8 April 2010

Speaker: Avishai Dekel (Hebrew University)

Title:High-z Galaxy Formation in the Standard Cosmology

Abstract:Using hydro-cosmological simulations and analytic modeling, we attempt solid predictions for the formation of massive galaxies at high redshift within the LCDM cosmology. The emerging new picture highlights the formation of galaxies at the nodes of the cosmic web. These galaxies are steadily fed by cold streams along dark-matter filaments, which are observable in Lyman-alpha. The streams, including a smooth component and merging galaxies, penetrate through hot gas in dark-matter halos to form extended, turbulent, rotating disks and bulges. The intense gas input drives a self-regulated, violent gravitational disk instability with transient features and giant clumps, where stars form rapidly. The violent instability induces quick migration to the center, complementing mergers as a mechanism for spheroid formation. The clumpy disks evolve in steady state for a few Gyr, where star formation and bulge growth are governed by the cosmological streaming. Star formation is suppressed in small halos by stellar feedbacks and in massive halos by gravitational quenching and AGN feedback --- these processes pose interesting open questions. We propose that the development of disks versus spheroids, and the opposite phenomena of star formation and quenching, are all determined by the streams' intensity and degree of clumpiness. The role of major mergers in star formation and quenching is secondary. This picture seems consistent with recent observations of galaxies at high redshifts.

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