Feedback from active galactic nuclei and stellar processes changes the matter distribution on small scales, leading to significant systematic uncertainty in weak lensing constraints on cosmology. We investigate how the observable properties of group-scale halos can constrain feedback’s impact on the matter distribution using Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS). Extending the results of previous work to smaller halo masses and higher wavenumber, k, we find that the baryon fraction in halos contains significant information about the impact of feedback on the matter power spectrum. We explore how the thermal Sunyaev Zel’dovich (tSZ) signal from group-scale halos contains similar information. Using recent Dark Energy Survey (DES) weak lensing and Atacama Cosmology Telescope (ACT) tSZ cross-correlation measurements and models trained on CAMELS, we obtain 10% constraints on feedback effects on the power spectrum at k ∼ 5 h/Mpc. We show that with future surveys, it will be possible to constrain baryonic effects on the power spectrum to $\mathcal {O}(<1\%)$ at k = 1 h/Mpc and $\mathcal {O}(3\%)$ at k = 5 h/Mpc using the methods that we introduce here. Finally, we investigate the impact of feedback on the matter bispectrum, finding that tSZ observables are highly informative in this case.

Extracting information from the total matter power spectrum with the precision needed for upcoming large cosmological surveys requires unraveling the complex effects of galaxy formation processes on the distribution of matter. In this work, we investigate the impact of baryonic physics on matter clustering at 𝑧 = 0 using a large library of power spectra from the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project, containing thousands of (25 ℎ −1 Mpc) 3 volume realizations with varying cosmology, initial random field, stellar and AGN feedback strength, sub-grid model implementation, and (magneto)hydrodynamics methods. We show that baryonic physics can profoundly affect matter clustering on scales 𝑘 0.1 ℎ Mpc −1 and the magnitude of this effect is highly dependent on the details of the galaxy formation implementation and variations of cosmological and astrophysical parameters. Increasing AGN feedback strength decreases halo baryon fractions and yields generally stronger suppression of power relative to N-body simulations, while stronger stellar feedback often results in weaker overall effects by suppressing black hole growth and therefore the impact of AGN feedback. We find a broad correlation between mean baryon fraction of massive halos (𝑀 200c > 10 13.5 M /ℎ) and suppression of matter clustering but with significant scatter compared to previous work owing to wider exploration of feedback parameters and cosmic variance effects. We show that a random forest regressor trained on the baryon content and abundance of halos across the full mass range 10 10 ≤ 𝑀 halo /M ℎ −1 < 10 14 can predict the effect of galaxy formation on the matter power spectrum on scales 𝑘 = 0.5-20 ℎ Mpc −1 , providing access to cosmological information in the highly non-linear regime.

Feedback from active galactic nuclei and stellar processes changes the matter distribution on small scales, leading to significant systematic uncertainty in weak lensing constraints on cosmology. We investigate how the observable properties of group-scale halos can constrain feedback's impact on the matter distribution using Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS). Extending the results of previous work to smaller halo masses and higher wavenumber, k, we find that the baryon fraction in halos contains significant information about the impact of feedback on the matter power spectrum. We explore how the thermal Sunyaev Zel'dovich (tSZ) signal from group-scale halos contains similar information. Using recent Dark Energy Survey (DES) weak lensing and Atacama Cosmology Telescope (ACT) tSZ cross-correlation measurements and models trained on CAMELS, we obtain 10% constraints on feedback effects on the power spectrum at k ∼ 5 h/Mpc. We show that with future surveys, it will be possible to constrain baryonic effects on the power spectrum to O(< 1%) at k = 1 h/Mpc and O(3%) at k = 5 h/Mpc using the methods that we introduce here. Finally, we investigate the impact of feedback on the matter bispectrum, finding that tSZ observables are highly informative in this case.