The Implications of Extreme Outflows from Extreme Starbursts
  Interstellar ultraviolet absorption-lines provide crucial information about
the properties of galactic outflows. In this paper, we augment our previous
analysis of the systematic properties of starburst-driven galactic outflows by
expanding our sample to include a rare population of starbursts with
exceptionally high outflow velocities. In principle, these could be a
qualitatively different phenomenon from more typical outflows. However, we find
that instead these starbursts lie on, or along the extrapolation of, the trends
defined by the more typical systems studied previously by us. We exploit the
wide dynamic range provided by this new sample to determine scaling relations
of outflow velocity with galaxy stellar mass (M*), circular velocity,
star-formation rate (SFR), SFR/M*, and SFR/area. We argue that these results
can be accommodated within the general interpretational framework we previously
advocated, in which a population of ambient interstellar or circum-galactic
clouds is accelerated by the combined forces of gravity and the momentum flux
from the starburst. We show that this simple physical picture is consistent
with both the strong cosmological evolution of galactic outflows in typical
star-forming galaxies and the paucity of such galaxies with spectra showing
inflows. We also present simple parameterizations of these results that can be
implemented in theoretical models and numerical simulations of galaxy
evolution.
