Dynamics and Morphology of Cold Gas in Fast, Radiatively Cooling Outflows: Constraining AGN Energetics with Horseshoes

Abstract

Warm ionized and cold neutral outflows with velocities exceeding $100{\mathrm{km}\mathrm{s}}^{-1}$ are commonly observed in galaxies and clusters. Theoretical studies however indicate that ram pressure from a hot wind, driven either by the central active galactic nucleus (AGN) or a starburst, cannot accelerate existing cold gas to such high speeds without destroying it. In this work we explore a different scenario, where cold gas forms in a fast, radiatively cooling outflow with temperature $T\lesssim 10^7\mathrm{K}$. Using 3D hydrodynamic simulations, we demonstrate that cold gas continuously fragments out of the cooling outflow, forming elongated filamentary structures extending tens of kiloparsecs. For a range of physically relevant temperature and velocity configurations, a ring of cold gas perpendicular to the direction of motion forms in the outflow. This naturally explains the formation of transverse cold gas filaments such as the blue loop and the horseshoe filament in the Perseus cluster. Based on our results, we estimate that the AGN outburst responsible for the formation of these two features drove bipolar outflows with velocity $>2,000{\mathrm{km}\mathrm{s}}^{-1}$ and total kinetic energy $>8\times 10^{57}\mathrm{erg}$ about $\sim 10$ Myr ago. We also examine the continuous cooling in the mixing layer between hot and cold gas, and find that radiative cooling only accounts for $\sim 10\%$ of the total mass cooling rate, indicating that observations of soft X-ray and FUV emission may significantly underestimate the growth of cold gas in the cooling flow of galaxy clusters.

8 pages, 3 figures, accepted for publication in ApJL

References in corpus (7)

• The Launching of Cold Clouds by Galaxy Outflows I: Hydrodynamic Interactions with Radiative Cooling
• Cold molecular gas in the Perseus cluster core - Association with X-ray cavity, Halpha filaments and cooling flow -
• Magnetic support of the optical emission line filaments in NGC 1275
• Formation of cold filaments in cooling flow clusters
• Cold gas in the Perseus cluster core: Excitation of molecular gas in filaments
• OVI Observations of Galaxy Clusters: Evidence for Modest Cooling Flows
• The Origin and Kinematics of Cold Gas in Galactic Winds: Insight from Numerical Simulations

Cited by in corpus (7)

• Gas condensation in Brightest Group Galaxies unveiled with MUSE
• Bubble-driven Gas Uplift in Galaxy Clusters and its Velocity Features
• Radio jet-ISM interaction and positive radio-mechanical feedback in Abell 1795
• Signature of Supersonic Turbulence in Galaxy Clusters Revealed by AGN-driven H$\alpha$ Filaments
• The cavity of 3CR 196.1: H$\alpha$ emission spatially associated with an X-ray cavity
• The abundance and origin of cool gas in galaxy clusters in the TNG-Cluster simulation
• Testing the Limits of AGN Feedback and the Onset of Thermal Instability in the Most Rapidly Star Forming Brightest Cluster Galaxies