Steady Outflows in Giant Clumps of High-z Disk Galaxies During Migration
  and Growth by Accretion
  We predict the evolution of giant clumps undergoing star-driven outflows in
high-z gravitationally unstable disk galaxies. We find that the mass loss is
expected to occur through a steady wind over many tens of free-fall times (t_ff
~ 10 Myr) rather than by an explosive disruption in one or a few t_ff. Our
analysis is based on the finding from simulations that radiation trapping is
negligible because it destabilizes the wind (Krumholz & Thompson 2012, 2013).
Each photon can therefore contribute to the wind momentum only once, so the
radiative force is limited to L/c. When combining radiation, protostellar and
main-sequence winds, and supernovae, we estimate the total direct injection
rate of momentum into the outflow to be 2.5 L/c. The adiabatic phase of
supernovae and main-sequence winds can double this rate. The resulting outflow
mass-loading factor is of order unity, and if the clumps were to deplete their
gas the timescale would have been a few disk orbital times, to end with half
the original clump mass in stars. However, the clump migration time to the disk
center is on the order of an orbital time, about 250 Myr, so the clumps are
expected to complete their migration prior to depletion. Furthermore, the
clumps are expected to double their mass in a disk orbital time by accretion
from the disk and clump-clump mergers, so their mass actually grows in time and
with decreasing radius. From the 6-7 giant clumps with observed outflows, 5 are
consistent with these predictions, and one has a much higher mass-loading
factor and momentum injection rate. The latter either indicates that the
estimated outflow is an overestimate (within the 1-sigma error), that the SFR
has dropped since the time when the outflow was launched, or that the driving
mechanism is different, e.g. supernova feedback in a cavity generated by the
other feedbacks.
