Galactic Rings

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Article Contents

1.Introduction
2.Historical Overview
2.1 Inner Ring Structures
2.2 Outer Ring Structures
2.3 Nuclear Ring Structures
3.Comparison of Ring Classifications
4.Recent Revisions to the Classification
4.1 Outer Ring and Pseudoring Morphologies
4.2 Inner, Outer, and Nuclear Lenses
5.Confusion of Ring Types in Nonbarred Galaxies
6.Summary of Notation for Ring and Lens Types
7.Rings and Lenses as Distinct Components of Barred Galaxy Structure
8.Rings and Nuclear Activity
9.Observations of Galactic Rings
9.1 Frequency
9.2 Linear and Relative Diameters
9.3 Intrinsic Shapes and Orientations
9.4 Photometric Properties
9.5 HII Regions in Ringed Galaxies
9.6 Neutral Hydrogen Emission from Ringed Galaxies
9.7 CO, IR, and Radio Continuum Emission from Ringed Galaxies
9.8 Kinematic Studies
10.Theories of Ring Formation
10.1 Some Historical Points
10.2 Fundamental Clues from Observations
11.Dynamics of Bars
11.1 Bar Formation
11.2 Orbits in a Barred Galaxy
11.3 Bars in Early-and Late-Type Galaxies
11.4 Pattern Speed Determination
11.5 Angular Momentum Transport
12.Gas Flows in Barred Galaxies
12.1 Hydrodynamics Modeling
12.2 Formation of Rings
12.3 Role of Viscosity
12.4 Fueling the Nucleus
13.Self-Gravitating Hydrodynamics
13.1 Stability
13.2 Self-Gravitating Rings and Nuclear Spirals
14.Problems with Ring Formation Theory
14.1 Time-scales and the Coexistence of Rings
14.2 Bar-Ring Misalignment
15.Rings in Nonbarred Galaxies
15.1 Bar Destruction, Lens, and Oval Formation
15.2 Evolution Along the Hubble Sequence
16.Interaction Between Several Waves
16.1 Nuclear Bars Inside Nuclear Rings
17.Tidal Interactions and Rings
17.1 The Leading Arm Ringed Galaxy NGC 4622
17.2 The One-Armed Outer-Ringed Galaxy NGC 4378
17.3 Accretion Rings
18.Single-Ringed, Multi-Armed Galaxies
19.Conclusions
References