Spiral structure in galaxies: a density wave theory

Abstract

Introduction - morphology and semiempirical approach co-existence of small- and large-scale structures excitation of spiral structure three persistence problems and main-tenance of spiral structure roles of the cold, dissipative gas component the dynamical window prevalence of two-armed grand designs barred spirals scales of motion viability of the model approach for normal spirals a physical per-spective future developments. Part 1 Physical concepts: physical and morphological characteristics of galaxies - hubble classification, overall characteristics of spiral galaxies, morphology of spiral arms, major issues addressed in this monograph, relation to other astrophysical themes of general interest the concept of density waves - density waves versus material arms, tendency for the formation of spiral waves, collective behaviour, a preliminary formulation of the hypothesis of quasi-stationary spiral structure density waves, interstellar medium, and star formation - processes of star formation, sketch of the large-scale shock scenario, direct simple evidence of density waves, mechanisms of self-regulation regularity, morphological classification, and the concept of spiral modes - global modes as intrinsic characteristics of the galaxy, excitation mechanisms, linearly growing modes, moderately growing modes, nonlinear equilibration, the hypothesis of quasi-stationary spiral structure, morphology of modes - normal spirals versus barred spirals, grand design versus flocculent galaxies, a tentative interpretation of the hubble sequence, tides and well-developed bars. Part 2 Observational studies: external galaxies - in search of a unifying framework for ob-servations, morphology, luminosity classification and star formation, kinematics, modeling the milky way - a unique case, spiral arms and spiral features, kinematics, modeling the solar neighbourhood. Part 3 Dynamical mechanisms: basic models and relevant parameter regimes - modeling of the basic state, zero-thickness dynamical models, kinematics of a differentially rotating disk geometry of wave patterns - density maxima, potential minima, and number of arms, pattern frequency, pitch angle of spiral structure, trailing and leading, normal spiral structure, barred spiral structure, and oval distortions, trapping of orbits at resonances and self-consistency. (Part contents).