scholarly journals Selfpropagating Stochastic Star Formation and Spiral Structure

1983 ◽  
Vol 100 ◽  
pp. 141-142 ◽  
Author(s):  
J. V. Feitzinger ◽  
P. E. Seiden
Keyword(s):  
Star Formation ◽  
Spiral Structure ◽  
Relative Importance ◽  
Formation Model ◽  
Density Waves ◽  
Spiral Density Waves ◽  
Two Component ◽  
Grand Design ◽  
Dynamic Phenomena

Spiral structure in galaxies can arise from both dynamic and non dynamic phenomena: spiral density waves and stochastic selfpropagating star formation. The relative importance of these effects is still not known. Deficiences of the original selfpropagating star formation model (where only stars are taken into account) are overcome by explicitly considering the stars embedded in and interacting with a two-component gas (Seiden and Gerola, 1979; Seiden, Schulman and Feitzinger, 1982; Seiden and Gerola, 1982). The two-component gas is essential because it is the means by which we get feedback in the interaction between stars and gas. The coupling between stars and gas regulates and stabilizes star formation in a galaxy. Under proper conditions this model can give good grand design spirals (Fig. 1).

scholarly journals Star Formation in Normal Irregular Galaxies

1987 ◽  
Vol 115 ◽  
pp. 611-612
Author(s):  
Deidre A. Hunter
Keyword(s):  
Star Formation ◽  
Large Range ◽  
Density Waves ◽  
Regulatory Processes ◽  
Spiral Density Waves ◽  
Global Properties ◽  
Level Of Activity ◽  
Star Formation Activity ◽  
Irregular Galaxies

Normal, non-interacting irregular galaxies can be quite successful at forming stars. Therefore, spiral density waves are not necessary to a vigorous production of stars. Nevertheless, there is a large range in star-formation rates among irregular galaxies. Irregulars with common characteristics can have different overall levels of star-formation activity, so that the level of activity does not seem to be simple related to observable global properties of galaxian systems. The constant star formation rates of most normal irregulars also imply the existence of regulatory processes.

scholarly journals Large-scale galactic shock phenomena and the implications on star formation

1970 ◽  
Vol 38 ◽  
pp. 415-422
Author(s):  
W. W. Roberts
Keyword(s):  
Star Formation ◽  
Gravitational Collapse ◽  
Large Scale ◽  
Milky Way ◽  
Spiral Structure ◽  
Triggering Mechanism ◽  
Grand Design ◽  
Armed Spiral

The possible existence of a stationary two-armed spiral shock pattern for a disk-shaped galaxy, such as our own Milky Way System, is demonstrated. It is therefore suggested that large-scale galactic shock phenomena may very well form the large-scale triggering mechanism for the gravitational collapse of gas clouds, leading to star formation along narrow spiral arcs within a two-armed grand design of spiral structure.

scholarly journals Supernovae in Flocculent and Grand Design Galaxies

1986 ◽  
Vol 7 ◽  
pp. 585-588
Author(s):  
Marshall L. McCall ◽  
Fred H. Schmidt
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Density Wave ◽  
Type I ◽  
Type Ii ◽  
Host Galaxies ◽  
Spiral Density Waves ◽  
Grand Design

AbstractThe arm structure of supernova host galaxies has been studied in order to ascertain whether or not spiral density waves have an impact on supernovae frequencies. The ensembles of Type I and Type II supernova hosts were found to contain identical fractions of grand design spirals consistent with the representations in control samples chosen without regard to supernovae production. The results suggest that a density wave does not greatly enhance the massive star formation rate per unit luminosity of a galaxy. Instead, star formation in most galaxies may be dominated by stochastic processes.

scholarly journals The impact of spiral density waves on the star formation distribution: a view from core-collapse supernovae

2018 ◽  
pp. 379-384
Author(s):  
A. G. Karapetyan ◽  
A. A. Hakobyan ◽  
L. V. Barkhudaryan ◽  
G. A. Mamon ◽  
D. Kunth ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Large Scale ◽  
Massive Star ◽  
Core Collapse ◽  
Density Waves ◽  
Host Galaxies ◽  
Massive Star Formation ◽  
Spiral Density Waves ◽  
The Impact

