What question did this study set out to answer?

The study aims to analyze the faint end of the luminosity function of galaxies at redshifts z ∼ 7-9.

February 24, 2026

A GLIMPSE into the very faint end of the Hbeta+O iii lambda lambda 4960; 5008 luminosity function at z ∼ 7 - 9 behind Abell S1063

Key Points

The study aims to analyze the faint end of the luminosity function of galaxies at redshifts z ∼ 7-9.
Utilized the GLIMPSE JWST/NIRCam survey for deep observations
Conducted spectral energy distribution fitting on 164 lensed galaxies
Measured combined flux to construct the emission line luminosity function
Explored several models to explain observed differences in luminosity functions
Converted luminosity function to calculate ionising photon-production rates.
Derived a faint-end slope of the luminosity function at α=-1.78 for z=8-9, which is flatter than the UV luminosity function
Galaxies with luminosities ≥ 10^39 contribute significantly to the ionising photon budget (31%-90% at z=7-8)
Found that very faint galaxies have a negligible effect on the total ionising photon-production rate
Consistent results with previous findings on cosmic star formation rate density.

Abstract

We used the ultra-deep GLIMPSE JWST/NIRCam survey to constrain the faint end of the ^ luminosity function (LF) down to 10³9 for z=7-8 and α=-1. 55_ at z ^ behind the lensed Hubble Frontier Field galaxy cluster Abell S1063. We applied a spectral energy distribution fitting on a Lyman-break galaxy selected sample of 164 lensed galaxies and measured their combined flux to build the emission line LF. We found a LF with a faint-end slope (α=-1. 78_ -0. 06 +0. 06 -0. 11 +0. 11 for z=8-9), which is flatter than the UV LF at similar redshifts (α łe -2) and suggests a lower number density of weak a decrease in the the effect of metallicity on the signs of a faint-end turnover in the UV LF. Under the assumption of an evolving ^ emitting galaxies at fixed We analysed several possible explanations: i) ratio due to bursty star formation histories (SFHs), ii) ratio, or iii) ratio, we separated the contribution of and and obtained a flatter LF (α=-1. 66_ -0. 05 +0. 05 for z=7-8 and α=-1. 45_ -0. 10 ^ +0. 09 for z=8-9) but steeper ^ LF (α=-1. 95_ -0. 08 +0. 08 for z=7-8 and α=-1. 68_ -0. 14 ^ +0. 13 for z=8-9). The combination of a decreasing metallicity and bursty SFH can reconcile the observed differences between the UV and _ LF. By converting this LF into the ionising photon-production rate dot N ̊m ion, we show that galaxies with L_ ≥ 10^ 39, that is, with a star formation rate (SFR) (_ 5 10^ -3 cause 31%-90% and 46%-156% of the ionising photon budget (at 7<z<8 and 8<z<9), when we assume a constant escape fraction of Lyman-continuum photon (fesc=0. 14). The shape of the LF further shows the negligible contribution of faint galaxies to the dot N ̊m ion. Additionally, we derived the cosmic star formation rate density (SFRD), finding results consistent with previous estimates. However, the sensitivity of GLIMPSE to lower SFRs reinforces the conclusion that very faint galaxies contribute very little to dot N _ ̊m ion and the SFRD. Our results suggests that GLIMPSE has detected the bulk of the total emission from star-forming galaxies, and that galaxies below our detection limits are likely minor contributors to cosmic re-ionisation.

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