http://arxiv.org/abs/2304.12696
Powerful winds at accretion disk scales have been observed in the past 20 years in many AGN, the so called Ultra-Fast Outflows (UFOs). Outflows are intimately related to mass accretion due to the conservation of angular momentum, and therefore are a key ingredient of most accretion disk models around BHs. At the same time, nuclear winds and outflows can provide the feedback which regulates the joint BH and galaxy growth. We reconsider UFO observations in the framework of the Magneto-Hydrodynamic Disk Wind (MHDW) scenario and study their statistical properties. We derive the typical wind-activity history in our sources by assuming that it can be statistically described by population functions. We study the statistical properties of UFOs from the literature and derive the distribution functions of the ratio $\bar \omega$ between the mass outflow and inflow rates, and the ratio $\lambda_w$ between the mass outflow and the Eddington accretion rates. We study the links between $\bar \omega$ and $\lambda_w$ and the Eddington ratio $\lambda={L_{bol}}/{L_{Edd}}$. We find that the distribution functions of $\bar \omega$ and $\lambda_w$ can be described as power laws above some threshold, suggesting that there may be many wind sub-events for each major wind event in each AGN activity cycle, which is a fractal behaviour in agreement with current MHDW and Chaotic Cold Accretion theories. We then introduce a simple cellular automaton to investigate how the dynamical properties of an idealized disk-wind system changes following the introduction of simple feedback rules. We find that without feedback the system is over-critical. Conversely, if feedback is present, the system can be driven toward self organized criticality. Our results corroborate the hypothesis that AGN feedback is a necessary key ingredient in disk-wind systems, and thus, in shaping the co-evolution of galaxies and supermassive BHs.
F. Fiore, M. Gaspari, A. Luminari, et. al.
Wed, 26 Apr 23
12/62
Comments: Back to Astronomy & Astrophysics, revised manuscript after referee report