scholarly journals Connecting interacting galaxies with manifolds

2016 ◽  
Vol 11 (S321) ◽  
pp. 128-128
Author(s):  
M. Romero-Gomez ◽  
E. Athanassoula
Keyword(s):  
Circular Orbit ◽  
Invariant Manifolds ◽  
Point Of View ◽  
Interacting Galaxies ◽  
Disk Galaxies ◽  
Lagrangian Points ◽  
Spiral Arms ◽  
Lyapunov Orbits ◽  
Galactic System

AbstractIt is well known that the interaction between two disk galaxies generates tidal spiral arms and a connection in the form of a bridge. Here we address the question of the formation of tidal arms and bridges from a dynamical point of view. We model the bridges and tails observed in interacting galaxies using the invariant manifolds associated to the Lyapunov orbits of the Lagrangian points of the galactic system, when the two galaxies are considered as two point masses in a circular orbit.

scholarly journals GEOMETRY OF HOMOCLINIC CONNECTIONS IN A PLANAR CIRCULAR RESTRICTED THREE-BODY PROBLEM

2007 ◽  
Vol 17 (04) ◽  
pp. 1151-1169 ◽  
Author(s):  
MARIAN GIDEA ◽  
JOSEP J. MASDEMONT
Keyword(s):  
Symbolic Dynamics ◽  
Body Problem ◽  
Invariant Manifolds ◽  
Libration Point ◽  
Homoclinic Orbits ◽  
Restricted Three Body Problem ◽  
Three Body Problem ◽  
Lyapunov Orbits ◽  
Homoclinic Connections ◽  
Three Body

The stable and unstable invariant manifolds associated with Lyapunov orbits about the libration point L1between the primaries in the planar circular restricted three-body problem with equal masses are considered. The behavior of the intersections of these invariant manifolds for values of the energy between that of L1and the other collinear libration points L2, L3is studied using symbolic dynamics. Homoclinic orbits are classified according to the number of turns about the primaries.

Dynamical imprint of interstellar gas on persistence of spiral structure in galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 296-297
Author(s):  
Soumavo Ghosh ◽  
Chanda J. Jog
Keyword(s):  
Time Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Disk Galaxies ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
Pattern Speed

AbstractThe persistence of the spiral structure in disk galaxies has long been debated. In this work, we investigate the dynamical influence of interstellar gas on the persistence of the spiral arms in disk galaxies. We show that the gas helps the spiral arms to survive for longer time-scale (~ a few Gyr). Also, we show that the addition of gas in calculation is necessary for getting a stable density wave corresponding to the observed pattern speed of the spiral arms.

scholarly journals Classification of rough transformations of a circle from a modern point of view

2018 ◽  
Vol 20 (4) ◽  
pp. 408-418
Author(s):  
A. E. Kolobyanina ◽  
E. V. Nozdrinova ◽  
O. V. Pochinka
Keyword(s):  
Invariant Manifolds ◽  
Sufficient Conditions ◽  
Periodic Points ◽  
Point Of View ◽  
Topological Classification ◽  
Topological Invariants ◽  
Modern Theory ◽  
Ambient Manifold ◽  
Periodic Data

In this paper the authors use modern methods and approaches to present a solution to the problem of the topological classification of circle’s rough transformations in canonical formulation. In the modern theory of dynamical systems such problems are understood as the complete topological classification: finding topological invariants, proving the completeness of the set of invariants found and constructing a standard representative from a given set of topological invariants. Namely, in the first theorem of this paper the type of periodic data of circle’s rough transformations is established. In the second theorem necessary and sufficient conditions of their conjugacy are proved. These conditions mean coincidence of periodic data and rotation numbers. In the third theorem the admissible set of parameters is implemented by a rough transformation of a circle. While proving the theorems, we assume that the results on the local topological classification of hyperbolic periodic points, as well as the results on the global representation of the ambient manifold as a union of invariant manifolds of periodic points, are known.

scholarly journals Dynamical Friction in Disk Galaxies: The Radial Dependence

1996 ◽  
Vol 157 ◽  
pp. 372-374
Author(s):  
Mattias Wahde ◽  
Karl Johan Donner
Keyword(s):  
Numerical Simulations ◽  
Decay Time ◽  
Circular Orbit ◽  
Simple Formula ◽  
Radial Dependence ◽  
Disk Galaxies ◽  
Dynamical Friction ◽  
Satellite Galaxy ◽  
Parent Galaxy ◽  
Good Agreement

AbstractA simple formula is derived for the force of dynamical friction acting on a satellite galaxy which is moving on a nearly circular orbit around its parent galaxy. Using this formula, estimates of the decay time are computed. The results are then compared with the corresponding results from numerical simulations, and are found to be in good agreement.

