Metal-rich trailing outflows uplifted by AGN bubbles in galaxy clusters

TL;DR

This study uses hydrodynamic simulations to demonstrate how AGN jets can uplift metal-rich gas in galaxy clusters, forming filamentary outflows that contribute to intracluster medium enrichment and match observational data.

Contribution

The paper provides the first detailed simulation evidence that AGN bubbles can uplift significant amounts of metal-rich gas via Darwin drift, aligning with observed outflow properties.

Findings

Outflows reach beyond 100 kpc with 10^10 M_sun of uplifted gas.

Outflow rates peak at nearly 100 M_sun/yr during the first 100 Myr.

Uplifted high-metallicity gas persists for hundreds of Myr, enriching the ICM.

Abstract

Recent Chandra X-ray observations of many galaxy clusters find evidence for hot metal-rich outflows preferentially aligned with the large-scale axes of X-ray cavities with typical outflow masses of around $10^{9} $ - $10^{10} M_{\odot}$. Here we perform a suite of three hydrodynamic simulations to investigate whether AGN jets could drive these metal-rich outflows in a representative cluster. By using both the tracer variable and virtual particle methods, and additionally following the gas metallicity evolution, we show that metal-rich gas initially located in central regions can indeed be uplifted by the AGN bubble to large distances, a phenomenon called Darwin drift in fluid mechanics, and forming a filamentary trailing outflow extending beyond $100$ kpc behind the bubble. The gas entrained in the trailing outflow is entirely outflowing with an average outflow rate of nearly $100M_{\odot}$/yr during the first $100$ Myr, and at later times, a growing lower part flows back towards the cluster center due to gravity. The outflow mass rises up to about $10^{10} M_{\odot}$ with entrained iron mass of about $10^{6} - 10^{7}M_{\odot}$, consistent with observations and predictions from the drift model. By the end of our simulation ($\sim 800$ Myr after the AGN event), several $10^{9}M_{\odot}$ of the uplifted high-metallicity gas still remains at large altitudes, potentially contributing to the enrichment of the bulk ICM and the broadening of central metallicity peaks observed in cool core clusters.