Cosmological simulations of the growth of supermassive black holes and feedback from active galactic nuclei: method and tests

Abstract

We present a method that self‐consistently tracks the growth of supermassive black holes (BHs) and the feedback from active galactic nuclei (AGN) in cosmological, hydrodynamical simulations. Our model is a substantially modified version of the one introduced by Springel, Di Matteo & Hernquist implemented in a significantly expanded version of the gadget III code, which contains new prescriptions for star formation, supernova feedback, radiative cooling and chemodynamics. We simulate the growth of BHs from an initial seed state via Eddington‐limited accretion of the surrounding gas, and via mergers with other BHs. Because cosmological simulations at present lack both the resolution and the physics to model the multiphase interstellar medium, they tend to strongly underestimate the Bondi–Hoyle accretion rate. To allow low‐mass BHs to grow, it is therefore necessary to increase the predicted Bondi–Hoyle rates in star‐forming gas by large factors, either by explicitly multiplying the accretion rate by a numerical correction factor or by using an unresolved, subgrid model for the gas close to the BH. We explore the physical regimes where the use of such multiplicative factors is reasonable, and through this introduce a new prescription for gas accretion by BHs. Feedback from AGN is modelled by coupling a fraction of the rest‐mass energy of the accreted gas thermally into the surrounding medium. We describe the implementation as well as the limitations of the model in detail and motivate all the changes relative to previous work. We demonstrate how general physical considerations can be used to choose many of the parameters of the model and demonstrate that the fiducial model reproduces observational constraints. We employ a large suite of cosmological simulations, in which the parameters of the BH model are varied away from their fiducial values, to investigate the robustness of the predictions for the cosmic star formation history and the redshift zero cosmic BH density, BH scaling relations and galaxy‐specific star formation rates. We find that the freedom introduced by the need to increase the predicted accretion rates by hand, the standard procedure in the literature, is the most significant source of uncertainty. Our simulations demonstrate that supermassive BHs are able to regulate their growth by releasing a fixed amount of energy for a given halo mass, independent of the assumed efficiency of AGN feedback, which sets the normalization of the BH scaling relations. Regardless of whether BH seeds are initially placed above or below the BH scaling relations, they grow on to the same scaling relations. AGN feedback efficiently suppresses star formation in high‐mass galaxies.

Cosmic discordance: are Planck CMB and CFHTLenS weak lensing measurements out of tune?

“…CFHTLenS σ 8 constraints in an otherwise fixed fiducial cosmology, with 3 different nonlinear power spectrum treatments. Also shown is the constraint using TA12 and a prescription for AGN feedback described in Section 3.3 model, which accounts for the presence of black holes and AGN feedback in dark matter halos using the prescription described in Booth & Schaye (2009), is the most realistic of the different OWLS models, since it matches well both the observed optical and X-ray properties of galaxy groups (McCarthy et al (2011)). To test the effect of AGN feedback on the CFHTLenS constraints, we use the matter power spectra 3 derived by van Daalen et al (2011) from the OWLS.…”

Spatially adaptive radiation-hydrodynamical simulations of galaxy formation during cosmological reionization

“…The comparison with the small and large box simulations L12N256 and L50N512 supports box size as a limiting factor in accurate determinations of the SFR function at the highest SFRs. Additional processes that may impact models of the SFR function at high SFRs include feedback from massive black holes (e.g., Di Matteo, Springel, & Hernquist 2005;Booth & Schaye 2009), which we have ignored here, and obscuration by dust (e.g., Cai et al 2014). While we compare to observations of dust-corrected SFRs, there are large systematic uncertainties in the amount of dust as well as its properties, especially at the high redshifts of interest here (e.g., Smit et al 2012;Duncan et al 2014).…”

Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge

“…However, like other simulations, the current simulations are not yet doing the most accurate possible job in treating the star formation and feedback processes. For example, the code used here assumes a somewhat high SFR efficiency per free-fall time, it does not follow in detail the formation of molecules and the effect of metallicity on SFR (Krumholz & Dekel 2012), and it does not explicitly include radiative stellar feedback (Murray et al 2010;Krumholz & Dekel 2010;Hopkins et al 2012;Dekel & Krumholz 2013) or AGN feedback (Silk & Rees 1998;Hopkins et al 2006;Ciotti & Ostriker 2007;Booth & Schaye 2009;Cattaneo et al 2009;Fabian 2012;DeGraf et al 2014). Therefore, the early SFR is overestimated, while the suppression of SFR in small galaxies is underestimated, resulting in excessive early star formation prior to z ∼ 3, by a factor of order 2.…”