CANUCS: UV and ionizing properties of dwarf star-forming galaxies at z ∼ 5-7

The epoch of reionization (EoR) progressed through the emission of ionizing photons from galaxies to their local intergalactic medium. In this work, we characterize the dwarf star-forming galaxies as candidates for the source of ionizing photons that drove EoR. We investigate the ionizing properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at 4.8 < z < 7 using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass (2 x 10(6) <= M-*/M-circle dot <= 5 x 10(9)) and ultraviolet (UV) magnitudes (-22.68 <= M-UV <= = -15.95). We find a median UV slope beta(1500) of -2.56 +/- 0.23 and the production efficiency of ionizing photons log(xi ion) = 25.39 +/- 0.6 for the full sample (4.8 < z < 7) with a median stellar mass of 6.3 +/- 0.5 x 10(7) M-circle dot. We find both beta(1500) and xi(ion) are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionization of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in xi(ion) and a large scatter in H alpha equivalent widths (EWs). Finally, we investigate the trends of H alpha and [O III] + H beta EWs with UV magnitude and find M-UV is correlated between H alpha but not with [O III] + H beta EWs indicating low metallicities and recent burst in the UV faint galaxies.