Observational evidence for AGNs feedback at parsec scale

TL;DR

This paper presents evidence that AGN feedback at parsec scales causes intermittent activity in low-luminosity AGNs through a heating and cooling cycle of accretion flows, explaining observed radio source populations.

Contribution

It introduces a mechanism linking AGN radiation feedback to episodic activity at parsec scales, supported by calculated timescales matching observations.

Findings

AGN radiation heats electrons at large radii, halting accretion.

Black hole activity oscillates with specific timescales.

Feedback at parsec scale influences AGN matter and energy output.

Abstract

In a hot accretion flow, the radiation from the innermost region of the flow propagates outward and heats the electrons at large radii via Compton scattering. It has been shown in previous works that if the radiation is strong enough, $L\ga 2%L_{\rm Edd}$, the electrons at the Bondi radius ($r_B\sim 10^5 r_s$) will be heated to be above the virial temperature thus the accretion will be stopped. The accretion will recover after the gas cools down. This results in the oscillation of the black hole activity. In this paper we show that this mechanism is the origin of the intermittent activity of some compact young radio sources. Such intermittency is required to explain the population of these sources. We calculate the timescales of the black hole oscillation and find that the durations of active and inactive phases are $3\times 10^4 (0.1/\alpha)(M/10^8\msun) (L/2%L_{\rm Edd})^{-1/2} {\rm yr}$ and $10^5(\alpha/0.1)(M/10^8\msun) {\rm yr}$, respectively, consistent with those required to explain observations. Such kind of feedback occurring at parsec scale should be common in low-luminosity AGNs and should be considered when we consider their matter and energy output.