KIPAC Tea Talk: Model-Independent Measurements of Baryon Feedback with kSZ and Galaxy-Galaxy Lensing

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. In this talk, I will present model-independent measurements of the radial gas fraction profile around DESI galaxies, combining galaxy-galaxy lensing with the kinematic Sunyaev-Zel’dovich (kSZ) effect. I will introduce our new combined kSZ and lensing observable, with a modified kSZ filter designed to match the lensing ∆Σ observable, which allows us to make measurements of gas fractions directly. Applying this to DESI DR2 BGS and LRG samples with ACT DR6 CMB maps and the HSC Y3 shear catalogue, we find gas fractions strongly suppressed at small projected radii that recover toward the cosmic mean on larger scales. After correcting for the ACT beam with a simulation-calibrated, feedback-independent compensation factor, we detect baryon depletion at SNR = 17.1 (BGS) and 15.8 (LRG bin 1). I will also show comparisons to hydrodynamical simulations including Illustris, IllustrisTNG, SIMBA and FLAMINGO, spanning a range of feedback strengths and implementations. Finally, I will discuss the future direction of this work and the implications for baryon feedback and the power spectrum suppression.