High-z Galaxy Formation in the Standard Cosmology

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.