  The first sources of ionizing radiation to condense out of the dark and
neutral IGM sent ionization fronts sweeping outward through their surroundings,
overtaking other condensed objects and photoevaporating them. This feedback
effect of universal reionization on cosmic structure formation is demonstrated
here for the case of a cosmological minihalo of dark matter and baryons exposed
to an external source of ionizing radiation with a quasar-like spectrum, just
after the passage of the global ionization front created by the source. We
model the pre-ionization minihalo as a truncated, nonsingular isothermal sphere
in hydrostatic equilibrium following its collapse out of the expanding
background universe and virialization. Results are presented of the first gas
dynamical simulations of this process, including radiative transfer. A sample
of observational diagnostics is also presented, including the spatially-varying
ionization levels of C, N, and O in the flow if a trace of heavy elements is
present and the integrated column densities of H I, He I and II, and C IV thru
the photoevaporating gas at different velocities which would be measured in
absorption against a background source like that responsible for the
ionization.
