Model-Independent Measurement of Baryon Gas Fractions through Galaxy-Galaxy Lensing and the Kinematic Sunyaev-Zel'dovich Effect
astro-ph.CO, astro-ph.GA
Submitted: 2026-09-18
Updated: 2026-09-27
Comments: 31 pages, 26 figures, comments welcome
License: http://creativecommons.org/licenses/by/4.0/
The gist: Baryon feedback is a leading source of systematic uncertainty for cosmology from weak lensing, but measurements of the gas distribution around galaxies have largely relied on parametric profile
Terminology
Abstract
Baryon feedback is a leading source of systematic uncertainty for cosmology from weak lensing, but measurements of the gas distribution around galaxies have largely relied on parametric profile models or simulation-calibrated frameworks. We present model independent measurements of the radial gas fraction profile around galaxies, combining galaxy-galaxy lensing and kinematic Sunyaev-Zel'dovich (kSZ) effect. We introduce a method that applies the same radial ΔΣ aperture filter to both the galaxy-galaxy lensing shear field and the velocity-weighted kSZ temperature maps; their ratio directly yields ΔΣ filtered gas fraction f gas(R), the ratio of ionized gas to total matter as a function of projected radius. We apply this approach to DESI DR2 Bright Galaxy Survey (BGS, about0.26) and Luminous Red Galaxy (LRG, 0.4<z<1.1) samples, using ACT DR6 component-separated CMB maps for kSZ and the HSC Year 3 shear catalog for weak lensing. After correcting for ACT beam suppression using a simulation-calibrated compensation factor, we detect baryon depletion relative to the cosmic mean baryon fraction at SNR = 17.1 (BGS) and SNR = 15.8 (LRG bin 1). Comparison with six hydrodynamical simulations from the Illustris, IllustrisTNG, SIMBA, and FLAMINGO suites shows that no single feedback prescription reproduces the observed radial gas distribution across all scales, with the measurements falling between the strongest (Illustris-1) and weaker prescriptions. We caution that comparisons between the South Galactic Cap (SGC) and North Galactic Cap (NGC) show evidence of unexplained residual systematics in kSZ in one redshift bin. The ratio is robust against splits by stellar mass and satellite versus centrals. These results establish ΔΣ filtering of kSZ versus weak lensing signal as a model-independent probe of the baryon distribution around galaxies.
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