Massive outflow properties suggest AGN fade slowly

TL;DR

This paper demonstrates that correlations between AGN outflow properties and luminosity can persist during AGN fading phases, implying outflows evolve slowly and can inform us about AGN activity history.

Contribution

It shows that outflow-luminosity correlations are maintained during AGN fade, providing insights into outflow evolution and AGN activity timescales.

Findings

Correlations persist during AGN fading if luminosity declines as a power law with exponent ~1.

Outflows with lower momentum and energy rates than expected may be common and hard to detect.

Observations of outflow properties can help reconstruct AGN activity histories.

Abstract

Massive large-scale AGN outflows are an important element of galaxy evolution, being a way through which the AGN can affect most of the host galaxy. However, outflows evolve on timescales much longer than typical AGN episode durations, therefore most AGN outflows are not observed simultaneously with the AGN episode that inflated them. It is therefore remarkable that rather tight correlations between outflow prop- erties and AGN luminosity exist. In this paper, I show that such correlations can be preserved during the fading phase of the AGN episode, provided that the AGN lumi- nosity evolves as a power law with exponent $\alpha_{\rm d} \sim 1$ at late times. I also show that subsequent AGN episodes that illuminate an ongoing outflow are unlikely to produce outflow momentum or energy rates rising above the observed correlations. However, there may be many difficult-to-detect outflows with momentum and energy rates lower than expected from the current AGN luminosity. Detailed observations of AGN out- flow properties might help constrain the activity histories of typical and/or individual AGN.