A new twist on black holes: the role of black hole spin in galaxy formation.

We study the coevolution of black holes (BHs) and their host galaxies through cosmic time. The calculation is embedded in the GALFORM semi-analytic model which simulates the formation and evolution of galaxies in a cold dark matter (CDM) universe. The BH and galaxy formation models are coupled: during the evolution of the host galaxy, hot and cold gas are added to the BH by flows triggered by halo gas cooling, disc instabilities and galaxy mergers. This builds up the mass and spin of the BH, and the resulting accretion power regulates gas cooling and subsequent star formation. Using the Blandford–Znajek mechanism for jet production to calculate the jet power, our model reproduces the radio loudness of radio galaxies, LINERS and Seyferts, suggesting that the jet properties of active galactic nuclei (AGN) are a natural consequence of both the accretion rate onto and the spin of the central BH. The model also reproduces the observed luminosity functions (LF) of AGN (optical, soft and hard X-ray, and bolometric) for a wide range of redshifts (0 < z < 6). We find downsizing in the AGN population, in terms of the differential growth with redshift of the space density of faint and bright AGN. This arises naturally from the interplay between the different accretion channels that drive the growth of BHs. The predictions of our model are extended to 6 < z < 20 to study the early growth of BHs. Our model predicts that the first 10^{8} M⊙ BHs appear at z = 14, along with the first luminous quasars. Finally, we explore the dependence of AGN activity and luminosity on environment. We find that quasars inhabit haloes with masses 10^{12} − 10^{13} M⊙. Quasar activity in more massive haloes in suppressed due to AGN feedback. In contrast, radio galaxies occupy the centres of the most massive haloes. Our model represents the first consistent demonstration that the phenomenology and evolution of AGN can be naturally explained by the coeval evolution of galaxies and BHs, coupled by AGN feedback, in a CDM universe

The spatial clustering of ROSAT All-Sky Survey Active Galactic Nuclei IV. More massive black holes reside in more massive dark matter halos

This is the fourth paper in a series that reports on our investigation of the clustering properties of active galactic nuclei (AGN) identified in the ROSAT All-Sky Survey (RASS) and Sloan Digital Sky Survey (SDSS). In this paper we investigate the cause of the X-ray luminosity dependence of the clustering of broad-line, luminous AGN at 0.16<z<0.36. We fit the H-alpha line profile in the SDSS spectra for all X-ray and optically-selected broad-line AGN, determine the mass of the super-massive black hole (SMBH), M_BH, and infer the accretion rate relative to Eddington (L/L_EDD). Since M_BH and L/L_EDD are correlated, we create AGN subsamples in one parameter while maintaining the same distribution in the other parameter. In both the X-ray and optically-selected AGN samples we detect a weak clustering dependence with M_BH and no statistically significant dependence on L/L_EDD. We find a difference of up to 2.7sigma when comparing the objects that belong to the 30% least and 30% most massive M_BH subsamples, in that luminous broad-line AGN with more massive black holes reside in more massive parent dark matter halos at these redshifts. These results provide evidence that higher accretion rates in AGN do not necessarily require dense galaxy environments in which more galaxy mergers and interactions are expected to channel large amounts of gas onto the SMBH. We also present semi-analytic models which predict a positive M_DMH dependence on M_BH, which is most prominent at M_BH ~ 10^{8-9} M_SUN.Comment: 24 pages, 16 figures, 2015 ApJ, 815, 2

Investigating evidence for different black hole accretion modes since redshift z~1

Chandra data in the COSMOS, AEGIS-XD and 4Ms CDFS are combined with optical/near-IR photometry to determine the rest-frame U-V vs V-J colours of X-ray AGN hosts at mean redshifts 0.40 and 0.85. This combination of colours (UVJ) provides an efficient means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasises differences between AGN split by their UVJ colours. AGN in quiescent galaxies are dominated by spheroids, while star-forming hosts are split between bulges and disks. The UVJ diagram of AGN hosts is then used to set limits on the accretion density associated with evolved and star-forming systems. Most of the black hole growth since z~1 is associated with star-forming hosts. Nevertheless, ~15-20% of the X-ray luminosity density since z~1, is taking place in the quiescent region of the UVJ diagram. For the z~0.40 subsample, there is tentative evidence (2sigma significance), that AGN split by their UVJ colours differ in Eddington ratio. AGN in star-forming hosts dominate at high Eddington ratios, while AGN in quiescent hosts become increasingly important as a fraction of the total population toward low Eddington ratios. At higher redshift, z~0.8, such differences are significant at the 2sigma level only at Eddington ratios >1e-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of SMBHs at the centres of galaxies. We compare our results with the GALFORM semi-analytic model, which postulates two black hole fuelling modes, the first linked to star-formation and the second occuring in passive galaxies. GALFORM predicts a larger fraction of black hole growth in quiescent galaxies at z<1, compared to the data. Relaxing the strong assumption of the model that passive AGN hosts have zero star-formation rate could reconcile this disagreement.Comment: MNRAS accepte

The environment of radio galaxies: a signature of AGN feedback at high redshifts

We use the semi-analytical model of galaxy formation GALFORM to characterize an indirect signature of active galactic nucleus (AGN) feedback in the environment of radio galaxies at high redshifts. The predicted environment of radio galaxies is denser than that of radio-quiet galaxies with the same stellar mass. This is consistent with observational results from the CARLA survey. Our model shows that the differences in environment are due to radio galaxies being hosted by dark matter haloes that are ∼1.5 dex more massive than those hosting radio-quiet galaxies with the same stellar mass. By running a control simulation in which AGN feedback is switched off, we identify AGN feedback as the primary mechanism affecting the build up of the stellar component of radio galaxies, thus explaining the different environment in radio galaxies and their radio-quiet counterparts. The difference in host halo mass between radio-loud and radio-quiet galaxies translates into different galaxies populating each environment. We predict a higher fraction of passive galaxies around radio-loud galaxies compared to their radio-quiet counterparts. Furthermore, such a high fraction of passive galaxies shapes the predicted infrared luminosity function in the environment of radio galaxies in a way that is consistent with observational findings. Our results suggest that the impact of AGN feedback at high redshifts and environmental mechanisms affecting galaxies in high halo masses can be revealed by studying the environment of radio galaxies, thus providing new constraints on galaxy formation physics at high redshifts

