Ubiquitous Molecular Outflows in z > 4 Massive, Dusty Galaxies II.
  Momentum-Driven Winds Powered by Star Formation in the Early Universe
  Galactic outflows of molecular gas are a common occurrence in galaxies and
may represent a mechanism by which galaxies self-regulate their growth,
redistributing gas that could otherwise have formed stars. We previously
presented the first survey of molecular outflows at z > 4 towards a sample of
massive, dusty galaxies. Here we characterize the physical properties of the
molecular outflows discovered in our survey. Using low-redshift outflows as a
training set, we find agreement at the factor-of-two level between several
outflow rate estimates. We find molecular outflow rates 150-800Msun/yr and
infer mass loading factors just below unity. Among the high-redshift sources,
the molecular mass loading factor shows no strong correlations with any other
measured quantity. The outflow energetics are consistent with expectations for
momentum-driven winds with star formation as the driving source, with no need
for energy-conserving phases. There is no evidence for AGN activity in our
sample, and while we cannot rule out deeply-buried AGN, their presence is not
required to explain the outflow energetics, in contrast to nearby obscured
galaxies with fast outflows. The fraction of the outflowing gas that will
escape into the circumgalactic medium (CGM), though highly uncertain, may be as
high as 50%. This nevertheless constitutes only a small fraction of the total
cool CGM mass based on a comparison to z~2-3 quasar absorption line studies,
but could represent >~10% of the CGM metal mass. Our survey offers the first
statistical characterization of molecular outflow properties in the very early
universe.
