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Astron. Astrophys. 360, 76-84 (2000) 7. Discussion and conclusionsIn this paper we have investigated the coupling between DM and baryons during an assumed monolithic formation of two galaxies: a giant and a dwarf spheroidal galaxy. Starting from a homogeneous distribution, baryons sink toward the
center of the virialized DM halo due to cooling instability. The
smallest object has about 10 independent episodes of star formation
A crucial and sensitive aspect of our simulations is that both the
giant and the dwarf object have been modeled with the same number of
particles, which implies an increase by a factor
To check whether the results for the SF histories depend on the mass resolution of our simulations, the giant galaxy has been re-simulated using 2,000, 20,000 and 200,000 particles, whilst the dwarf galaxy has been re-simulated using 2,000 and 20,000 particles. This way the mass resolution goes from
In both cases we show a reasonable convergence of the results. As for the giant galaxy (see Fig. 2), we show that the SF history is dominated by a single ancient burst of SF, whose trend does not change too much passing from 2,000 to 200,000 particles. Nevertheless, a more careful analysis shows that a difference emerges passing from 2,000 to 20,000 particles, whereas passing from 20,000 to 200,000 particles does not significantly change the global result. Although the SF peak is almost the same in all the simulations, the
low resolution run produces a burst larger than the other two cases.
Correspondingly, the amount of gas consumed (and hence the final mass
in stars) passes from These conclusions confirm previous analyses on the performances of the SPH method (Steinmetz & Müller 1993, Thacker et al. 1998). By comparing different SPH implementations they find that the minimum number of particles required to calculate local physical variables in dynamically evolving systems is about 10,000, and that the SPH method can give reasonable results also by using a small number of particles. On the other hand, changing the resolution by a factor of 10 does not alter the SF history of the dwarf galaxy (see Fig. 7), which exhibits several episodes of SF, although the number and position of the peaks does not coincide exactly. The basic results of this paper can be summarized as follows:
In forthcoming papers we are going to analyze simulations which adopt different initial conditions for DM, in order to test the effect of the DM initial properties (density profile, velocity dispersion and so forth) on the final baryon distribution. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 2000 Online publication: July 27, 2000 ![]() |