On the Role of the Hot Feedback Mode in Active Galactic Nuclei Feedback in an Elliptical Galaxy

Abstract

Depending on the value of the accretion rate, black hole accretion is divided into cold and hot modes. The two modes have distinctly different physics and correspond to two feedback modes. Most previous feedback works either focus only on one mode, or the accretion physics is not always properly adopted. Here, by performing hydrodynamical numerical simulations of AGN feedback in an elliptical galaxy, we show that including both is important, and gives different results from including just one or the other. We specifically focus on the wind and radiation (but neglecting the jet) feedback in the hot mode, to explore whether this particular mode of feedback can play any important feedback role. For this aim, we have run two test models. In one model, we always adopt the cold mode no matter what value the accretion rate is; in another model, we turn off the AGN once it enters into the hot mode. We have calculated the AGN light curves, black hole growth, star formation, and AGN energy duty-cycle; and compared the results with the model in which the two modes are correctly included. Important differences are found. For example, if we were to adopt only the cold mode, the total mass of newly formed stars would become two orders of magnitude smaller, and the fraction of energy ejected within the high accretion regime (i.e., L BH > 2%L Edd ) would be too small to be consistent with observations. We have also investigated the respective roles of wind and radiation in the hot mode.

Evidence for A Hot Wind from High-resolution X-ray Spectroscopic Observation of the Low-luminosity Active Galactic Nucleus in NGC 7213

“…Among the crucial open questions about LLAGN feedback is whether the hot wind can deposit its kinetic energy and momentum into a substantial volume of the host galaxy, as required to effectively quench star formation in cosmological simulations (Weinberger et al 2017;Pillepich et al 2018). Numerical simulations predict that the hot wind will interact with the circumnuclear medium, releasing its kinetic energy and momentum and potentially creating strong shocks (Yoon et al 2019). The 0.8-keV plasma found in the HETG spectrum might be evidence for such an interaction, which is likely the manifestation of a circumnuclear hot gas shock-heated by the outward propagating hot wind.…”

“…In fact, numerical simulations involving both the jet and the hot wind have shown that the momentum flux of the wind is always larger than that of jet (Yang et al 2021). The role of the hot wind in star formation and black hole growth has been investigated in detail by Yoon et al (2019). In the influential cosmological simulations of galaxy formation and evolution, IllustrisTNG (Weinberger et al 2017;Pillepich et al 2018), winds from weakly accreting SMBHs are invoked to quench star formation in intermediate-to high-mass galaxies.…”

Radiative feedback of low-Lbol/LEdd AGNs

“…In order to understand its relative importance, we show in the right panel of Figure 2 the power of different mechanisms as a function of accretion rate. The radiative heating (L BH in the plot) dominates over the kinematic power (Ė w in the plot) in the hot accretion mode (Yuan et al 2018;Gan et al 2019;Yoon et al 2019).…”

An Energetic Hot Wind from the Low-luminosity Active Galactic Nucleus M81*

“…Both theory and numerical simulations predict that a strong wind must exist in such hot accretion flows [3][4][5][6] . The wind is of special interest not only because it is an indispensable ingredient of accretion, but perhaps more importantly, it is believed to play a crucial role in the evolution of the host galaxy via the so-called kinetic mode AGN feedback 7,8 . Observational evidence for this wind, however, remains scarce and indirect [9][10][11][12] .…”

“…The bulk of the wind momentum and kinetic energy should be deposited into the interstellar medium (ISM) due to the wide opening angle of the wind, thus providing an effective feedback to the host galaxy and regulating the growth of the SMBH 7,8 . This is supported by the existence of the 0.9-keV component in the X-ray spectrum, which is likely the result of the outward propagating wind shock-heating the ISM.…”