scholarly journals 33. Structure and Dynamics of the Galactic System

1976 ◽  
Vol 16 (3) ◽  
pp. 37-72
Author(s):  
L. Perek
Keyword(s):  
High Latitude ◽  
Galactic Halo ◽  
Point Of View ◽  
Structure And Dynamics ◽  
Galactic System

It has become a tradition for Commission 33 to invite several authors to contribute to the Report. The scope of the Commission is so wide that it is beyond the possibilities of any one individual to do this work without assistance. B. Westerlund contributed Section 2, S. W. McCuskey Sections 3 and 4, T. Elvius the paragraph on high-latitude studies, F. J. Kerr Sections 3, 4 and 5B, J. Einasto Sections 6B and D, and a summary of the current research by Soviet astronomers, K. C. Freeman Sections 6C, E. L. Woltjer Section 6F, and L. Perek Sections 1, 5A, and 6A. Section 6B contains this time a paragraph on the Galactic Corona as seen from the point of view of galactic models, while Section 4 contains a paragraph on the structure of the Galactic Halo.

scholarly journals Outer spiral structure in disk galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 123-123
Author(s):  
P.A. Patsis
Keyword(s):  
Periodic Orbits ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Disk Galaxies ◽  
Spiral Arms ◽  
Chaotic Orbits ◽  
Grand Design ◽  
Pattern Speed ◽  
Spiral Structures ◽  
Barred Spiral Galaxies

AbstractIn several grand design barred-spiral galaxies it is observed a second, fainter, outer set of spiral arms. Typical examples of objects of this morphology can be considered NGC 1566 and NGC 5248. I suggest that such an overall structure can be the result of two dynamical mechanisms acting in the disc. The bar and both spiral systems rotate with the same pattern speed. The inner spiral is reinforced by regular orbits trapped around the stable, elliptical, periodic orbits of the central family, while the outer system of spiral arms is supported by chaotic orbits. Chaotic orbits are also responsible for a rhomboidal area surrounding the inner barred-spiral region. In general there is a discontinuity between the two spiral structures at the corotation region.

scholarly journals Quantifying the fine structures of disk galaxies with deep learning: Segmentation of spiral arms in different Hubble types

2021 ◽  
Vol 647 ◽  
pp. A120
Author(s):  
K. Bekki
Keyword(s):  
Deep Learning ◽  
Galaxy Evolution ◽  
Training Data ◽  
Disk Galaxies ◽  
Data Sets ◽  
Giant Molecular Clouds ◽  
Spatial Correlations ◽  
Spiral Arms ◽  
Constant Pitch ◽  
Hydrodynamical Simulations

Context. Spatial correlations between spiral arms and other galactic components such as giant molecular clouds and massive OB stars suggest that spiral arms can play vital roles in various aspects of disk galaxy evolution. Segmentation of spiral arms in disk galaxies is therefore a key task when these correlations are to be investigated. Aims. We therefore decomposed disk galaxies into spiral and nonspiral regions using the code U-Net, which is based on deep-learning algorithms and has been invented for segmentation tasks in biology. Methods. We first trained this U-Net with a large number of synthesized images of disk galaxies with known properties of symmetric spiral arms with radially constant pitch angles and then tested it with entirely unknown data sets. The synthesized images were generated from mathematical models of disk galaxies with various properties of spiral arms, bars, and rings in these supervised-learning tasks. We also applied the trained U-Net to spiral galaxy images synthesized from the results of long-term hydrodynamical simulations of disk galaxies with nonsymmetric spiral arms. Results. We find that U-Net can predict the precise locations of spiral arms with an average prediction accuracy (Fm) of 98%. We also find that Fm does not depend strongly on the numbers of spiral arms, presence or absence of stellar bars and rings, and bulge-to-disk ratios in disk galaxies. These results imply that U-Net is a very useful tool for identifying the locations of spirals arms. However, we find that the U-Net trained on these symmetric spiral arm images cannot predict entirly unknown data sets with the same accuracy that were produced from the results of hydrodynamical simulations of disk galaxies with nonsymmetric irregular spirals and their nonconstant pitch angles across disks. In particular, weak spiral arms in barred-disk galaxies are properly segmented. Conclusions. These results suggest that U-Net can segment more symmetric spiral arms with constant pitch angles in disk galaxies. However, we need to train U-Net with a larger number of more realistic galaxy images with noise, nonsymmetric spirals, and different pitch angles between different arms in order to apply it to real spiral galaxies. It would be a challenge to make a large number of training data sets for such realistic nonsymmetric and irregular spiral arms with nonconstant pitch angles.

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