Cosmological Evolution of Supermassive Black Holes. II. Evidence for Downsizing of Spin Evolution

The spin is an important but poorly constrained parameter for describing supermassive black holes (SMBHs). Using the continuity equation of SMBH number density, we explicitly obtain the mass-dependent cosmological evolution of the radiative efficiency for accretion, which serves as a proxy for SMBH spin. Our calculations make use of the SMBH mass function of active and inactive galaxies (derived in the first paper of this series), the bolometric luminosity function of active galactic nuclei (AGNs), corrected for the contribution from Compton-thick sources, and the observed Eddington ratio distribution. We find that the radiative efficiency generally increases with increasing black hole mass at high redshifts (z>~1), roughly as \eta \propto M_bh^0.5, while the trend reverses at lower redshifts, such that the highest efficiencies are attained by the lowest mass black holes. Black holes with M_bh>~10^8.5M_sun maintain radiative efficiencies as high as \eta~0.3-0.4 at high redshifts, near the maximum for rapidly spinning systems, but their efficiencies drop dramatically (by an order of magnitude) by z~0. The pattern for lower mass holes is somewhat more complicated but qualitatively similar. Assuming that the standard accretion disk model applies, we suggest that the accretion history of SMBHs and their accompanying spins evolve in two distinct regimes: an early phase of prolonged accretion, plausibly driven by major mergers, during which the black hole spins up, then switching to a period of random, episodic accretion, governed by minor mergers and internal secular processes, during which the hole spins down. The transition epoch depends on mass, mirroring other evidence for "cosmic downsizing" in the AGN population; it occurs at z~2 for high-mass black holes, and somewhat later, at z~1, for lower-mass systems.Comment: To appear in the ApJ, 11 pages and 9 figure

Accretion, Growth of Supermassive Black Holes, and Feedback in Galaxy Mergers

Super-Eddington accretion is very efficient in growing the mass of a black hole: in a fraction of the Eddington time its mass can grow to an arbitrary large value if the feedback effect is not taken into account. However, since super-Eddington accretion has a very low radiation efficiency, people have argued against it as a major process for the growth of the black holes in quasars since observations have constrained the average accretion efficiency of the black holes in quasars to be \ga 0.1. In this paper we show that the observational constraint does not need to be violated if the black holes in quasars have undergone a two-phase growing process: with a short super-Eddington accretion process they get their masses inflated by a very large factor until the feedback process becomes important, then with a prolonged sub-Eddington accretion process they have their masses increased by a factor \ga 2. The overall average efficiency of this two-phase process is then \ga 0.1, and the existence of black holes of $10^9 M_\odot$ by redshift 6 is easily explained. Observational test of the existence of the super-Eddington accretion phase is briefly discussed.Comment: 11 pages, 4 figures. Submitted to MNRA

Investigating Evidence for Different Black Hole Accretion Modes since Redshift \u3cem\u3ez\u3c/em\u3e ∼ 1

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U − V versus V − J colours of X-ray AGN hosts in the redshift intervals 0.1 \u3c z \u3c 0.6 (mean z¯=0.40) and 0.6 \u3c z \u3c 1.2 (mean z¯=0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by theirU − V versus V − J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U − V versusV − J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z ≈ 0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15–20 per cent, at both z¯=0.40 and 0.85, is taking place in galaxies in the quiescent region of the U − V versus V − J diagram. For the low-redshift sub-sample, 0.1 \u3c z \u3c 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U − V and V − J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift, z \u3e 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≳ 10− 3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies. We compare these results with the predictions of theGALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z \u3c 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data

The clustering of X-ray selected AGN at z=0.1

The clustering properties of moderate luminosity ($L_X = \rm 10^{41} - 10^{44} \, erg \,s^{-1}$) X-ray selected AGN at $z\approx0.1$ are explored. X-ray sources in the redshift interval $0.03<z<0.2$ are selected from a serendipitous XMM survey of the SDSS footprint (XMM/SDSS) and are cross-correlated with the SDSS Main galaxy sample. The inferred X-ray AGN auto-correlation function is described by a power law with amplitude $r_0\approx5\,$h$^{-1}$Mpc and slope $\gamma\approx2.0$. The corresponding mass of the dark matter haloes that host X-ray AGN at $z\approx0.1$ is \approx 10^{13} \,h ^{-1} \, M_{\sun}. Comparison with studies at higher redshift shows that this mass scale is characteristic of moderate luminosity X-ray AGN out to $z\approx 1$. Splitting the AGN sample by rest-frame color shows that X-ray sources in red hosts are more clustered than those associated with blue galaxies, in agreement with results at $z\approx1$. We also find that the host galaxies of X-ray AGN have lower stellar masses compared to the typical central galaxy of a \approx 10^{13} \,h ^{-1} \, M_{\sun} dark matter halo. AGN hosts either have experienced less stellar mass growth compared to the average central galaxy of a \approx 10^{13} \,h ^{-1} \, M_{\sun} halo or a fraction of them are associated with satellite galaxies.Comment: MNRAS accepted 14 pages, 8 figures, 5 table