The formation of globular clusters and dark clusters

The Fall-Rees theory of globular cluster formation assumes that thermal instability in the collapsing gas of a protogalaxy gives rise to cool clouds embedded in a hot medium. These clouds, which have temperatures close to 104 K and Jeans masses around 106 solar masses, are identified as the precursors of globular clusters. In the present work we suggest that molecular hydrogen cools the clouds to temperatures around 102 K corresponding to Jeans masses of about 102 solar masses. We further argue that these clouds form clusters of brown dwarfs, so that dark galactic haloes may be baryonic. The most massive clouds fragment into visible stars including globular clusters. These two modes of star formation may be a consequence of a pressure-dependent stellar initial mass function, as has been suggested in the context of cluster cooling flows, although other interpretations are also discussed. (author)