The impact of baryons on the matter power spectrum from the Horizon-AGN cosmological hydrodynamical simulation

TL;DR

The paper analyzes how baryonic physics, especially AGN feedback, reshapes the total matter power spectrum using the Horizon-AGN suite (full baryons, no AGN, and DM-only). By computing high-resolution power spectra and comparing to a baryonic correction framework, the authors show a non-monotonic redshift evolution and a net suppression of 5–15% at intermediate scales by z=0, with an accompanying small-scale boost from cooling. They develop a redshift-dependent four-parameter BC-like model that reproduces their results within 5% and discuss how Horizon-AGN compares to other hydrodynamical simulations, finding generally smaller baryonic impacts. The results highlight the importance of evolving baryonic models for weak lensing analyses and provide public power-spectrum data to aid cosmological forecasts and systematics studies.

Abstract

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 $k\simeq 10$ $h/$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

Figures (13)

• Figure 1: The impact of AGN feedback in the total matter power spectrum from the Horizon set across cosmic time, $0\leq z<6$. Darker colours correspond to lower redshifts. At intermediate scales ($k \sim 2\,h/$Mpc), the AGN feedback suppression diminishes slightly from $z=1$ to $z=0$, an effect that we attribute to AGN feedback being insufficient to expel gas from the growing potential well of the most massive haloes.
• Figure 2: The fractional impact of baryons on the total matter power spectrum when comparing the Horizon-noAGN run (lacking AGN feedback) to the Horizon-DM run.
• Figure 3: The fractional impact of baryons on the total matter power spectrum when comparing the Horizon-AGN run (with AGN feedback) to the Horizon-DM run. Results are split in two panels for different redshift ranges: $z\leq 3$ (left panel) and $z\geq 3$ (right panel).
• Figure 4: The fractional power spectrum of the dark matter component from the Horizon-AGN (solid) and the Horizon-noAGN (dashed) runs in the redshift range between $0\leq z< 5$. Only selected redshifts are shown for the Horizon-noAGN runs.
• Figure 5: The impact of cosmic variance on the total matter power spectrum (left) and on the power spectrum of the dark matter component (right) at $z=0$. The results for the full volume are shown in thick solid black; all other curves correspond to the $8$ sub-volumes of the box. The large-scale excess is discussed in Appendix \ref{['app_growth']}. We have not applied any correction for shot noise in this figure, given that it is sub-dominant at this redshift.