The galaxy ultraviolet luminosity function from z = 7 to 20 in the COLIBRE simulations

Lu, S, Frenk, CS, Lacey, CG, Gebek, A, Schaye, J, Cole, S, Bose, S, Durrant, A, Andreadis, N, Baes, M, Benítez-Llambay, A, Chaikin, E, Correa, C, Crain, RA ORCID: 0000-0001-6258-0344, Huško, F, McGibbon, RJ, Ploeckinger, S, Richings, AJ, Schaller, M and Trayford, JW (2026) The galaxy ultraviolet luminosity function from z = 7 to 20 in the COLIBRE simulations. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711

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Abstract

James Webb Space Telescope (JWST) has enabled the detection of galaxies in the earliest stages of cosmic history. We compare the ultraviolet luminosity functions (UVLFs) at redshifts z = 7−20 predicted by a set of new cosmological hydrodynamical simulations, colibre (COLd ISM and Better REsolution), with observations, including those from JWST. The UV luminosities of colibre galaxies are derived using the radiative transfer code skirt, which tracks stellar emission and its processing through the multiphase interstellar medium and dust distribution predicted by colibre. We find that although colibre is consistent with the observed evolution of the stellar mass function up to z = 12, its dustattenuated UVLFsfallsystematically below the observations at the bright end: at the number density of 10−6 Mpc−3 mag−1, the brightest galaxies are underluminous by ≈ 1 mag at z = 7, increasing to ≈ 2.5 mag at z = 15. Accounting for observational uncertainties brings the colibre UVLFs closer to the observational data, but does not fully resolve the discrepancy. Ignoring dust attenuation allows colibre to produce sufficiently bright galaxies at 7 z 12, but at z = 15, colibre still underpredicts the luminosities of the brightest galaxies, indicating the need for additional physical mechanisms to boost the UV luminosities at the earliest cosmic epochs, such as a ‘top-heavy’ stellar initial mass function. We fit the colibre UVLFs with Schechterfunctions and calculate the evolution of the best-fitting parameters. We find that the galaxy number density decreases, the characteristic luminosity becomes fainter and the faint-end slope becomes steeper towards higher redshifts. The UV luminosity density decreases by a factor of several hundred from z = 7 to 15.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 51 Physical Sciences; 5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	18 September 2026
Date of first compliant Open Access:	22 October 2026
Date Deposited:	22 Oct 2026 13:11
Last Modified:	22 Oct 2026 13:11
DOI or ID number:	10.1093/mnras/stag1846
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29731

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