Issue |
Astron. Astrophys. Suppl. Ser.
Volume 119, Number 2, October II 1996
|
|
---|---|---|
Page(s) | 231 - 248 | |
DOI | https://doi.org/10.1051/aas:1996241 | |
Published online | 15 October 1996 |
Cellular Automaton experiments on local galactic structure. I. Model assumptions
1
Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK, and Institut d'Astrophysique, 5, Avenue de Cointe, B–4000 Liège, BelgiumPermanent address
2
Institut de Physique, Sart–Tilman, B–4000, Liège, Belgium
Send offprint request to: J. Perdang
Received:
27
October
1994
Accepted:
6
March
1996
The purpose of the present paper, combined with the companion
paper (Lejeune & Perdang 1995, hereinafter Paper II), is to
demonstrate that a Cellular Automaton (CA) framework
incorporating detailed physical evolutionary mechanisms of the
galactic components provides a straightforward approach for
simulating local structural features in galaxies (such as those
of flocculent spiral galaxies). Conversely, and more important,
the observed local irregularities may give information on the
relevant timescales of the evolutionary processes operating in
these galaxies.
In this paper we start out with a critical review of the more
standard methods in use in galactic modelling. We insist on the
fact that these models do not lend themselves to a
straightforward inclusion of both the galactic dynamics and the
physical evolution of the galactic components. We show that the
Cellular Automaton approach can combine both effects, on
condition that the dynamics is approximated by a stationary, in
general space–dependent velocity field of the galactic matter.
The main part of the paper addresses an extension of the
Stochastic Propagating Star Formation scheme originally devised
by Mueller & Arnett (1976). The model consists in a
multi–state CA specifically designed to deal with the
evolutionary behaviour of an off-centre region of a galaxy, of
an area of a few
. The model incorporates a
detailed sequence of in part parametrised stellar evolutionary
processes. In the version discussed here it includes as
dynamical effects the motions of galactic matter due to a
stationary circulation and, to some extent, due to the proper
motions of the stars.
The model we present is a first nontrivial instance of a CA
defined over a lattice lacking geometric symmetries (crystal
symmetries of standard CA, or rotational symmetry of the
Mueller–Arnett CA). The precise geometry of the CA network of
cells is imposed in our model by the space–dependent stationary
galactic velocity field. Numerical results are discussed in the
companion paper.
Key words: galaxies: structure / star formation / methods: numerical
© European Southern Observatory (ESO), 1996