Hot Atmospheres, Cold Gas, AGN Feedback and the Evolution of Early Type Galaxies: A Topical Perspective

Abstract

Most galaxies comparable to or larger than the mass of the Milky Way host hot, X-ray emitting atmospheres, and many such galaxies are radio sources. Hot atmospheres and radio jets and lobes are the ingredients of radiomechanical active galactic nucleus (AGN) feedback. While a consensus has emerged that such feedback suppresses cooling of hot cluster atmospheres, less attention has been paid to massive galaxies where similar mechanisms are at play. Observation indicates that the atmospheres of elliptical and S0 galaxies were accreted externally during the process of galaxy assembly and augmented significantly by stellar mass loss. Their atmospheres have entropy and cooling time profiles that are remarkably similar to those of central cluster galaxies. About half display filamentary or disky nebulae of cool and cold gas, much of which has likely cooled from the hot atmospheres. We review the observational and theoretical perspectives on thermal instabilities in galactic atmospheres and the evidence that AGN heating is able to roughly balance

The relationship between black hole mass and galaxy properties: examining the black hole feedback model in IllustrisTNG

“…These results show that the existence of a quiescent population in TNG depends on the model's implementation of low accretion rate kinetic mode feedback from the central black hole. Similar conclusions have been made in previous studies of TNG both in terms of colour (Weinberger et al 2017;Nelson et al 2018a) and sSFR (Weinberger et al 2018). .…”

“…In this work, we use the IllustrisTNG simulation suite (TNG; Springel et al 2018;Marinacci et al 2018;Naiman et al 2018;Pillepich et al 2018b;Nelson et al 2018a) in order to explore this question, focusing on central galaxies with Mstar > 10 10 M . TNG uses black hole feedback in order to suppress the SFRs and Mstar content of galaxies with Mstar 10 10 M (Weinberger et al 2017(Weinberger et al , 2018. Thus, as we will show, the sSFR, Mstar, and MBH of galaxies are causally related to one another through the model's mechanism for quiescence.…”

“…In TNG, a black hole accreting in the thermal mode injects pure thermal energy into the surrounding gas particles. Weinberger et al (2018) show that the total amount of thermal energy released in this mode can be large yet has little effect on cooling and the galaxy's SFR. Thermally injected energy, as implemented for black hole thermal mode feedback in TNG, is more likely to be immediately radiated away rather than have any lasting impact on the thermodynamic properties of the gas, especially for dense gas where the cooling times are short (Navarro & White 1993;Katz et al 1996).…”

“…A popular mechanism for producing quiescence in recent physics-based galaxy formation models is black hole feedback (Bower et al 2006;Croton et al 2006;Sijacki et al 2007;Somerville et al 2008;Guo et al 2010;Booth & Schaye 2011;Vogelsberger et al 2014a;Henriques et al 2015;Somerville & Davé 2015;Schaye et al 2015;Dubois et al 2016;McCarthy et al 2017;Bower et al 2017;Weinberger et al 2018). Theoretically, accretion onto a black hole has the potential to release an enormous amount of energy into the surrounding medium.…”

“…At lower accretion rates, black holes are thought to produce jets from their accretion discs which propel lowdensity buoyant bubbles into the atmospheres of galaxies. Indeed, large extended radio-emitting lobes that create cavities within the surrounding hot gas visible in X-ray maps have been observed around massive galaxies in various environments from small groups to large clusters (e.g., Bîrzan et al 2004;McNamara & Nulsen 2007;Fabian 2012;Shin et al 2016;Werner et al 2019). Some galaxies have been observed to exhibit signs of both a bright X-ray point source in conjunction with extended radio emission, further complicating the issue of the accretion physics that could produce these varied effects on the gas within and around galaxies (Komossa et al 2006;Yuan et al 2008;Berton et al 2015;Coziol et al 2017).…”