Galactic evolution and fragmentation bursts in the protohalo

The primordial eolution of the galactic halo is investigated, using a multifluid fragmenting-radiative eolution model. A new theory of fragmentation (1), supported by a suitable treatment of the radiative properties of the primordial halo gas (accounting also for the formation of molecular hydrogen and for its cooling effect) is used to predict the mass spectrum of the first stellar generation and to study the primordial fragmentation activity. The first stars form in the range (40,1000) solar masses, most likely in the protoglobular clusters. Strong fragmentation bursts appear after 200 Myr (about 1.2 galactic free-fall times)