6. Discussion and conclusion
We have shown that, in simulations without energy input, the evolution of the fractal dimension depends on the initial conditions and also, to some extent, on the dissipation schemes. Then we have investigated the effects of an energy input on the dynamics of the system. This input is necessary to prevent the total collapse of the system. Moreover, we do not want the input to destroy the inhomogeneous fractal structure of the medium, as done by random reinjections (thermal bath, random force field). Among the solutions we have tested, only the highly regular force field provided by the galactic shear preserves an inhomogeneous state. However this state is quite strongly constrained by the geometry of the shear. Stripes appear as a result. Interestingly, clumps are formed in these stripes and can be destroyed if we have an efficient enough density cutoff.
This state does not have a well-defined fractal dimension. Stripes are the effect of a large scale action on the system and within our dynamic range in scale, we cannot get rid of this boundary effect. If we had more resolution, the clumps could fragment, and we might reach a scale domain free of boundary effects. One of our prospects is to follow the inner dynamic of a clump with simulations in recursive sub-boxes going down in scale. This can produce a great dynamic scale range but only in a small region of space.
© European Southern Observatory (ESO) 2000
Online publication: August 23, 2000