Inverse Compton X-ray signature of AGN feedback

TL;DR

This paper models the Inverse Compton X-ray emission from ultra-fast outflows in AGN, suggesting that observed soft X-ray excesses may originate from shock emissions and providing a new way to study AGN feedback.

Contribution

It introduces calculations of Inverse Compton spectra from AGN outflow shocks, distinguishing between one-temperature and two-temperature regimes and linking observations to feedback mechanisms.

Findings

1T shock emission likely not observed in current AGN data.

2T shock emission could explain the soft X-ray excess in AGN.

UFOs are energy-driven and significantly impact host galaxy gas.

Abstract

Bright AGN frequently show ultra-fast outflows (UFOs) with outflow velocities vout ~0.1c. These outflows may be the source of AGN feedback on their host galaxies sought by galaxy formation modellers. The exact effect of the outflows on the ambient galaxy gas strongly depends on whether the shocked UFOs cool rapidly or not. This in turn depends on whether the shocked electrons share the same temperature as ions (one temperature regime; 1T) or decouple (2T), as has been recently suggested. Here we calculate the Inverse Compton spectrum emitted by such shocks, finding a broad feature potentially detectable either in mid-to-high energy X-rays (1T case) or only in the soft X-rays (2T). We argue that current observations of AGN do not seem to show evidence for the 1T component. The limits on the 2T emission are far weaker, and in fact it is possible that the observed soft X-ray excess of AGN is partially or fully due to the 2T shock emission. This suggests that UFOs are in the energy-driven regime outside the central few pc, and must pump considerable amounts of not only momentum but also energy into the ambient gas. We encourage X-ray observers to look for the Inverse Compton components calculated here in order to constrain AGN feedback models further.