1. Molecular gas flows in galaxies Françoise Combes Garching, 10 September 2007 Outline: Observational evidence Angular momentum transfers Bar destruction, role of gas, of DM AGN fueling, torques & NUGA

2. 2 Gas concentrations (CO emission) Sakamoto et al 1999, Sheth et al 2005 (BIMA-SONG) Sheth et al, 2005 Barred spirals have higher molecular concentration in the central kpc Bars induce gas flows M tot M nuc

3. 3 Evidence of molecular gas flows PAH as tracer of SFR (Spitzer) Star formation is more spectacular in the center of pseudo-bulges (< 1.5kpc) (Fisher 2006) Regan et al 2006: Large central 8 +CO emission Related to secular evolution PAH emission pseudo-bulge No 8 concentration classical bulge SINGS (Spitzer) N7331 N3627 N3351

4. 4 Formation of rings Resonant rings (ILR, UHR, OLR), where gas is piling up Trace of gravity torques N1068 (BIMA) IRAM (Schinnerer et al 2000) NUGA N7217 N6951 N3147

5. 5 Angular Momentum transfers The gas loses its AM through gravity torques Viscous torques are in general negligible (Bournaud et al 05) AM transfer from baryons to DM (Athanassoula 2002, 2003) If DM dominated disk, without gas AM is exchanged with the outer disk and gas, if not DM dominated

6. 6 Bar gravity torques concentrate mass towards the center Rate quantified by observations Computations of the torque from the red image, on the gas distribution (H ) Action on the gas: sign of the torques, depending on the phase shift between gas and stellar potential NGC 7479

7. 7 DEC Gas at large scale? 2 patterns OLR of the 1st = ILR of the 2nd

8. 8 Bar destruction by gas Gas is driven in by the bar torques The angular momentum is taken up by the bar wave fgas=6% With negligible DM No gas A RC A SF Bar strength time This destroys the bar negative momentum inside CR Not only the presence of the Central Mass Concentration Effect of gas depends on the cooling: Isothermal (RC) or adiabatic (A) Debattista et al (2006)

9. 9 History of gas flows and accretion Heller, Shlosman & Athanassoula 2007 Bars form, destroy and reform Gas accretes by intermittence First it is confined outside OLR until the bar weakens, then it can replenish the disk, to make it unstable again to bar formation

10. 10 Low importance of AM transfers with gas Berentzen et al 2007 Transfer to DM more important (fgas < 8%) However, bar destroys more quickly with gas Interpreted as a function of destruction of vertical resonance Help of the CMC Fgas should be higher In presence of massiveDM * -DM *-gas

11. 11 Gas flows and AGN/SB feedback Bar torques gas inflow inside CR bar destruction gas inflow from OLR & inside ILR At each cycle, Starburst in nuclear rings, AGN fueling NUGA observations: The AGN fueling phase is very short CR

12. 12 N6951: potential from red image CO in ILR ring Strength of the bar Q 2 = F tan /F rad

13. 13 Torques computation Garcia-Burillo et al 2005

14. 14 N2782 nuclear disk + outflow Jogee et al 1999

15. 15 N2782: CO in the nuclear bar Hunt et al 2007

16. 16 NGC 2782: torques Torques are here systematically negative Due to a secondary bar

17. 17 N2782: model Stars Gas Zoom Formation of a primary bar and decoupled 2nd bar in N-body+ hydro simulation Short phase, when torques are negative down to the very center

18. 18 Nested bars in N2782 The CR of the nuclear bar Is the ILR of the primary bar Hunt et al 2007

19. 19 N6574: CO and NIR J-H from Kotilainen et al 2000 J and CO CO in UHR ring and bar

20. 20 NGC 6574: torques Qm Phases Torque map Lindt-Krieg et al 2007

21. 21 N3147: torques Casasola et al 2007 Torque map CO(1-0) PdB IRAM CO10CO21 CO in the inner ring at CR

22. 22 Driven Gas nuclear spirals Etherington & Maciejewski (2006) NGC 7217, HST dust spiral CO stalled in ILR

23. 23 CONCLUSION Molecular gas flows are observed in barred galaxies, they play a role in the fueling of nuclear starbursts and AGN Angular momentum transfer with DM or with outer disk according to mass ratio, concentration, kinematics Gas fraction able to destroy bars depend on the DM/disk ratio Torques computations in NUGA: most of the time, gas is stalled in rings at ILR or UHR resonances Embedded bars produce negative torques to the center

24. 24 Influence of the central potential on gas flows Dark matter with a core NFW dark matter profile More axisymmetry in the center stops the inner gas flow