Delayed star formation in high-redshift stream-fed galaxies
  We propose that star formation is delayed relative to the inflow rate in
rapidly-accreting galaxies at very high redshift (z > 2) because of the energy
conveyed by the accreting gas. Accreting gas streams provide fuel for star
formation, but they stir the disk and increase turbulence above the usual
levels compatible with gravitational instability, reducing the star formation
efficiency in the available gas. After the specific inflow rate has
sufficiently decreased - typically at z < 3 - galaxies settle in a
self-regulated regime with efficient star formation. An analytic model shows
that this interaction between infalling gas and young galaxies can
significantly delay star formation and maintain high gas fractions (>40%) down
to z = 2, in contrast to other galaxy formation models. Idealized hydrodynamic
simulations of infalling gas streams onto primordial galaxies confirm the
efficient energetic coupling at z > 2, and suggest that this effect is largely
under-resolved in existing cosmological simulations.
