Lyman-Werner Escape Fractions from the First Galaxies
  Direct collapse black holes forming in pristine, atomically-cooling haloes at
$z \approx 10-20$ may act as the seeds of supermassive black holes (BH) at high
redshifts. In order to create a massive BH seed, the host halo needs to be
prevented from forming stars. H$_2$ therefore needs to be irradiated by a large
flux of Lyman-Werner (LW) UV photons in order to suppress H$_2$ cooling. A key
uncertainty in this scenario is the escape fraction of LW radiation from first
galaxies, the dominant source of UV photons at this epoch. To better constrain
this escape fraction, we have performed radiation-hydrodynamical simulations of
the growth of HII regions and their associated photodissociation regions in the
first galaxies using the ZEUS-MP code. We find that the LW escape fraction
crucially depends on the propagation of the ionisation front (I-front). For an
R-type I-front overrunning the halo, the LW escape fraction is always larger
than 95%. If the halo recombines later from the outside--in, due to a softened
and weakened spectrum, the LW escape fraction in the rest-frame of the halo
(the near-field) drops to zero. A detailed and careful analysis is required to
analyse slowly moving, D-type I-fronts, where the escape fraction depends on
the microphysics and can be as small as 3% in the near-field and 61% in the
far-field or as large as 100% in both the near-field and the far-field.