We present an analysis of the impact of spiral density waves (DWs) on the radial and surface density distributions of core-collapse (CC) supernovae (SNe) in host galaxies with different arm classes. For the first time, we show that the corotation radius normalized surface density distribution of CC SNe (tracers of massive star formation) indicates a dip at corotation in long-armed grand-design (LGD) galaxies. The high SNe surface density just inside and outside corotation may be the sign of triggered massive star formation by the DWs. Our results may support the large-scale shock scenario induced by spiral DWs in LGD galaxies, which predicts a higher star formation efficiency around the shock fronts, avoiding the corotation region.

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 Dynamical Mechanisms for Discrete Unstable Spiral Modes in Galaxies

1983 ◽  
Vol 100 ◽  
pp. 119-120 ◽  
Author(s):  
Giuseppe Bertin
Keyword(s):  
Differential Rotation ◽  
Growth Rates ◽  
Spiral Structure ◽  
Long Waves ◽  
Density Waves ◽  
Physical Mechanisms ◽  
Spiral Density Waves ◽  
Propagation Properties ◽  
Normal Spiral

Progress in understanding physical mechanisms for the excitation and maintenance of spiral structure has considerably benefited from investigations of tightly wound spiral density waves (e.g., see Bertin 1980). These studies have identified the existence of four basic kinds of density waves (trailing and leading waves, and in each case short and long waves) with different propagation properties. In addition, they have led to the conclusion that some realistic galaxy models can support self-excited global normal spiral modes. These owe their maintenance to the presence of trailing waves with opposite propagation properties and are excited mostly as a result of a WASER (superreflection) mechanism at corotation. In discussing the dynamics of spiral structure and in comparing theory with observations a number of important issues should be kept in mind (Lin and Bertin 1981). Here we just recall that the calculation of spiral modes is being pursued by many researchers, using different methods. In general the structure and the growth rates of the dominant modes are determined by the radial distributions of the active disk density, the differential rotation, and the dispersion speed through the dimensionless functions εo, j, and Q (Haass, Bertin and Lin 1982).

scholarly journals Spiral patterns beyond the optical radius: numerical simulations and synthetic HI observations

2016 ◽  
Vol 11 (S321) ◽  
pp. 81-83
Author(s):  
Sergey Khoperskov ◽  
Giuseppe Bertin
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Stellar Disk ◽  
Small Scale ◽  
Density Waves ◽  
Spiral Density Waves ◽  
Hydrodynamical Simulations ◽  
Lindblad Resonance ◽  
Regular Patterns ◽  
Optical Radius

AbstractThe outer parts of many galaxy disks exhibit extended spiral arms far beyond the optical radius. To understand the nature and the origin of such outer spiral structure, we investigate the propagation in the outer gaseous regions of large-scale spiral density waves excited in the bright optical disk. By means of 3D hydrodynamical simulations, we show that spiral density waves, penetrating in the gas through the outer Lindblad resonance, can indeed give rise to relatively regular patterns outside the bright optical stellar disk. The amplitude of spiral structure increases rapidly with radius. Beyond the optical radius, spirals become nonlinear and develop small-scale features related to shear-induced instabilities. We also construct the synthetic 21-cm data cubes extracted from simulated gaseous disks. Our synthetic HI observations point to the existence of specific kinematical features related to the presence of spiral pattern perturbations that should be found in deep HI observations.

scholarly journals Density waves and star formation in grand-design spirals

2013 ◽  
Vol 560 ◽  
pp. A59 ◽  
Author(s):  
Bernabé Cedrés ◽  
Jordi Cepa ◽  
Ángel Bongiovanni ◽  
Héctor Castañeda ◽  
Miguel Sánchez-Portal ◽  
...  
Keyword(s):  
Star Formation ◽  
Density Waves ◽  
Grand Design

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.

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