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Astron. Astrophys. 334, 29-38 (1998)


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Formation of disk galaxies

I. From a hot gaseous envelope

V. Missoulis 1, 2

1 Sternberg Astronomical Institute, Moscow State University
2 Astronomical Institute, National Observatory of Athens, P.O. Box 20048, GR-118 10 Athens, Greece

Received 16 December 1996 / Accepted 1 December 1997

Abstract

The problem of the formation of a disk galaxy from a spherical, rotating, hot, gaseous envelope is solved by the means of a 2-D hydrodynamic code. Thermal instability and formation of clouds, cloud evaporation due to the hot surroundings and ram pressure, dynamical interaction between the gas and the clouds, energy dissipation by cloud-cloud collisions and radiation cooling of the intercloud gas are taken into account. Thermal conductivity is ignored. The most important of the results obtained are as follows:

  1. At the time of the formation of the disk, the phase transitions lead to angular momentum transfer from the outer to the inner regions. If the temperature initially is independent of the distance from the center, the most important factor of the angular momentum transfer is the evaporation of the clouds. If initially the temperature is smaller at the outer regions, the most important factor of the angular momentum transfer is cloud-cloud collisions.
  2. The observed exponential profiles can be understood as the result of angular momentum transfer due to the viscosity, which becomes important after the violent stage of the formation of the gaseous disk.
  3. The model can explain the origin of the HI clouds located at large distances from the axis of spiral galaxies.

Owing to the complicated mathematics, the gas-cloud dynamical interactions and the numerical method are presented only in the on-line version of the paper.

Key words: hydrodynamics – galaxies: formation – galaxies: spiral

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998

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