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Astron. Astrophys. 347, 442-454 (1999)

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1. Introduction

The regular spiral arms observed in nearby disk galaxies are a manifestation of global spiral modes developed in galactic disks. Numerous linear and nonlinear studies have demonstrated that self-gravity plays a major role in the generation of global spiral modes (see, e.g. Binney and Tremaine 1987).

Growth of spirals on early stages of galactic evolution, however, occurs on a rapidly changing background. The precursors of present systems look bluer than old galaxies giving evidence for an enhanced star formation rate in early epochs. The colors and irregular structure seen in intermediate red-shifted galaxies suggest that they are a population of galaxies with massive star formation rapidly consuming gas in the galactic disks. These galaxies are the systems where star-formation might considerably change the physics of spiral dynamics.

In this paper we address the question how the evolution of the large-scale spiral perturbations is affected by the processes of mass and momentum exchange in a star forming disk. Kato (1972, 1974) discussed the effects of star-gas mass exchange in a linearly growing spiral mode. Using the WKB-approximation he found, that under some conditions the mass exchange between stars and gas can excite density waves. We extend this study by following the dynamics of the nonlinear hydrodynamical equations for three interacting components: the massive stars, the low mass stars (or stellar remnants) and the gas. We perform a series of 2D multi-phase hydrodynamical simulations of the dynamics of unstable multi-component disks, and compare our results with the morphological properties of spirals, growing in one-component self-gravitating disks. As a particular realization of the mass transformations in star-forming systems we choose the description of Köppen et al. (1995) which is a subset of the more detailed "chemo-dynamical" models developed by Theis et al. (1992), Hensler et al. (1993), Samland (1994) and Samland et al. (1997). Apart from previous papers investigating the interaction network of a multi-component system for spherical (Theis et al. 1992) or axisymmetric galaxies (Samland et al. 1997) we deal here with the evolution of thin, but non-axisymmetric systems. This allows us to study the influence of the interactions between the components on the evolution of spiral structure.

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© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999