Project Lyman: Quantifying 11 Gyrs of Metagalactic Ionizing Background
  Evolution
  The timing and duration of the reionization epoch is crucial to the emergence
and evolution of structure in the universe. The relative roles that
star-forming galaxies, active galactic nuclei and quasars play in contributing
to the metagalactic ionizing background across cosmic time remains uncertain.
Deep quasar counts provide insights into their role, but the potentially
crucial contribution from star-formation is highly uncertain due to our poor
understanding of the processes that allow ionizing radiation to escape into the
intergalactic medium (IGM). The fraction of ionizing photons that escape from
star-forming galaxies is a fundamental free parameter used in models to
"fine-tune" the timing and duration of the reionization epoch that occurred
somewhere between 13.4 and 12.7 Gyrs ago (redshifts between 12 > z > 6).
However, direct observation of Lyman continuum (LyC) photons emitted below the
rest frame \ion{H}{1} ionization edge at 912 \AA\ is increasingly improbable at
redshifts z > 3, due to the steady increase of intervening Lyman limit systems
towards high z. Thus UV and U-band optical bandpasses provide the only hope for
direct, up close and in depth, observations of the types of environment that
favor LyC escape. By quantifying the evolution over the past 11 billion years
(z < 3) of the relationships between LyC escape and local and global parameters
..., we can provide definitive information on the LyC escape fraction that is
so crucial to answering the question of, how did the universe come to be
ionized? Here we provide estimates of the ionizing continuum flux emitted by
"characteristic" (L_{uv}^*) star-forming galaxies as a function of look back
time and escape fraction, finding that at z = 1 (7.6 Gyrs ago) L_{uv}^*
galaxies with an escape fraction of 1% have a flux of 10^{-19} ergs cm^{-2}
s^{-1} \AA^{-1}.
