molecular gas flows in galaxies françoise combes garching, 10 september 2007 outline: observational...
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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
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
Mtot
Mnuc
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 emissionRelated to secular evolution
PAH emission pseudo-bulgeNo 8 concentration classical bulgeSINGS (Spitzer)
N7331
N3627
N3351
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Formation of rings
Resonant rings (ILR, UHR, OLR),where gas is piling up
Trace of gravity torques
N1068 (BIMA)
IRAM (Schinnerer et al 2000)
NUGAN7217
N6951
N3147
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Angular Momentum transfers
The gas loses its AMthrough gravity torques
Viscous torques arein 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
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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
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DE
C
Gas at large scale?
2 patternsOLR of the 1st =ILR of the 2nd
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Bar destruction by gas
Gas is driven in by the bar torquesThe angular momentum is taken up by the bar wave fgas=6%
With negligible DMNo gas
A
RC
RC
ASF
Bar strength
time
This destroys the bar negative momentum inside CR
Not only the presence of the Central Mass ConcentrationEffect of gas depends on the cooling:Isothermal (RC) or adiabatic (A) Debattista et al (2006)
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History of gas flows and accretion
Heller, Shlosman & Athanassoula 2007
Bars form,destroy and reform
Gas accretes by intermittenceFirst it is confined outside OLR until the bar weakens,
then it can replenish the disk, to make it unstable again to bar formation
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Low importance of AM transfers with gas
Berentzen et al 2007Transfer to DM more important (fgas < 8%)
However,bar destroysmore quickly with gas
Interpreted asa function ofdestruction ofvertical resonance
Help of the CMC
Fgas should be higherIn presence of massiveDM
* -DM
*-gas
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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
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N6951: potential from red image
CO in ILR ringStrength of the barQ2= Ftan/Frad
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Torques computation
Garcia-Burillo et al 2005
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N2782 nuclear disk + outflow
Jogee et al 1999
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N2782: CO in the nuclear bar
Hunt et al 2007
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NGC 2782: torques
Torques are here systematically negativeDue to a secondary bar
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N2782:model
Stars Gas Zoom
Formation of aprimary bar anddecoupled 2ndbar in N-body+hydro simulation
Short phase, whentorques are negativedown to the verycenter
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Nested bars in N2782
The CR of the nuclear barIs the ILR of the primary bar
Hunt et al 2007
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N6574: CO and NIR
J-H from Kotilainen et al 2000
J and CO
CO in UHR ring and bar
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NGC 6574: torques
Qm
Phases
Torque map
Lindt-Krieg et al 2007
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N3147: torques
Casasola et al 2007
Torque map
CO(1-0) PdB IRAM
CO10 CO21CO in the inner ring at CR
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Driven Gas nuclear spirals
Etherington & Maciejewski (2006)
NGC 7217, HST dust spiral
CO stalled in ILR
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CONCLUSION
Molecular gas flows are observed in barred galaxies, theyplay a role in the fueling of nuclear starbursts and AGN
Angular momentum transfer with DM or with outer diskaccording 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 isstalled in rings at ILR or UHR resonances Embedded bars produce negative torques to the center
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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