1. Cosmological evolution of Black Hole Spins Nikos Fanidakis and C. Baugh, S. Cole, C. Frenk NEB-XIII, Thessaloniki, June 4-6, 2008

2. Contents Supermassive black holes and galaxy evolution Spinning up (or down) black holes Cosmological spin evolution in hierarchical cosmologies Conclusions

3. The idea of hierarchical galaxy formation Springel et al. (2005) t=0 Gyr t=4.7 Gyr t=13.7 Gyr Initial quantum fluctuations Hierarchical cosmology Large scale structures Small scale structures mergers Lambda Cold Dark Matter (LCDM): Ω m =0.3, Ω Λ =0.7 z

4. SMBH evolution in hierarchical cosmologies Most of the massive galaxies seem to host a Supermassive Black Hole (SMBH) at their centres. (Richstone 1998) Observations suggest a rough proportionality between the black hole (BH) mass and the bulge mass. (Ferrarese & Merritt 2000; Magorrian 1998) These BH’s are treated in the standard LCDM cosmology as small BH seeds that grow through accretion and mergers. (Kauffmann & Haehnelt 2000; Malbon et al 2007) BH mergers + accretion of cold gas BH mergers + accretion of cold gas Galaxy mergers LCDM BH mass growth

5. BH formation histories Malbon et al. (2007) Fanidakis et al. (2008; in prep.)

6. Why study SMBH spins? 1.Gravitational wave source modelling 2.AGN “radio loudness” 3.Radio-jet morphology 4.SMBH spin measurements in X-ray surveys 5.Accretion efficiency Cosmological evolution of BH spins in the LCDM model Stawarz et al. (2007)

7. Mass, Spin Rotating BH’s in Astrophysics MCG -6 – 30 – 15 Fanidakis, masters thesis (2007) What do we 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 remnant BH. What will LISA observe? MCG -6 – 30 – 15 is a nearby AGN whose X-ray spectrum shows a prominent iron line at 6.4KeV. The broadness of the line indicates that

8. BH spin change in astrophysical processes BH mergers BH accretion M 1, S 1 M 2, S 2 L2L2 last stable orbit (lso) Rezzolla et al. (2007) Bardeen (1970) accretion disk

9. Spinning BH’s in LCDM: Spin evolution due to mergers Aligned mergers When the BH spins are aligned the process of BH spun up is more efficient. Isotropic mergers The BH spins have random orientation: the final BH can be spun up or spun down. Fanidakis et al. (2008; in prep.)

10. Spin distributions for different BH mass ranges (z=0) Massive BH’s (M BH ≥ 10 8 M  ) are likely to rotate rapidly. These BH’s tend to populate the centres of massive ellipticals. Fanidakis et al. (2008; in prep.)

11. BH spin distribution and merger type Galaxy mergers are divided into two categories: i. major: if M sat /M prim >0.3 ii. minor: if M sat /M prim <0.3 Galaxies that have had experienced at least one major merger are likely to dominated by rapidly rotating BH’s Fanidakis et al. (2008; in prep.)

12. Spin evolution due to mergers + accretion The accretion events in GALFORM can spin up BH’s quite efficiently. “Radio mode” accretion is not included: unclear how to model. The dominant population of maximally rotating BH’s is formed early (z=4). This population is reduced by 15% at low redshifts as a result of the BH merger events. Fanidakis et al. (2008; in prep.)

13. Spin distributions for different mass ranges BH’s with M BH ≥ 10 7 M  tend to rotate rapidly. Typical masses for the SMBH observed in AGN are M BH ≥ 10 7 M . (Marconi & Hunt 2003) The spin distributions of the massive BH populations could be relevant for indirect BH spin measurements in AGN. Fanidakis et al. (2008; in prep.)

14. Conclusions We have presented a model that deals with the evolution of BH spin in hierarchical cosmologies. In our model accretion, not binary mergers, dominate the spin distributions. BH’s in giant ellipticals that have evolved their spin only during mergers are likely to spin rapidly. Most accretion episodes produce rapidly rotating BH’s independent of the initial spin.