxy has a flat rotation curve out to r∼60 kpc, with V ∼ constant at near the solar rotational velocity, and m ∼7×1011 m⊙. Values of A and B imply that the sun is not located in a spiral arm.

scholarly journals The evolution of pitch angles of spiral arms

2019 ◽  
Vol 490 (1) ◽  
pp. 1470-1473 ◽  
Author(s):  
J E Pringle ◽  
C L Dobbs
Keyword(s):  
Pitch Angle ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Spiral Arms ◽  
First Approximation ◽  
Density Wave Theory ◽  
Self Gravity ◽  
Random Times

ABSTRACTIn spiral galaxies, the pitch angle, α, of the spiral arms is often proposed as a discriminator between theories for the formation of the spiral structure. In Lin–Shu density wave theory, α stays constant in time, being simply a property of the underlying galaxy. In other theories (e.g. tidal interaction, and self-gravity), it is expected that the arms wind up in time, so that to a first approximation $\cot \alpha \propto t$. For these theories, it would be expected that a sample of galaxies observed at random times should show a uniform distribution of $\cot \alpha$. We show that a recent set of measurements of spiral pitch angles (Yu & Ho) is broadly consistent with this expectation.

scholarly journals Possible Pattern Speeds of a Density Wave in our Galaxy

1977 ◽  
Vol 45 ◽  
pp. 279-282 ◽  
Author(s):  
Preben J. Grosbøl
Keyword(s):  
Velocity Field ◽  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Young Stars ◽  
Spiral Pattern ◽  
Considerable Effort ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Density Wave Theory

Since the density wave theory was introduced by Lin and Shu (1964) to explain the spiral structure considerable effort has been made to detect this kind of wave in our galaxy and to determine its parameters. Observations of the distribution and velocity field of gas and young objects show the present shape and location of the spiral pattern in our galaxy but tell little about its angular velocity. It was proposed by Strömgren (1967) to estimate this important parameter by calculating the places of formation of moderately young stars for which accurate space velocities and ages are known. This was done assuming that the majority of stars is formed in spiral arms so that the stellar birthplaces would outline the position of the spiral pattern at different epochs. Later, Yuan (1969) and Wielen (1973) calculated stellar birthplaces in the spiral potential given by Lin et al. (1969). These investigations showed no disagreement with the assumed density wave, however, the number of stars was too small to verify the assumed pattern speed.

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