The most prominent processes of star formation in galactic disks with
redshifts up to z~5 can be observed directly with the HST ACS. Star
formation is in the form of giant clumps, containing 10^8 to 10^9
Msun, which have an exponential distribution with galactocentric
radius. Computer simulations show the evolution of these clumps. Star
formation in interacting galaxies out to z~1.5 looks pretty
normal, although the clumps are again unusually massive. Most galaxies are
smaller beyond z~1, including antenna-shaped interactions. So far, star
formation appears to involve primarily gravitational instabilities in
highly turbulent, high-column-density gas disks. Monolithic collapse
(i.e., star formation in spheroids) does not appear relevant; evidence for
early formation of ellipticals should be interpreted instead as rapid
assembly of disks and smaller ellipticals in very dense environments. There
is no evidence so far for triggered star formation in shells, or for
blowout or feedback associated with star formation in z~2 to 5
disks. Between z~2 and z~5, star formation also occurs in compact galaxies
or submm galaxies, which are usually not resolved well, so the processes
involved are not yet known.
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