Theoretical considerations for star formation at low and high redshift
  Star formation in strongly self-gravitating cloud cores should be similar at
all redshifts, forming single or multiple stars with a range of masses
determined by local magneto-hydrodynamics and gravity. The formation processes
for these cores, however, as well as their structures, temperatures, Mach
numbers, etc., and the boundedness and mass distribution functions of the
resulting stars, should depend on environment, as should the characteristic
mass, density, and column density at which cloud self-gravity dominates other
forces. Because the environments for high and low redshift star formation
differ significantly, we expect the resulting gas to stellar conversion details
to differ also. At high redshift, the universe is denser and more gas-rich, so
the active parts of galaxies are denser and more gas rich too, leading to
slightly shorter gas consumption timescales, higher cloud pressures, and
denser, more massive, bound stellar clusters at the high mass end. With shorter
consumption times corresponding to higher relative cosmic accretion rates, and
with the resulting higher star formation rates and their higher feedback
powers, the ISM has greater turbulent speeds relative to the rotation speeds,
thicker gas disks, and larger cloud and star complex sizes at the
characteristic Jeans length. The result is a more chaotic appearance at high
redshift, bridging the morphology gap between today's quiescent spirals and
today's major-mergers, with neither spiral nor major-merger processes actually
in play at that time. The result is also a thick disk at early times, and after
in-plane accretion from relatively large clump torques, a classical bulge.
Today's disks are thinner, and torque-driven accretion is slower outside of
inner barred regions. This paper reviews the basic processes involved with star
formation in order to illustrate its evolution over time and environment.
