Impact of AGN feedback on galaxies and their multiphase ISM across cosmic time

Abstract

We present simulations of galaxy formation, based on the GADGET-3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for AGN feedback. Our sub-resolution model describes a multiphase ISM, accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies (M halo, DM 2 · 10 12 M , at z = 0), to investigate: (i) the effect of different ways of coupling AGN feedback energy to the multiphase ISM; (ii) the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); (iii) how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive BHs and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at z = 0 is reduced by up to an order of magnitude, and the BH is prevented from accreting below z 2, when the galaxy disc forms.

The importance of black hole repositioning for galaxy formation simulations

“…in runs that varied the coupling between angular momentum and the suppression factor (their fig. 11;Valentini et al 2020 report similar results for their independent implementation). Suitable changes to other subgrid parameters can compensate for this difference and lead to realistic star formation histories with a standard Bondi-Hoyle-Lyttleton accretion formula.…”

A universal relation between the properties of supermassive black holes, galaxies, and dark matter halos

“…'quasar'-mode and 'radio'-mode) depending on the BH accretion rate. Also, 𝜖 f varies significantly from one model to another: for instance, in their hydrodynamical simulations, Valentini et al (2020) implemented the coupling between the AGN energy and a realistic multi-phase ISM, finding that 𝜖 f ∼ 10 −2 adequately regulates the BH growth in Milky Way-like galaxies. A simplification that we adopted here is the absence of an AGN duty cycle: our model assumes a continuous feeding for the BH, corresponding to a continuous energy output distributed over the entire galaxy lifespan, whereas the observed AGN activity is intermittent.…”

Host galaxies of high-redshift quasars: supermassive black hole growth and feedback

“…The sub-resolution model that we adopt for our cosmological simulations is MUPPI (MUlti Phase Particle Integrator): it represents a multiphase ISM and accounts for a variety of physical processes which occur on scales not explicitly resolved. The model has been introduced and thoroughly described in Murante et al (2010Murante et al ( , 2015 and Valentini et al (2017Valentini et al ( , 2019Valentini et al ( , 2020: in this Section, we outline its main features, while we refer the reader to the aformentioned papers for a more comprehensive discussion and any further details.…”

“…Wind particles receiving energy use it to increase their velocity along their least resistance path, since they are kicked against their own density gradient. We refer the interested reader to the aforementioned papers (Murante et al 2010(Murante et al , 2015Valentini et al 2017Valentini et al , 2019 for a thorough description of all the processes included in our sub-resolution model; in particular, Section 2 of Valentini et al (2020) provides a comprehensive summary and can be taken as a reference for the values of all the parameters not explicitly mentioned here. A gas particle exits the multiphase stage when its density drops below a density threshold (0.2𝜌 thresh ) or once a maximum time (set by the dynamical time of the cold gas) elapses.…”