UV line-driven disc wind as the origin of UltraFast Outflows in AGN

Abstract

UltraFast Outflows (UFO) are observed in some active galactic nuclei (AGN), with blueshifted and highly ionised Fe-K absorption features. AGN typically have a UV bright accretion flow, so UV line driving is an obvious candidate for launching these winds. However this mechanism requires material with UV opacity, in apparent conflict with the observed high ionisation state of the wind. In this paper we synthesise the X-ray energy spectra resulting from different lines of sight through a state of the art radiation hydrodynamics UV line driven disc wind simulation. We demonstrate that there are some lines of sight which only intercept highly ionised and fast outflowing material. The cooler material required for the UV line driving acceleration is out of the line of sight, close to the disc, shielded from the X-rays by a failed wind. We fit these simulated wind spectra to data from the archetypal UFO source PG 1211+143 and show that they broadly reproduce the depth and velocity of the iron absorption lines seen. This directly demonstrates that UV line driving is a viable mechanism to launch even the fastest UFOs. We simulate microcalorimeter observations of this wind and show that their high energy resolution can resolve the detailed structure in the wind and recover the wind energetics when combined with models which correctly estimate the line formation radius of the wind. New data from microcalorimeters will pave the way for physical predictions of AGN wind feedback in cosmological simulations.

Dramatic changes in the observed velocity of the accretion disk wind in MCG-03-58-007 are revealed by XMM-Newton and NuSTAR

“…This is the first time where we have observed a substantial variability of the outflowing velocity in a disk wind, which dropped from v out /c ∼ −0.2 (as measured in the first three observations) to v out /c ∼ −0.074 in just 16 days. We conclude that such a dramatic and fast variability of the outflowing velocity could be due to the acceleration of the wind, as recently proposed by Mizumoto et al (2021). Here, the faster wind, seen in the first three observations, is already accelerated to v out /c ∼ −0.2, while in the last observation our line of sight intercepts only the slower, pre-accelerated streamline.…”

“…1). The only other possibility is that there was a more substantial decrease of the luminosity in between OBS3 and OBS4; however, this is highly unlikely as none of the previous observations caught MCG-03-58-007 in such a faint state (see Table 2 in B21 We now consider the results obtained by Mizumoto et al (2021) on the X-ray spectra predicted from the most recent hydrodynamics simulations of UV line driven disc winds, using a specific prescription for the X-ray opacity (Nomura et al 2020). The above authors compute the evolution of the line driven wind properties (in terms of ionization, density and velocity) as a function of the wind radius (e. g. see Fig.…”

“…Since MCG-03-58-007 is a highly obscured AGN, we cannot directly measure this luminosity, we therefore assumed as in B18 that it is of the order of 1/3 of the bolometric luminosity of 3 × 10 45 erg s −1 ated through UV line driving (Mizumoto et al 2021).…”

“…In the Xray band we can improve our accuracy on the estimates of the energetics by applying self consistent disk wind models. Recently, various groups have been developing new models for radiatively driven (Sim et al 2008(Sim et al , 2010aHagino et al 2015Hagino et al , 2016Nomura & Ohsuga 2017;Nomura et al 2020;Mizumoto et al 2021) as well as MHD winds. (Fukumura et al 2010(Fukumura et al , 2015Kazanas et al 2012).…”

Qwind3: UV line-driven accretion disc wind models for AGN feedback

“…This is too ionised to allow even H-and He-like iron to give visible atomic features in this high velocity gas, although these species may exist at smaller radii where the material is denser. We will explore the observational impact of this in a future work, specifically assessing whether UV line-driving can be the origin of the ultra-fast outflows seen in some AGN (see also Mizumoto et al 2021).…”