Identifying reionization-epoch galaxies with extreme levels of Lyman
  continuum leakage in James Webb Space Telescope surveys
  The James Webb Space Telescope (JWST) NIRSpec instrument will allow
rest-frame ultraviolet/optical spectroscopy of galaxies in the epoch of
reionization (EoR). Some galaxies may exhibit significant leakage of
hydrogen-ionizing photons into the intergalactic medium, resulting in faint
nebular emission lines. We present a machine learning framework for identifying
cases of very high hydrogen-ionizing photon escape from galaxies based on the
data quality expected from potential NIRSpec observations of EoR galaxies in
lensed fields. We train our algorithm on mock samples of JWST/NIRSpec data for
galaxies at redshifts $z=6$--10. To make the samples more realistic, we combine
synthetic galaxy spectra based on cosmological galaxy simulations with
observational noise relevant for $z\gtrsim 6$ objects of a brightness similar
to EoR galaxy candidates uncovered in Frontier Fields observations of galaxy
cluster Abell-2744 and MACS-J0416. We find that ionizing escape fractions
($f_\mathrm{esc}$) of galaxies brighter than $m_\mathrm{AB,1500} \approx 27$
mag may be retrieved with mean absolute error $\Delta
f_\mathrm{esc}\approx$0.09(0.12) for 24h (1.5h) JWST/NIRSpec exposures at
resolution R=100. For 24h exposure time, even fainter galaxies
($m_\mathrm{AB,1500} < 28.5$ mag) can be processed with $\Delta
f_\mathrm{esc}\approx$0.14. This framework simultaneously estimates the
redshift of these galaxies with a relative error less than 0.03 for both 24h
($m_\mathrm{AB,1500} < 28.5$ mag) and 1.5h ($m_\mathrm{AB,1500} < 27$ mag)
exposure times. We also consider scenarios where just a minor fraction of
galaxies attain high $f_\mathrm{esc}$ and present the conditions required for
detecting a subpopulation of high $f_\mathrm{esc}$ galaxies within the dataset.
