| Abstract : | There are two main types of galaxy formation models. The first asserts that massive elliptical galaxies formed in a single, rapid collapse of gas and dark matter, during which virtually all the gas was turned quickly into stars. Afterward the galaxies changed only slowly as the stars evolved. This is what astronomers call a “top-down” scenario. The second model suggests that today’s giant ellipticals were formed mostly through mergers of smaller galaxies that had already converted at least some of their gas into stars—a “bottom-up” scenario. Here we show the possibility of such formation of galaxies in the early universe.
The cloud of DM collapses under gravity as there is no radiation pressure to oppose it which gives the critical radius as R≈10^21 cm. This radius will give the Mass of the collapsing DM cloud to form a SMBH of ≈10^42 g≈10^9 M_⨀. The free fall time, is found to be 10^8 years. Thus 10^9 M_⨀ DM blackholes could form at Z=100, on a timescale of 10^8 years. The Baryonic matter after decoupling collapses on this primordial DM structure which heats up the baryonic matter which then cools emitting bremsstrahlung. Considering the free fall time to be greater than the cooling time, the mass of Baryonic cloud is found to be around 10^12 M_⊙ with a radius of 50kpc. Thus we have a central BH of DM of mass ∼10^9 M_⊙ surrounded by baryonic matter of ∼10^11- 10^12 M_⊙ extending up to several kpc. In this scenario, even large galaxies can form early. As these cloud collapses, it can fragment into stars. The DM clouds can also fragment while collapsing forming DM planets and other compact objects. This scenario also explains the presence of SMBHs observed recently at high redshifts.
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