Matter Clustering in Astrid: Reduced Baryonic Suppression from Realistic Black Hole Dynamics

TL;DR

This study shows that realistic black hole dynamics in simulations reduce baryonic suppression of matter clustering, challenging previous models and implications for cosmology.

Contribution

It introduces a more physical black hole dynamical model in simulations, reducing artificial feedback effects and altering matter clustering predictions.

Findings

No significant suppression at z=0 in Astrid-DMO

Weaker suppression than other simulations due to black hole treatment

Reconciliation with CMB cosmology is more challenging with AGN feedback

Abstract

Baryonic feedback from active galactic nuclei (AGN) is often invoked as a major source of suppression in the matter power spectrum, with implications for precision cosmology and the $S_8$ tension. We present Astrid-DMO, the dark matter-only counterpart to the large-volume Astrid hydrodynamical simulation, and measure baryonic effects through $P_{\rm hydro}(k)/P_{\rm DMO}(k)$. We find no significant suppression at $z=0$ and mild suppression at $z=0.2$, weaker than in other state-of-the-art simulations. Using controlled small-volume runs, we identify a key driver of this discrepancy: the treatment of black hole (BH) dynamics. The widely used BH repositioning scheme artificially enhances BH mergers and boosts kinetic AGN feedback (e.g., by a factor of $2$ at $z=1.5$), leading to overly strong suppression. By contrast, a more physical dynamical friction model reduces feedback efficiency and weakens clustering suppression. Consequently, reconciling large-scale structure measurements with cosmic microwave background (CMB)-inferred $\Lambda$CDM cosmology with AGN feedback becomes more challenging. Although strengthening AGN feedback can increase suppression, in our model this induces tensions with the observed galaxy stellar mass and AGN luminosity functions. These results motivate considering either new non-baryonic physics that suppresses late-time matter clustering, or novel mechanisms that can efficiently eject gas from halos without compromising other galaxy properties.