  We present the calculations of steady, spherical gas outflows from galaxies
in an effort to understand the effects of the galaxy mass on the flow
properties such as the size of the outflow regions, the efficiency of radiative
cooling, and the fate of the cooled gas. We show that there exist no transonic
flows but either subsonic or supersonic flows are obtainable, in an analogy
with the stellar wind or accretion problems. Solutions of the supersonic
outflows are studied in detail as they are most likely to carry gas to large
distances away from galaxies. In case the gas does cool radiatively, the cooled
gas is most likely to form clouds via various instabilities. The clouds coast
farther away from the galaxy because of the finite kinetic energy they inherit.
Depending on the initial energies, the clouds can either leave the galaxy or
fall back ballistically. Applications of the calculations to dwarf and normal
galaxies are made, and we argue that normal galaxies like our own should have
relatively small gaseous halos formed through this mechanism. We discuss the
implications of cold clouds from dwarf galaxies on recent observations of the
QSO absorption line systems. For massive galaxies, satellites provide
alternative ways to form large gaseous halos. We show how dynamical friction
can increase tidal stripping of the gas as the satellite spirals in toward the
primary, and that the gas ejected from satellites may account for the QSO heavy
element absorption lines.
