SPICA as a probe of cosmic reionization
  Current data indicate that the reionization of the Universe was complete by
redshift z~6-7, and while the sources responsible for this process have yet to
be identified, star-forming galaxies are often considered the most likely
candidates. However, the contribution from z>6 galaxies to cosmic reionization
critically depends on the fraction of ionizing (Lyman continuum, LyC) photons
escaping from these objects and into the intergalactic medium. At z<4, the
escaping LyC flux can be measured directly, but the opacity of the neutral
intergalactic medium precludes such measurements at higher redshifts. In a
recent paper, we argue that since the LyC escape fraction regulates the
contribution of nebular emission to the rest-frame optical/UV spectra of
galaxies, the James Webb Space Telescope should be able to indirectly assess
the LyC escape fraction for galaxies at z~6-9. JWST can, on the other hand, not
constrain the fraction of LyC photons directly absorbed by dust, and this is
where SPICA comes in. The dust continuum emission from gravitationally lensed
LyC-leakers at z=6 may in principle be detectable with SPICA, thereby
constraining the level of LyC extinction in these objects.
