The deposition of mechanical feedback from a supermassive black hole (SMBH) in an active galactic nucleus (AGN) into the surrounding galaxy occurs via broad-line winds which must carry mass and radial momentum as well as energy. The effect can be summarized by the dimensionless parameteris the efficiency by which accreted matter is turned into wind energy in the disc surrounding the central SMBH. The outflowing mass and momentum are proportional to η, and many prior treatments have essentially assumed that η = 0. We perform one-and two-dimensional simulations and find that the growth of the central SMBH is very sensitive to the inclusion of the mass and momentum driving but is insensitive to the assumed mechanical efficiency. For example in representative calculations, the omission of momentum and mass feedback leads to an hundred fold increase in the mass of the SMBH to over 10 10 M ⊙ . When allowance is made for momentum driving, the final SMBH mass is much lower and the wind efficiencies which lead to the most observationally acceptable results are relatively low with ǫ w 10 −4 .

We study the growth of black holes (BHs) in galaxies using three-dimensional smoothed particle hydrodynamic simulations with new implementations of the momentum mechanical feedback, and restriction of accreted elements to those that are gravitationally bound to the BH. We also include the feedback from the X-ray radiation emitted by the BH, which heats the surrounding gas in the host galaxies, and adds radial momentum to the fluid. We perform simulations of isolated galaxies and merging galaxies and test various feedback models with the new treatment of the Bondi radius criterion. We find that overall the BH growth is similar to what has been obtained by earlier workers using the Springel, Di Matteo, & Hernquist algorithms. However, the outflowing wind velocities and mechanical energy emitted by winds are considerably higher (v w ∼ 1000 − 3000 km s −1 ) compared to the standard thermal feedback model (v w ∼ 50 − 100 km s −1 ). While the thermal feedback model emits only 0.1% of BH released energy in winds, the momentum feedback model emits more than 30% of the total energy released by the BH in winds. In the momentum feedback model, the degree of fluctuation in both radiant and wind output is considerably larger than in the standard treatments. We check that the new model of the BH mass accretion agrees with analytic results for the standard Bondi problem.

We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of M stel = 8.8 × 10 10 − 6.0 × 10 11 M ⊙ . Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 halos with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter halos and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M BH − σ relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of two compared to models without any AGN feedback at all halo masses. However, massive galaxies simulated with thermal AGN feedback show a factor of ∼ 10 − 100 higher X-ray luminosities than observed. The mechanical/radiation feedback model reproduces the observed correlation between X-ray luminosities and velocity dispersion, e.g. for galaxies with σ = 200 km s −1 , the X-ray luminosity is reduced from 10 42 erg s −1 to 10 40 erg s −1 . It also efficiently suppresses late time star formation, reducing the specific star formation rate from 10 −10.5 yr −1 to 10 −14 yr −1 on average and resulting in quiescent galaxies since z=2, whereas the thermal feedback model shows higher late time in-situ star formation rates than observed.

We ask how the inclusion of various physical heating processes due to the metal content of gas affect the evolution of central massive galaxies and compute a suite of cosmological hydrodynamical simulations that follow these systems and their supermassive black holes. We use a smoothed particle hydrodynamics code with a pressure-entropy formulation and a more accurate treatment of the metal production, turbulent diffusion and cooling rate based on individual element abundances. The feedback models include (1) AGN feedback via high velocity broad absorption line winds and Compton/photoionization heating, (2) explicit stellar feedback from multiple processes including powerful winds from supernova events, stellar winds from young massive stars and AGB stars as well as radiative heating within Strömgren spheres around massive stars, and (3) additional heating effects due to the presence of metals including grain photoelectric heating, metallicity dependent X-ray heating by nearby accreting black holes and from the cosmic X-ray background, which are the major improvements in our feedback model. With a suite of zoom-in simulations of 30 halos with M vir ∼ 10 12.0−13.4 , we show that energy and momentum budgeted from all feedback effects generate realistic galaxy properties. We explore the detailed role of each feedback model with three additional sets of simulations with varying input physics. We show that the metal induced heating mechanisms reduce the fraction of accreted stellar material by mainly suppressing the growth of diffuse small stellar systems at high redshift but overall have a relatively minor effect on the final stellar and gas properties of massive central galaxies. The inclusion of AGN feedback significantly improves the ability of our cosmological hydrodynamical simulations to yield realistic gas and stellar properties of massive galaxies with a reasonable fraction of the final stellar mass which is accreted from other galaxies.

Galaxies occupy different regions of the [O iii]λ5007/Hβ-versus-[N ii]λ6584/Hα emission-line ratio diagram in the distant and local Universe. We investigate the origin of this intriguing result by modelling self-consistently, for the first time, nebular emission from young stars, accreting black holes (BHs) and older, post-asymptoticgiant-branch (post-AGB) stellar populations in galaxy formation simulations in a full cosmological context. In post-processing, we couple new-generation nebular-emission models with high-resolution, cosmological zoom-in simulations of massive galaxies to explore which galaxy physical properties drive the redshift evolution of the opticalline ratios [O iii]λ5007/Hβ, [N ii]λ6584/Hα, [S ii]λλ6717, 6731/Hα and [O i]λ6300/Hα. The line ratios of simulated galaxies agree well with observations of both star-forming and active local SDSS galaxies. Toward higher redshifts, at fixed galaxy stellar mass, the average [O iii]/Hβ is predicted to increase and [N ii]/Hα, [S ii]/Hα and [O i]/Hα to decrease -widely consistent with observations. At fixed stellar mass, we identify star formation history, which controls nebular emission from young stars via the ionization parameter, as the primary driver of the cosmic evolution of [O iii]/Hβ and [N ii]/Hα. For [S ii]/Hα and [O i]/Hα, this applies only to redshifts greater than z = 1.5, the evolution at lower redshift being driven in roughly equal parts by nebular emission from active galactic nuclei and post-AGB stellar populations. Instead, changes in the hardness of ionizing radiation, ionized-gas density, the prevalence of BH accretion relative to star formation and the dust-to-metal mass ratio (whose impact on the gas-phase N/O ratio we model at fixed O/H) play at most a minor role in the cosmic evolution of simulated galaxy line ratios.