Tilman tells us about his recent work combining KiDS cosmic shear measurements and Planck measurements of the thermal Sunyaev Zeldovich (tSZ) effect from the cosmic microwave background scattering off hot gas in galaxy clusters and galaxy groups. The long term goal is to use cross-correlation of shear and the tSZ effect to help constrain (or essentially measure) baryon feedback and thus push to smaller scales.

In this work, they don’t push to smaller scales, partially because doing so would require many more careful checks and partially because Planck’s beam isn’t small enough to make it worthwhile. However they still gain approximately two times tighter constraints in the Ωm vs σ8 plane compared to shear alone because of the additional information available in tSZ about where matter clusters, and what the baryons are actually up to.

The results themselves are awesome (error bars shrinking by a factor of two is impressive enough) but also are a great proof of concept that we can measure baryon feedback like this (and don’t have to necessarily predict it entirely from first principles).

With CMB Stage 4 beam sizes and sky coverage, it will be fascinating to see what can be done with this method…

Tilman: https://tilman.troester.space/
Paper: https://arxiv.org/abs/2109.04458