The impact of radio feedback from active galactic nuclei in cosmological simulations: formation of disc galaxies

Abstract In this paper, we present a new implementation of feedback due to active galactic nuclei (AGN) in cosmological simulations of galaxy formation. We assume that a fraction of jet energy, which is generated by an AGN, is transferred to the surrounding gas as thermal energy. Combining a theoretical model of mass accretion on to black holes with a multiphase description of star-forming gas, we self-consistently follow evolution of both galaxies and their central black holes. The novelty in our model is that we consider two distinct accretion modes: standard radiatively efficient thin accretion discs and radiatively inefficient accretion flows which we will generically refer to as RIAFs; motivated by theoretical models for jet production in accretion discs, we assume that only the RIAF is responsible for the AGN feedback. The focus of this paper is to investigate the interplay between galaxies and their central black holes during the formation of a disc galaxy. We find that, after an initial episode of bursting star formation, the accretion rate on to the central black hole drops so that the accretion disc switches to a RIAF structure. At this point, the feedback from the AGN becomes efficient and slightly suppresses star formation in the galactic disc and almost completely halts star formation in the bulge. This suppression of the star formation regulates mass accretion on to the black hole and associated AGN feedback. As a result, the nucleus becomes a stochastically fuelled low-luminosity AGN (Seyfert galaxy) with recurrent short-lived episodes of activity after the star bursts. During the ‘on’ events, the AGN produces reasonably powerful jets (radio-loud state) and is less luminous than the host galaxy, while in the ‘off’ phase, the nucleus is inactive and ‘radio quiet’. Our model predicts several properties of the low-luminosity AGN including the bolometric luminosity, jet powers, the effect on kpc scale of the radio jet and the AGN lifetime, which are in broad agreement with observations of Seyfert galaxies and their radio activity. We also find that the ratios between the central black hole mass and the mass of the host spheroid at z= 0 are ∼10−3 regardless of the strength of either supernova feedback or AGN feedback because the radiation drag model directly relates the star formation activity in the Galactic Centre and the mass accretion rate on to the central black hole. black hole physics, galaxies: active, galaxies: evolution, galaxies: formation, galaxies: Seyfert, galaxies: starburst 1 INTRODUCTION Recent observations have suggested a fundamental connection between active galactic nuclei (AGN) and the formation of galaxies. First, there is now a well-established correlation between the properties of galaxies and the masses of the black holes (BH) at their centres. The mass of the central BH tightly correlates with the mass of the host galactic bulges (with a median BH-to-bulge mass ratio of ≃0.001, e.g. Kormendy & Richstone 1995; Magorrian et al. 1998; Merritt & Ferrarese 2001; McLure & Dunlop 2002; Marconi & Hunt 2003), as well as with the stellar velocity dispersion of the bulges (Ferrarese & Merritt 2000; Gebhardt et al. 2000; Tremaine et al. 2002). This discovery points to a fundamental connection between the growth of central BHs and the formation of stellar spheroids in galaxies. Secondly, high-resolution X-ray observations of galaxy clusters have revealed large, radio-plasma cavities in intracluster medium. These are usually associated with episodic outbursts from a central radio galaxy, and indicate that huge amounts of mechanical energy are being deposited into the intracluster medium by powerful AGN-driven jets (e.g. Bîrzan et al. 2004; Allen et al. 2006; Fabian et al. 2006; Rafferty et al. 2006; Taylor et al. 2006). Simulations of the impact of these AGN-driven radio cavities suggest that this powerful feedback provides sufficient energy to offset the cooling radiation from the cluster and potentially explain why so little cool (T < 3 keV) gas is seen in these systems (Quilis, Bower & Balogh 2001; Churazov et al. 2002; Dalla Vecchia et al. 2004; Omma et al. 2004; Sijacki & Springel 2006; Sijacki et al. 2007). Motivated by these discoveries, simple prescriptions for the feedback from AGN (aka. ‘radio-mode feedback’) have recently been incorporated into semi-analytic galaxy formation models (e.g. Granato et al. 2004; Cattaneo et al. 2005; Monaco & Fontanot 2005; Bower et al. 2006; Croton et al. 2006; De Lucia et al. 2006). Including radio-mode AGN feedback has resulted in dramatic improvements in the models' ability to match the sharp decline of the galaxy luminosity function and to explain the ‘down-sizing’ seen in the evolution of the galaxy population. In particular, Bower et al. show that, by assuming that AGN feedback operates only in quasi-hydrostatic haloes where the cooling time is longer than the dynamical time (Dalla Vecchia 2005; Sijacki & Springel 2006), the galaxy luminosity functions in local and higher redshifts universe can be matched well. Croton et al. (2006) and Kitzbichler & White (2007) showed that similar results were obtained by modifying the Bondi–Hoyle–Lyttleton accretion rate formula (Hoyle & Lyttleton 1939; Bondi & Hoyle 1944; Bondi 1952) to account for the multiphase structure of the accreting gas in rapidly cooling haloes. Recent simulations have also begun to track the impact of AGN feedback on the galaxy population (Di Matteo, Springel & Hernquist 2005; Kawata & Gibson 2005; Springel, Di Matteo & Hernquist 2005; Sijacki & Springel 2006; Di Matteo et al. 2007; Sijacki et al. 2007). One of the first hydrodynamic simulation of galaxy formation which invoked AGN feedback was performed by Kawata & Gibson (2005) by using cosmological simulations with smoothed particle hydrodynamics (SPH). They reproduced observed X-ray and optical properties of elliptical galaxies by injecting thermal energy into the centre of the main progenitor at z < 1, assuming that sufficient BH mass was present for the AGN to be active when a convergent gas inflow exists at the centre of the main progenitor. A self-consistent model for AGN ‘quasar-mode’ feedback associated with BH accretion in simulations of galaxy mergers was proposed by Di Matteo et al. (2005) and Springel et al. (2005). They estimated accretion rate on to BHs by using a Bondi–Hoyle–Lyttleton parametrization and injected some fraction of accreted rest mass energy into the surrounding interstellar medium (ISM) in the form of thermal energy. By using this model and performing a series of merger simulations, Hopkins et al. (2006) simulated evolution of quasar luminosity and predicted luminosity functions of quasars. In this paper, we introduce a new methodology to incorporate BH growth and AGN radio feedback self-consistently in cosmological simulations of galaxy formation. We are motivated to do this by the recent semi-analytic models that we have discussed above. Th (...truncated)