Abstract
Feedback from super-massive black holes (SMBHs) is thought to play a key role in regulating the growth of host galaxies. Cosmological and galaxy formation simulations using smoothed particle hydrodynamics (SPH), which usually use a fixed mass for SPH particles, often employ the same sub-grid Active galactic nuclei (AGN) feedback prescription across a range of resolutions. It is thus important to ask how the impact of the simulated AGN feedback on a galaxy changes when only the numerical resolution (the SPH particle mass) changes. We present a suite of simulations modelling the interaction of an AGN outflow with the ambient turbulent and clumpy interstellar medium (ISM) in the inner part of the host galaxy at a range of mass resolutions. We find that, with other things being equal, degrading the resolution leads to feedback becoming more efficient at clearing out all gas in its path. For the simulations presented here, the difference in the mass of the gas ejected by AGN feedback varies by more than a factor of ten between our highest and lowest resolution simulations. This happens because feedback-resistant high density clumps are washed out at low effective resolutions. We also find that changes in numerical resolution lead to undesirable artifacts in how the AGN feedback affects the AGN immediate environment.
Highlights
We use a nomenclature of the form FNYZ or FMYZ, where “fixed number of neighbours (FN)” signifies that a fixed number of SMBH smoothed particle hydrodynamics (SPH) particle neighbours are heated by the feedback independently of the SPH particle number used in the simulation
“FM”, on the other hand, stands for a fixed mass of SMBH neighbour particles being heated. In these runs the number of SPH particle neighbours over which the SMBH feedback is spread depends on the numerical resolution of the simulation, and we set fBH = NSPH/104, at all resolutions
We have studied the effect of Active galactic nuclei (AGN) feedback on a multiphase interstellar medium and how such feedback is affected by numerical resolution
Summary
Feedback from AGN is often invoked in galaxy formation and cosmological simulations (e.g., Springel et al 2005; Schaye et al 2010; Dubois et al 2012; Schaye et al 2015; Vogelsberger et al 2014) as well as in semi-analytical models (e.g., Bower et al 2006; Croton et al 2006; Fanidakis et al 2012) in order to quench star formation in galaxies at the high-mass end of the mass function and reproduce a number of observational correlations such as the MBH − σ relation (Ferrarese & Merritt 2000; Gebhardt et al 2000; Tremaine et al 2002; Kormendy & Ho 2013). Outflows on kpc scales with velocities ∼> 1000 km s−1 (e.g., Cano-Dıaz et al 2012; Maiolino et al 2012; Cicone et al 2014, 2015; Tombesi et al 2015) and momentum fluxes exceeding the radiative output of the AGN, PAGN = LAGN/c, by factors of upto ∼ 30 (Dunn et al 2010; Feruglio et al 2010; Bautista et al 2010; Rupke & Veilleux 2011; Sturm et al 2011; Faucher-Giguere et al 2012; Faucher-Giguere & Quataert 2012; Genzel et al 2014; Tombesi et al 2015) have been observed and are believed to be driven by AGN Such observations provide compelling evidence that AGN can have an impact on the host galaxy, playing an important role in establishing observed correlations and vindicating the use of AGN feedback in simulations and semi-analytic models (see McNamara & Nulsen 2007; Fabian 2012; King & Pounds 2015). When radiative cooling of the wind is inefficient, it expands adiabatically and has the potential to drive the high velocity outflows discussed above and clear out significant fractions of gas from the host galaxy (Faucher-Giguere & Quataert 2012; Zubovas & King 2012)
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