1. Image from ESO Black Hole Fueling

2. Accretion to Supermassive Black Hole 10^6Mo 10^8 yr a: Ho, Filippenko & Sargent 1997a

3. Angular Momentum Problem • Specific angular momentum of matter at r=10kpc to the last stable orbit: 100,000:1 • At 200pc, L is still a factor of 1000 too large… What mechanisms drive gas clouds from kpc to subpc? • Gravitational Torque (by Bars) • Dynamical Friction • Viscous Torque

4. Dominant Fueling Mechanism(large to intermediate scale: 10kpc -> 1kpc) Bar exerts torque on gas clouds at large radii (~few kpc) Due to their collisional and dissipative nature, **Clouds lose L gradually and can be driven by the bar potential to few-hundred pc

5. Stars and gas in a barred potential Figures from Buta & Combes 1996 Illustration Credit: Frattare (STScI)

6. Yea! Way to go, our gas cloud Outer ILR Inner ILR

7. What happen to our gas cloud!? • Gas-populated orbits change their orientation only gradually due to shocks • When clouds reach OILR, the negative torque exert on the cloud cause it to lose significant L • Radial inflow slows as gas cross IILR… • Gas are trapped in the IILR in a form of ring

8. CO concentration Jogee at al. 2004c Barred (Large scale) Galaxies - High concentration of CO and H alpha at the centers of the starburst galaxies - Relatively low concentration at the center for non-starbursts - See a “ring” of gas surrounding the center of galaxy

9. Surface density is derived from the CO (J=1-0) Jogee at al. 2004c Non-Starbursts: - “Ring” located at the peak of the curve? - Gas surface density increases, stop rising then drop Starbursts: - Gas surface density keep rising A higher resolution is need to probe the gas in the inner 100pc region…

10. Relation btw Large-scale bars and starburst Statistical Studies of 12um (Seyfert) Galaxies Hunt & Malkan 1999 SB+SAB SAB Compared to Extended 12um Sample (E12GS) unbarred Overall: Fraction of large-scale bar (SB+SAB) is larger in starbursts (82-85%) than in the normal (61-68%) ones Data Bins: S0a and earlier (T≤ 0); Sa, Sab (0< T≤ 2); Sb, Sbc (2< T≤ 4); Sc, Scd (4< T≤ 6); Sdand later (6< T)

11. Barred Galaxy = AGN?? • Galaxies with LS-Bar are more likely to harbor AGN • Yet, theory suggest LS-Bar can only drive gas to r=100s pc • For AGN, there must be some other mechanisms to drive gas from few 100s to sub-pc • Thus, we DO NOT expect all barred galaxies to show AGN activity

12. The journey from few-100s to tens pc • If Ωn≠Ωp, bar decoupling happens • Secondary/Nuclear Bar (200-1600pc) exerts a negative torque • Counterclockwise rotation of the nuclear bar is a possible outcome of Merger! • Simulations: decouple phase with Ωn>Ωp can remove L effectively

13. Example of nuclear stellar bar feeding Jogee, Kenney, & Smith 1999

14. More recent example (NUGA) Garcia-Burillo et al. 2005

15. Nuclear Bars = AGN? • Theoretically, nuclear bar help to solve the L problem one step further, to few tens pc • NOT ALL nuclear bars are expected to be effective in removing L (depends on the pattern speeds) • Alternative: SN, Cloud-Cloud collision?

16. Final destination to SMBH • At 100pc, L is still 100 times too large to get into subpc scales • Dynamical friction becomes important • As the gas cloud loses momentum, SMBH dominates the potential • Cloud being tidal disrupted, forming a disk around the SMBH • Viscous Torque kicks in

17. Different time scales for an infalling 1e7 solar-mass cloud DF time scale becomes effective as the gas cloud reaches 100s pc scales Jogee et al. 1999

18. Tidal disruption of Giant Cloud => L redistribution BEKKI 2000 N=5000

19. Accreting Mass into MBH MBH is in unit of 10^7 solar mass (same as the mass of cloud) Significant amount of gas fit into a lower angular momentum orbit Few percent of gas in the clump is found to be transferred in to subpc region What else are important for feeding in a sub-pc region? Magnetic Field

20. Baby N-body simulation N = 100 T=1.5Myr T=0 T=1Myr T=2.5Myr T=3Myr T=2Myr

21. Q & A + Thanks