Abstract
We conduct a pseudo-$C_\ell$ analysis of the tomographic cross-correlation
between 1000 deg$^2$ of weak lensing data from the Kilo-Degree Survey
(KiDS-1000) and the thermal Sunyaev-Zeldovich (tSZ) effect measured by Planck
and the Atacama Cosmology Telescope (ACT). Using HMx, a halo-model-based
approach that consistently models the gas, star, and dark matter components, we
are able to derive constraints on both cosmology and baryon feedback for the
first time from this data, marginalising over redshift uncertainties, intrinsic
alignment of galaxies, and contamination by the cosmic infrared background
(CIB). We find our results to be insensitive to the CIB, while intrinsic
alignment provides a small but significant contribution to the lensing--tSZ
cross-correlation. The cosmological constraints are consistent with those of
other low-redshift probes and prefer strong baryon feedback. The inferred
amplitude of the lensing--tSZ cross-correlation signal, which scales as
$\sigma_8(Ømega_m/0.3)^0.2$, is low by $2\,\sigma$ compared to
the primary cosmic microwave background constraints by Planck. The lensing--tSZ
measurements are then combined with pseudo-$C_\ell$ measurements of KiDS-1000
cosmic shear into a novel joint analysis, accounting for the full
cross-covariance between the probes, providing tight cosmological constraints
by breaking parameter degeneracies inherent to both probes. The joint analysis
gives an improvement of 40% on the constraint of
$S_8=\sigma_8Ømega_\mathrmm/0.3$ over cosmic shear alone, while
providing constraints on baryon feedback consistent with hydrodynamical
simulations, demonstrating the potential of such joint analyses with baryonic
tracers like the tSZ effect. We discuss remaining modelling challenges that
need to be addressed if these baryonic probes are to be included in future
precision-cosmology analyses.
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