Physics
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280...85t&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 1, p. 85-104
Physics
26
Astronomical Models, Cloud Physics, Computerized Simulation, Dissipation, Galactic Evolution, Galactic Structure, Interstellar Matter, Mathematical Models, Molecular Clouds, Hydrodynamic Equations, Hydrodynamics, Many Body Problem, Protostars, Star Formation
Scientific paper
We present numerical simulations of dissipative cloud systems. The orbits of single clouds are followed including fully inelastic collisions. A comparison between N-body simulations and the standard statistical approach of cloud-cloud collisions used in hydrodynamical models shows a good agreement during the early non-linear evolution. However, after a few crossing timescales large differences arise due to the orbit-dependent collisional probability: In the N-body simulation the collapse induced by dissipation achieves a quasi-equilibrium state whereas in the hydrodynamical model the collapse continues. Due to non-linear effects the dissipational timescale is reduced by a factor of 5 compared to the standard estimate. Hence dissipation is able to induce a violent collapse even if the system is initially near virial equilibrium. In order to simulate protogalactic systems the clouds are modelled according to observations in the Galaxy. Star formation is included crudely by an upper mass limit for the coalescence of clouds. A model for a non-rotating cloud system of 1011 solar mass shows a violent collapse even in the case of a large initial virial coefficient of 0.5. In an initially fast-rotating cloud system the clouds without any inelastic collisions build up a flattened ellipsoid (with a 2:1 axis ratio). The highly dissipative component, however, forms a thin disk of 1.5 kpc scale height and a central spheroid with an effective radius of about 1 kpc. The disk shows an exponential profile with a scale radius of 5 kpc. The dissipation by cloud-cloud collisions creates not only a disk but is also able to feed a galactic bulge since the inelastic collisions lead to more radial orbits passing the central region.
Hensler Gerhard
Theis Ch
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