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

@misc{lu2026galaxy,
  title = {{The galaxy ultraviolet luminosity function from $z=7$ to $20$ in the COLIBRE simulations}},
  author = {Shengdong Lu and Carlos S. Frenk and Cedric G. Lacey and Andrea Gebek and Joop Schaye and Shaun Cole and Sownak Bose and Anna Durrant and Nick Andreadis and Maarten Baes and Alejandro Benítez-Llambay and Evgenii Chaikin and Camila Correa and Robert A. Crain and Filip Huško and Robert J. McGibbon and Sylvia Ploeckinger and Alexander J. Richings and Matthieu Schaller and James W. Trayford},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2605.06782},
  eprint = {2605.06782},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.06782},
}

TY  - UNPB
TI  - The galaxy ultraviolet luminosity function from z=7 to $20$ in the COLIBRE simulations
AU  - Shengdong Lu
AU  - Carlos S. Frenk
AU  - Cedric G. Lacey
AU  - Andrea Gebek
AU  - Joop Schaye
AU  - Shaun Cole
AU  - Sownak Bose
AU  - Anna Durrant
AU  - Nick Andreadis
AU  - Maarten Baes
AU  - Alejandro Benítez-Llambay
AU  - Evgenii Chaikin
AU  - Camila Correa
AU  - Robert A. Crain
AU  - Filip Huško
AU  - Robert J. McGibbon
AU  - Sylvia Ploeckinger
AU  - Alexander J. Richings
AU  - Matthieu Schaller
AU  - James W. Trayford
PY  - 2026
DA  - 2026/09/28
PB  - arXiv
DO  - 10.48550/arxiv.2605.06782
UR  - https://arxiv.org/abs/2605.06782
AB  - 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, 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 multi-phase 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 dust-attenuated UVLFs fall systematically 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 Schechter functions and calculate the evolution of the best-fit 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 z = 15.
ER  -