Accurate cosmology from upcoming weak lensing surveys relies on knowledge of the total matter power spectrum at percent level at scales k < 10 h/Mpc, for which modelling the impact of baryonic physics is crucial. We compare measurements of the total matter power spectrum from the Horizon cosmological hydrodynamical simulations: a dark matter-only run, one with full baryonic physics, and another lacking Active Galactic Nuclei (AGN) feedback. Baryons cause a suppression of power at k ≃ 10 h/Mpc of < 15% at z = 0, and an enhancement of a factor of a few at smaller scales due to the more efficient cooling and star formation. The results are sensitive to the presence of the highest mass haloes in the simulation and the distribution of dark matter is also impacted up to a few percent. The redshift evolution of the effect is non-monotonic throughout z = 0 − 5 due to an interplay between AGN feedback and gas pressure, and the growth of structure. We investigate the effectiveness of an analytic "baryonic correction model" in describing our results. We require a different redshift evolution and propose an alternative fitting function with 4 free parameters that reproduces our results within 5%. Compared to other simulations, we find the impact of baryonic processes on the total matter power spectrum to be smaller at z = 0. Correspondingly, our results suggest that AGN feedback is not strong enough in the simulation. Total matter power spectra from the Horizon simulations are made publicly available at https://www.horizon-simulation.org/catalogues.html.

Multi-phase filamentary structures around Brightest Cluster Galaxies (BCG) are likely a key step of AGN-feedback. We observed molecular gas in 3 cool cluster cores: Centaurus, Abell S1101, and RXJ1539.5 and gathered ALMA (Atacama Large Millimeter/submillimeter Array) and MUSE (Multi Unit Spectroscopic Explorer) data for 12 other clusters. Those observations show clumpy, massive and long, 3-25 kpc, molecular filaments, preferentially located around the radio bubbles inflated by the AGN (Active Galactic Nucleus). Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the Hα/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 to 7 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100-400 km s −1 , with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin (as yet) unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the filament's radial extent, r fil , with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short cooling time region, where t cool /t ff <20 (9 of 13 sources). The range t cool /t ff , 8-23 at r fil , is likely due to (i) a more complex gravitational potential affecting the free-fall time t ff (sloshing, mergers. . . ); (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time t cool . For some of the sources, r fil lies where the ratio of the cooling time to the eddy-turnover time, t cool /t eddy , is approximately unity.