On the nature of AGN in hierarchical galaxy formation models

1. On the nature of AGN in hierarchical galaxy formation models Nikos Fanidakis and C.M. Baugh, R.G. Bower, S. Cole, C. Done, C. S. Frenk Leicester, March 6, 2009

2. Outline • Hierarchical galaxy formation • Supermassive black hole (SMBH) growth in hierarchical cosmologies • Cosmological black hole (BH) spin evolution • Predicting the radio loudness of active galactic nuclei (AGN) • Conclusions

3. The idea of hierarchical galaxy formation t=13.7 Gyr Hierarchical cosmology Initial quantum fluctuations t=4.7 Gyr gravity Small-scale structure formation Springel et al. (2005) mergers t=0 Gyr Large scale structures z

4. The GALFORM semi-analytical model • GALFORM • Dark matter haloes • Merger trees from Millennium simulation • Galaxy formation • Semi-analytic models for: • Gas cooling • Star formation • Feedback processes • Chemical evolution • Galaxy mergers • Galaxy sizes • SMBH evolution • etc. Why semi-analytics? • Direct N-body simulations have limited dynamical range. • Semi-analytical approach: use of analytical prescriptions for modeling different physical processes.

5. Rotating SMBHs in astrophysics Facts Mass, Spin • BHs are the simplest objects in the Universe. • They can be completely described by just two parameters, the mass and the spin. • Each galaxy is believed to host a BH at its centre with a mass of 106-109M.

6. Rotating SMBHs in astrophysics What do we observe? MCG -6 – 30 – 15 is a nearby Seyfert galaxy whose X-ray spectrum shows a prominent iron line at 6.4KeV. The emission is believed to originate at ~2rschw, indicating: NF, masters thesis (2007) MCG -6 – 30 – 15 Energy (keV) What will LISA observe? The gravitational wave detector LISA (to be launched in 2018) is expected to directly observe mergers of SMBH binaries and precisely measure the spin of the final BH remnant.

7. How do we model SMBHs in hierarchical cosmologies? Host galaxies SMBHs Disk - Progenitor haloes - Each disk hosts a SMBH - DM haloes merge - DM haloes merge Hot gas - Satellite galaxy sinks towards the central galaxy through dynamical friction - Major merger • - Satellite SMBH sinks • towards the central SMBH • through dynamical friction • BH binary forms – emission of GW • - Binary merger - Starburst (quasar mode) and spheroid formation - Vast amounts of gas are being accreted onto the SMBH - Accretion of hot gas (radio mode) forms new disk - Quiescent accretion of gas from the hot halo onto the SMBH

8. The growth of SMBHs mass • Co-evolution of SMBHs and host spheroids leads to a BH mass-bulge relation. • Channels of SMBH growth: • Cold gas accretion: accretion of gas during galaxy mergers and disk instabilities. • Hot gas accretion: quiescent accretion from hot halo. • BH binary mergers. • The growth of mass affects the evolution of the BH spin.

9. The growth of SMBHs mass • Co-evolution of SMBHs and host spheroids leads to a BH mass-bulge relation. • Channels of SMBH growth: • Cold gas accretion: accretion of gas during galaxy mergers and disk instabilities. • Hot gas accretion: quiescent accretion from hot halo. • BH binary mergers. • The growth of mass affects the evolution of the BH spin.

10. BH spin change due to accretion • Gas accreted via an accretion disk transfers its angular momentum at the last stable orbit to the BH: • Co-rotating gas – spin up • Counter-rotating gas – spin down BH Bardeen (1970) • The size of the disk is limited by its self gravity. • If the disk does not lie on the equatorial plane of the BH Lense-Thirring precession will (anti-) align the disk. • Alignment occurs if: last stable orbit (lso) accretion disk King etal. (2005)

11. BH spin change due to binary mergers • Binary BHs form during galaxy mergers. • The system hardens due to the emission of gravitational waves. • During the merger the satellite BH transfers its angular momentum and spin to the central BH. • The final remnant is always a rotating BH. L2 M2, S2 M1, S1 BH binary evolution in numerical relativity Rezzolla et al. (2007)

12. Evolution of SMBH spins in hierarchical cosmologies Evolution of spin with redshift Distributions in different mass bins

13. AGN Jets • Jet formation: • Twisted magnetic lines collimate outflows of plasma. • The jet removes energy from the disk/BH. • The plasma trapped in the lines accelerates and produces large-scale flows. • The jet power increases proportionally to the BH spin: Image source: Narayan+05 Blandford & Znajek 1977 M87

14. AGN radio loudness dichotomy AGN radio loudness: Observational facts • AGN can be divided into two classes: • Radio-loud objects (strong jets) • Radio-quiet objects (no jets) • AGN form two distinct sequences on the Lbol –Lradio plane: • Upper sequence: objects hosted by giant ellipticals with MSMBH>108M • Lower sequence: objects hosted by ellipticals and spirals with MSMBH<108M • Spin paradigm: the BH spin is believed to determine the radio loudness of an AGN Data: Sikora et al. 2007

15. AGN in GALFORM: modelling the disk/jet Accretion in GALFORM spans a wide range of accretion rates: Note: The geometry of the disk depends on the accretion rate! Remember: Thin disk Meier 1999 ADAF

16. AGN radio loudness: theoretical predictions

17. AGN radio loudness: theoretical predictions

18. A unified models for the radio loudness of AGN?

19. Conclusions • We have developed a model using GALFORM for explaining the radio loudness of AGN in hierarchical cosmological models. • We find that in the present universe SMBHs have a bimodal distribution of spins. • Giant ellipticals are found to host massive SMBHs (MBH>108Msun) that rotate rapidly. • Using the Blandford-Znajek mechanism we model the radio emission from AGN. Our results are in good agreement with the observations. • In our model the radio properties of an AGN seem to be determined by the spin and accretion rate characterising the central SMBH.

20. Quasar LF