A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models
Year: 2026
Type: article
Abstract: We present a comprehensive study of the galaxy UV luminosity function (UVLF) at z = 6 − 9 leveraging deep JWST observations from the GLIMPSE survey. Thanks to gravitational lensing, we probe the UVLF to an unprecedented depth of M UV = − 12 mag, approximately three magnitudes deeper than previous robust constraints. Our UVLF determination incorporates a rigorous end-to-end uncertainty framework, including statistical and systematic lensing uncertainties. We find that the z ∼ 7 UVLF continues to rise steeply with a faint-end slope of α = − 1.98 − 0.05 + 0.06 . Crucially, our data show no clear evidence of a turnover down to = − 12.3 . The persistence of this faint population provides stringent constraints on galaxy formation models and cosmological simulations that predict an early flattening of the luminosity function due to radiative feedback or star-formation thresholds. Furthermore, post-JWST models specifically calibrated to match the UV-bright excess at z > 10 generally fail to reproduce the observed evolution toward lower redshifts and fainter magnitudes, highlighting a significant tension in our current understanding of early galaxy assembly. We derive a comoving ionizing emissivity at z = 7 of log( n i o n / s Mpc) ≈ 50.85 , which suggests that faint galaxies dominate the ionizing budget, providing enough photons to maintain reionization even in a highly clumped IGM ( C HII = 5 ). As our detection of faint galaxies effectively rules out a luminosity function truncation at M UV ≥ − 15 , these results emphasize the need to either accurately characterize the ionizing properties of the global, low-mass galaxy population at z > 6 , or to refine physical models of intergalactic medium clumping and its redshift evolution to maintain consistency with the observed reionization timeline.
Source: The Open Journal of Astrophysics
DOI: 10.33232/001c.166816
Authors: Hakim Atek, Iryna Chemerynska, Lukas J. Furtak, Johan Richard, John Chisholm, Vasily Kokorev, Michelle Jecmen, Damien Korber, Ryan Endsley, Richard Pan, Arghyadeep Basu, Jeremy Blaizot, Rychard Bouwens, Meriam Ezziati, Sylvain Heurtier, Kristen. B. W. McQuinn, Marcie Mun, Julian B. Munoz, Pascal Oesch, Joakim Rosdahl, Alberto Saldana-Lopez, Seiji Fujimoto
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7202180797