Free-Streaming Length of Dark Matter from JWST Observations of 28 Strong Gravitational Lenses

D. Gilman; A. M. Nierenberg; T. Treu; K. N. Abazajian; T. Anguita; V. N. Bennert; A. J. Benson; S. Birrer; S. G. Djorgovski; X. Du; C. Gannon; S. F. Hoenig; R. E. Keeley; A. Kusenko; H. R. Larsson; M. Malkan; T. Morishita; V. Motta; L. A. Moustakas; P. Mozumdar; H. Paugnat; W. Sheu; D. Sluse; D. Stern; M. Stiavelli; D. Williams; K. C. Wong

doi:10.1103/qckh-cqrd

Free-Streaming Length of Dark Matter from JWST Observations of 28 Strong Gravitational Lenses

D. Gilman ^1,*, A. M. Nierenberg ^2,†, T. Treu ³, K. N. Abazajian ⁴, T. Anguita ⁵, V. N. Bennert ⁶, A. J. Benson ⁷, S. Birrer ⁸, S. G. Djorgovski⁹ et al.

X. Du ³, C. Gannon ², S. F. Hoenig ¹⁰, R. E. Keeley ², A. Kusenko ^3,11, H. R. Larsson ², M. Malkan ³, T. Morishita ¹², V. Motta ¹³, L. A. Moustakas ¹⁴, P. Mozumdar ^3,15, H. Paugnat ³, W. Sheu ³, D. Sluse ¹⁶, D. Stern¹⁴, M. Stiavelli ¹⁷, D. Williams ³, and K. C. Wong ¹⁸

¹Department of Astronomy and Astrophysics, University of Chicago, Chicago, Illinois 60637, USA
²University of California, Merced, 5200 N Lake Road, Merced, California 95341, USA
³Department of Physics and Astronomy, University of California, Los Angeles, California, 90095, USA
⁴Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA
⁵Instituto de Astrofisica, Departamento de Fisica y Astronomia, Universidad Andres Bello, Santiago, Chile
⁶Physics Department, California Polytechnic State University, San Luis Obispo, California 93407, USA
⁷Carnegie Institution for Science, Pasadena, California 91101, USA
⁸Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
⁹California Institute of Technology, Pasadena, California 91125, USA
¹⁰School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
¹¹Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
¹²IPAC, California Institute of Technology, MC 314-6, 1200 E. California Boulevard, Pasadena, California 91125, USA
¹³Instituto de Física y Astronomía, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso, Chile
¹⁴Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, California 91109, USA
¹⁵Department of Physics and Astronomy, University of California, Davis, 1 Shields Avenue, Davis, California 95616, USA
¹⁶STAR Institute, University of Liège, Quartier Agora, Allée du six Août 19c, 4000 Liège, Belgium
¹⁷Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA
¹⁸Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

^*Contact author: gilmanda@uchicago.edu
^†Contact author: anierenberg@ucmerced.edu

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Phys. Rev. Lett. 137, 081004 – Published 18 August, 2026

DOI: https://doi.org/10.1103/qckh-cqrd

Abstract

The formation of gravitationally bound overdensities of dark matter (DM), or halos, is a generic prediction of theories with particle DM. We present a measurement of halo properties in 28 quadruple image strong lens systems recently observed by JWST, and use these observations to constrain the free-streaming length, $λ_{FS}$ , of DM, a quantity that depends on the DM particle mass and formation mechanism. We improve on previous lensing analyses by simultaneously reconstructing extended lensed arcs with image positions and relative magnifications, enhancing sensitivity to perturbations by halos. Our analysis rules out deviations from the predictions of cold dark matter (CDM) on scales above $10^{7.2} M_{⊙}$ and $10^{7.4} M_{⊙}$ for subhalo abundance predicted by cosmological $N$ -body simulations and semianalytic models, respectively. These bounds correspond to upper limits $λ_{FS} < 6.0 kpc$ and $λ_{FS} < 7.0 kpc$ , and lower limits on the mass of a spin–1/2 thermal relic DM particle $m_{therm} > 7.4 keV$ and $m_{therm} > 6.5 keV$ . Conversely, assuming a negligible free-streaming length, as predicted by CDM, we measure a projected mass in subhalos around elliptical galaxies ${1.7}_{- 1.2}^{+ 2.6} \times 10^{7} M_{⊙} {kpc}^{- 2}$ at 95% confidence. These inferences confirm key predictions of the CDM paradigm.

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Free-Streaming Length of Dark Matter from JWST Observations of 28 Strong Gravitational Lenses

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JWST lensed quasar dark matter survey. III. Dark matter sensitive flux ratios and warm dark matter constraint from the full sample

JWST lensed quasar dark matter survey. IV. Stringent warm dark matter constraints from the joint reconstruction of extended lensed arcs and quasar flux ratios

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Free-Streaming Length of Dark Matter from JWST Observations of 28 Strong Gravitational Lenses

Abstract

Physics Subject Headings (PhySH)

See Also

JWST lensed quasar dark matter survey. III. Dark matter sensitive flux ratios and warm dark matter constraint from the full sample

JWST lensed quasar dark matter survey. IV. Stringent warm dark matter constraints from the joint reconstruction of extended lensed arcs and quasar flux ratios

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