  An analysis of the dynamics of a star formation event is performed. It is
shown that galaxies able to drive leftover gas to sufficient altitudes in a few
million years are characterized by two basic properties: small sizes (<1kpc)
and high star formation rate surface densities (Sigma_SFR > 10 Msun/yr/kpc2).
For the parameter space of relevance, the outflow is primarily driven by
supernovae with radiation pressure being significant but subdominant. Our
analysis provides the unifying physical origin for a diverse set of observed
LyC leakers, including the green-peas galaxies, [SII]-weak galaxies,
Lyman-alpha emitters, with these two characteristics as the common denominator.
Among verifiable physical properties of LyC leakers, we predict that (1) the
newly formed stellar masses are are typically in the range of 1e8-1e10 Msun,
except perhaps ULIRGs, (2) the outflow velocities are typically in the range
typically of 100-600km/s, but may exceed 1e3 km/s in ULIRGs, with a strong
positive correlation between the stellar masses formed and the outflow
velocities, (3) the overall escape fraction of galaxies is expected to increase
with increasing redshift, given the cosmological trend that galaxies become
denser and more compact with increasing redshift. In addition, two interesting
by-product predictions are also borne out. First, ULIRGs appear to be in a
parameter region where they should be prodigious LyC leakers, unless there is a
large ram-pressure. Second, Lyman break galaxies (LBGs) are not supposed to be
prodigious LyC leakers in our model, given their claimed effective radii
exceeding 1kpc.
