The mean Hα EW and Lyman- continuum photon production efficiency for faint z ≈ 4-5 galaxies

We present the first measurements of the Lyman-continuum photon production efficiency xi(ion.0) at z similar to 4-5 for galaxies fainter than 0.2 L* (-19 mag). xi(ion.0) quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of xi(ion.0) to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe xi(ion.0) to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and approximate to 300 3 < z < 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6] [4.5] colors are derived and used to infer the H alpha rest-frame equivalent widths, which range from 403 angstrom to 2818 angstrom. The derived xi(ion.0) is log(10)(xi(ion.0)/Hz erg(-1)) = 25.36 0.08 over-20.5 < Muv <-17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that 6011 shows no strong dependence on M-UV. The xi(ion.0) values found in our sample imply that the Lyman-continuum escape fraction for M-UV approximate to-19 star-forming galaxies cannot exceed approximate to 8-20% in the reionization era.