A GLIMPSE of Dark Matter: JWST Constraints on Early Structure Formation
Abstract
While we have a solid understanding of how dark matter (DM) behaves during recombination (z∼ 103) and in the late universe (z≲ a few), much less is known about intermediate times, when the first galaxies formed. These galaxies provide a powerful handle on DM through structure formation, as halos have to exist to host luminous sources. Here we use recent determinations of the UV luminosity function from the James Webb Space Telescope (JWST) GLIMPSE lensing program, along with legacy Hubble and Subaru data, to test the small-scale behavior of DM during the epoch of reionization (z∼ 7). Marginalizing over astrophysical uncertainties, we find the matter power spectrum to be consistent with the cold-DM prediction down to sub-Mpc scales, with 1σ uncertainties of 0.2 dex at k=3−9 Mpc−1 and 0.5 dex at k=9−27 Mpc−1, the smallest scales probed at these early times. For thermal-relic warm DM we constrain mWDM > 3.2 keV (95% CL), independent of lower-z probes. Our results test small-scale structure formation in a new redshift window and demonstrate the promise of JWST to constrain the nature of DM.
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BibTeX
@misc{munoz2026glimpse,
title = {{A GLIMPSE of Dark Matter: JWST Constraints on Early Structure Formation}},
author = {Julian B. Muñoz and John Chisholm and Seiji Fujimoto and Tiger Yu-Yang Hsiao and Kristen B. W. McQuinn and Priyamvada Natarajan and A. Saldana-Lopez and Hakim Atek and Arghyadeep Basu and Danielle Berg and Ryan Endsley and Lukas J. Furtak and Damien Korber and Rohan P. Naidu and Richard Pan and Daniel Schaerer},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37751},
eprint = {2610.37751},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37751},
}
RIS
TY - UNPB
TI - A GLIMPSE of Dark Matter: JWST Constraints on Early Structure Formation
AU - Julian B. Muñoz
AU - John Chisholm
AU - Seiji Fujimoto
AU - Tiger Yu-Yang Hsiao
AU - Kristen B. W. McQuinn
AU - Priyamvada Natarajan
AU - A. Saldana-Lopez
AU - Hakim Atek
AU - Arghyadeep Basu
AU - Danielle Berg
AU - Ryan Endsley
AU - Lukas J. Furtak
AU - Damien Korber
AU - Rohan P. Naidu
AU - Richard Pan
AU - Daniel Schaerer
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37751
UR - https://arxiv.org/abs/2610.37751
AB - While we have a solid understanding of how dark matter (DM) behaves during recombination (z∼ 10^3) and in the late universe (z≲ a few), much less is known about intermediate times, when the first galaxies formed. These galaxies provide a powerful handle on DM through structure formation, as halos have to exist to host luminous sources. Here we use recent determinations of the UV luminosity function from the James Webb Space Telescope (JWST) GLIMPSE lensing program, along with legacy Hubble and Subaru data, to test the small-scale behavior of DM during the epoch of reionization (z∼ 7). Marginalizing over astrophysical uncertainties, we find the matter power spectrum to be consistent with the cold-DM prediction down to sub-Mpc scales, with 1σ uncertainties of 0.2 dex at k=3−9 Mpc^−1 and 0.5 dex at k=9−27 Mpc^−1, the smallest scales probed at these early times. For thermal-relic warm DM we constrain m_WDM > 3.2 keV (95% CL), independent of lower-z probes. Our results test small-scale structure formation in a new redshift window and demonstrate the promise of JWST to constrain the nature of DM.
ER -