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We explore the qualitative changes that would occur if the amplitude Q ∼ 10 −5 of cosmological density fluctuations were different. If Q ∼ < 10 −6 , the cosmological objects that form would have so low virial temperatures that they may be unable to cool and form stars, and would be so loosely bound that even if they could produce a supernova explosion, they(More)
We study the expected distribution of massive black hole (MBH) spins and its evolution with cosmic time in the context of hierarchical galaxy formation theories. Our model uses Monte Carlo realizations of the merger hierarchy in a ΛCDM cosmology, coupled to semi-analytical recipes, to follow the merger history of dark matter halos, the dynamics of the MBHs(More)
We describe a mechanism by which supermassive black holes can form directly in the nuclei of protogalaxies, without the need for " seed " black holes left over from early star formation. Self-gravitating gas in dark matter halos can lose angular momentum rapidly via runaway, global dynamical instabilities, the so-called " bars within bars " mechanism. This(More)
We investigate the ability of primordial gas clouds to retain molecular hydrogen (H 2) during the initial phase of the reionization epoch. We nd that before the Strr omgren spheres of the individual ionizing sources overlap, the UV background below the ionization threshold is able to penetrate large clouds and suppress their H 2 abundance. The consequent(More)