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

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)

NUGAN7217

N6951

N3147

5

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

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

DE

C

Gas at large scale?

2 patternsOLR of the 1st =ILR of the 2nd

8

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)

9

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

12

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

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 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

18

Nested bars in N2782

The CR of the nuclear barIs the ILR of the primary bar

Hunt et al 2007

19

N6574: CO and NIR

J-H from Kotilainen et al 2000

J and CO

CO in UHR ring and bar

20

NGC 6574: torques

Qm

Phases

Torque map

Lindt-Krieg et al 2007

21

N3147: torques

Casasola et al 2007

Torque map

CO(1-0) PdB IRAM

CO10 CO21CO in the inner ring at CR

22

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