FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS

We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps migrate into a bulge in < ∼10 dynamical times, or < ∼0.5 Gyr. The cosmological streams replenish the…