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Astron. Astrophys. 360, 76-84 (2000)

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4. Initial configuration

We set up a protogalaxy as an isolated virialized DM halo with baryonic material inside it. We assume spherical, isotropic and non-rotating halos of density profiles:


Notethat Eq. (2) matches the profile of CDM halos in the innermost regions, especially in low [FORMULA] Universe for which [FORMULA] kpc. Different profiles, more in line with observations or theoretical claims, will be considered in forthcoming papers.

Gravitational interaction is modeled by adopting a Plummer softening constant over the simulation and is equal for both DM and gas. By plotting the inter-particles separation as a function of the galactocentric distance, we derive the softening parameter [FORMULA] as the mean inter-particles separation at the center of the sphere, taking at least one hundred particles inside the softening radius.

DM particles (10,000 in number) are distributed inside a sphere according to an acceptance-rejection procedure for generating random deviations with a known distribution function (Press et al. 1989).

Along with positions, we also assign the isotropic dispersion velocity [FORMULA] according to:


which is the solution of the Jeans equation for spherical isotropic collisionless system with the density profile of Eq. (2).

Fixing the total mass of the system [FORMULA], we assume that a radius


truncates the dark halo, where [FORMULA] is the critical density to close the Universe.


Table 1. Properties of the virialised primordial DM halos.

The systems are then allowed to evolve until virial equilibrium is reached. 10,000 baryonic particles are then homogeneously distributed inside the DM halo with zero velocity field and low metal content ([FORMULA]). The initial gas temperature is [FORMULA] oK.

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© European Southern Observatory (ESO) 2000

Online publication: July 27, 2000