Using four different suites of cosmological simulations , we generate synthetic spectra for galaxies with different Lyman continuum escape fractions ( f _ { \mathrm { esc } } ) at redshifts z \approx 7 –9 , in the rest-frame wavelength range relevant for the James Webb Space Telescope ( JWST ) NIRSpec instrument .
By investigating the effects of realistic star formation histories and metallicity distributions on the EW ( H \beta ) - \beta diagram ( previously proposed as a tool for identifying galaxies with very high f _ { \mathrm { esc } } ) , we find that neither of these effects are likely to jeopardize the identification of galaxies with extreme Lyman continuum leakage .
Based on our models , we expect that essentially all z \approx 7 –9 galaxies that exhibit rest-frame EW ( H \beta ) \lesssim 30 Å to have f _ { \mathrm { esc } } > 0.5 .
Incorrect assumptions concerning the ionizing fluxes of stellar populations or the dust properties of z > 6 galaxies can in principle bias the selection , but substantial model deficiencies of this type should at the same time be evident from offsets in the observed distribution of z > 6 galaxies in the EW ( H \beta ) - \beta diagram compared to the simulated one .
Such offsets would thereby allow JWST/NIRSpec measurements of these observables to serve as input for further model refinement .