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Molecular gas flows in galaxies

Molecular gas flows in galaxies. Outline: Observational evidence Angular momentum transfers Bar destruction, role of gas, of DM AGN fueling, torques & NUGA. Françoise Combes Garching , 10 September 2007. Gas concentrations (CO emission).

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Molecular gas flows in galaxies

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

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

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

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

  5. Angular Momentum transfers 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 The gas loses its AM through gravity torques Viscous torques are in general negligible (Bournaud et al 05)

  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 (Ha) Action on the gas: sign of the torques, depending on the phase shift between gas and stellar potential NGC 7479

  7. DEC W+k/2 Gas at large scale? W W-k/2 2 patterns OLR of the 1st = ILR of the 2nd

  8. Bar strength No gas A RC A SF RC time 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 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. History of gas flows and accretion 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 Bars form, destroy and reform Heller, Shlosman & Athanassoula 2007

  10. Low importance of AM transfers with gas Transfer to DM more important (fgas < 8%) Berentzen et al 2007 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 *-gas * -DM

  11. Gas flows and AGN/SB feedback CR 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

  12. N6951: potential from red image CO in ILR ring Strength of the bar Q2= Ftan/Frad

  13. Torques computation Garcia-Burillo et al 2005

  14. N2782 nuclear disk + outflow Jogee et al 1999

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

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

  17. Stars Gas Zoom N2782:model 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. Nested bars in N2782 The CR of the nuclear bar Is the ILR of the primary bar Hunt et al 2007

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

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

  21. N3147: torques CO(1-0) PdB IRAM Torque map CO10 CO21 CO in the inner ring at CR Casasola et al 2007

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

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

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