Lyman continuum leakage versus quenching with the James Webb Space
  Telescope: The spectral signatures of quenched star formation activity in
  reionization-epoch galaxies
  In this paper, we study the effects of a recent drop in star formation rate
(SFR) on the spectra of epoch of reionization (EoR) galaxies, and the resulting
degeneracy with the spectral features produced by extreme Lyman continuum
leakage. In order to study these effects in the wavelength range relevant for
the upcoming James Webb Space Telescope (JWST), we utilize synthetic spectra of
simulated EoR galaxies from cosmological simulations together with synthetic
spectra of partially quenched mock galaxies. We find that rapid declines in the
SFR of EoR galaxies could seriously affect the applicability of methods that
utilize the equivalent width of Balmer lines and the ultraviolet spectral slope
to assess the escape fraction of EoR galaxies. In order to determine if the
aforementioned degeneracy can be avoided by using the overall shape of the
spectrum, we generate mock NIRCam observations and utilize a classification
algorithm to identify galaxies that have undergone quenching. We find that
while there are problematic cases, JWST/NIRCam or NIRSpec should be able to
reliably identify galaxies with redshifts $z\sim 7$ that have experienced a
significant decrease in the SFR (by a factor 10-100) in the past 50-100 Myr
with a success rate $\gtrsim 85\%$. We also find that uncertainties in the
dust-reddening effects on EoR galaxies significantly affect the performance of
the results of the classification algorithm. We argue that studies that aim to
characterize the dust extinction law most representative in the EoR would be
extremely useful.
