Raining on black holes and massive galaxies: the top-down multiphase condensation model

TL;DR

This paper presents a new top-down multiphase condensation model for plasma halos in massive galaxies, explaining the formation of warm and cold filaments and their role in chaotic cold accretion and AGN feedback.

Contribution

It introduces high-resolution 3D simulations revealing the multiphase condensation cascade and its impact on black hole accretion and galaxy evolution.

Findings

Warm filaments extend several kpc and form a skin around neutral filaments.

Cold molecular clouds with masses up to 10^7 solar masses form from warm filaments.

Chaotic cold accretion (CCA) leads to recurrent, boosted black hole accretion rates.

Abstract

The atmospheres filling massive galaxies, groups, and clusters display remarkable similarities with rainfalls. Such plasma halos are shaped by AGN heating and subsonic turbulence (~150 km/s), as probed by Hitomi. The new 3D high-resolution simulations show the soft X-ray (< 1 keV) plasma cools rapidly via radiative emission at the high-density interface of the turbulent eddies, stimulating a top-down condensation cascade of warm, $10^4$ K filaments. The ionized (optical/UV) filaments extend up to several kpc and form a skin enveloping the neutral filaments (optical/IR/21-cm). The peaks of the warm filaments further condense into cold molecular clouds (<50 K; radio) with total mass up to several $10^7$ M$_\odot$, i.e., 5/50$\times$ the neutral/ionized masses. The multiphase structures inherit the chaotic kinematics and are dynamically supported. In the inner 500 pc, the clouds collide in inelastic way, mixing angular momentum and leading to chaotic cold accretion (CCA). The BHAR can be modeled via quasi-spherical viscous accretion with collisional mean free path ~100 pc. Beyond the inner kpc region pressure torques drive the angular momentum transport. In CCA, the BHAR is recurrently boosted up to 2 dex compared with the disc evolution, which arises as turbulence is subdominant. The CCA BHAR distribution is lognormal with pink noise power spectrum characteristic of fractal phenomena. The rapid self-similar CCA variability can explain the light curve variability of AGN and HMXBs. An improved criterium to trace thermal instability is proposed. The 3-phase CCA reproduces crucial observations of cospatial multiphase gas in massive galaxies, as Chandra X-ray images, SOAR H$\alpha$ warm filaments and kinematics, Herschel [C$^+$] emission, and ALMA giant molecular associations. CCA plays key role in AGN feedback, AGN unification/obscuration, the evolution of BHs, galaxies, and clusters.