A GLIMPSE into the very faint-end of the Hβ+OIIIλλ4960, 5008 luminosity function at z=7-9 behind Abell S1063

We use the ultra-deep GLIMPSE JWST/NIRCam survey to constrain the faint-end of the Hβ+OIIIλλ4960, 5008 luminosity function (LF) down to 10^39 erg/s at z=7-9 behind the lensed Hubble Frontier Field Abell S1063. We perform SED fitting on a Lyman-Break Galaxy sample, measuring combined Hβ+OIII fluxes to construct the emission-line LF. The resulting LF (α=-1. 55 to -1. 78) is flatter than the UV LF (α10^39 erg/s (SFR (Hα) >510^-3 M_/yr) contribute 21-61% and 24-104% of the ionising photon budget at 7<z<8 and 8<z<9, respectively (for f₄ₒ₂=0. 1). The LF shape suggests faint galaxies contribute minimally to the ionising photon production rate. Our cosmic star formation rate density (CSFRD) estimates align with previous work, but GLIMPSE's sensitivity to low SFRs confirms that very faint galaxies are minor contributors to both the ionising photon production rate and the CSFRD. Our results suggest that GLIMPSE has detected the bulk of the total Hβ+OIII emission from star-forming galaxies, with fainter sources playing a limited role in cosmic reionisation.