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NUclei of GAlaxies: First results of NUGA

NUclei of GAlaxies: First results of NUGA. Santiago GARCIA BURILLO (burillo@oan.es) Observatorio Astronómico Nacional (OAN). The NUGA project People involved :

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NUclei of GAlaxies: First results of NUGA

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  1. NUclei of GAlaxies:First results of NUGA Santiago GARCIA BURILLO (burillo@oan.es) Observatorio Astronómico Nacional (OAN) The NUGA project People involved : S García-Burillo(1), F.Combes(2), A.Eckart(3), L.Tacconi(4), L.Hunt(5), S.Leon(3), A.Baker(4), P.Englmaier(4),F.Boone(2),E.Schinnerer(6), R.Neri(7). (1)OAN- Observatorio Astronomico Nacional, Madrid, Spain(2) LERMA, Observatoire de Paris, France (3) I. Physikalisches Institut, Universitaet zu Koeln, Germany (4) MPE, Garching, Germany (5) CAISMI-CNR, Florence, Italy (6) Caltech, USA (7) IRAM, Grenoble, France

  2. FUELING THE AGNs IN SPIRALS • AGN are fuelled with material(gas/stars) originally lying away from the gravitational field of the BH. • For gas in-fall to occur we need to remove angular momentum. • There is no consensus on the mechanisms driving the in-fall of gas towards the central BH: do they depend on AGN luminosity/type?: • I/High-luminosity AGNs need large accretion rates (102-3 M/yr) which must involve large-scale gravitational instabilities. These can trigger a nuclear starburst. Mass-loss rate/stellar collisions/disruptions may account for the necessary fuel. • I/Low-luminosity AGNs(Seyferts 1-2 and Liners) :although they need smaller accre-tion rates (10-2 -10-1 M/yr), these probably involve also large-scale gravitational instabilities: nuclear SB comes first? • Different types of large-scale gravitational instabilities have been described for AGN in spirals: • 1/Large-scale stellar bars: gas infall may stop at ILR barrier (Combes and Gerin 85) • 2/Decoupled nuclear bars stellar (Friedli and Martinet 93) or gaseous (Shlosman et al 89) may drive gas to smaller scales < 100pc. • 3/Spiral gas waves: probably effective at small scales effective even for low Mgas/Mtot ratios (Englmaier and Shlosman 2000) . • 4/Micro-warps:driven by pressure effects (Pringle 1996, Schinnerer et al 2000). • 5/Lopsided/m=1 instabilities: either related to indirect potentials due to off-centring of central mass (Shu et al 90), counter-rotation (Garcia-Burillo et al 2000) or BH-dominated potentials (Bacon et al 2000). • Are large-scale instabilities different for Seyf 1, 2, and Liners? (and starburst galaxies?) • Are they equally efficient in driving the gas inwards? • Are molecular gas tori in Seyferts extended to several hundred pc?

  3. NUCLEI OF GALAXIES : the NUGA project NEED OF A HIGH-RESOLUTION CO SURVEY: No interferometric CO survey of a significant sample of AGNs has ever been published so far-Previous surveys: done with low-resolution single-dish antennas (studying molecular gas on kpc scales). High spatial resolution(<1”) will allow study of molecular gas distribution/kinematics on scales <50-100pc. restricted to very few cases (poor statistics). See ongoing AGN surveys with OVRO (Baker et al,2000-2002)-NUGA sample=12 nearby AGNs covering the whole sequence of activity types (1, 2, 3=Liners)-NUGA aims at enlarging the sample to 25-30 galaxies by adding available data on AGNs observed by consortium members. Non active galaxies are also available (comparison sample)  CO maps provide information on the gas kinematics: velocity fields, velocity dispersions....-Essential to characterise gravitational instabilities COMPLEMENTARY INFORMATION FROM OTHER WAVELENGTHS: NUGA has a multi-wavelength approach: HST and ground-based optical/NIR images available to derive stellar potentials/SF patterns, ... CO observations can be confronted to numerical simulations of gas dynamics based on stellar potentials derived from NIR images.

  4. NUCLEI OF GALAXIES : the NUGA sample High-sensitivity of Bure array can give high-dynamic range images after a standard synthesis.-The survey will provide a unique data set to be fully exploited on a detailed case-by-case basis, and globally as a homogeneous sample of nearby AGNs.

  5. First images of NUGA project

  6. First images of NUGA project -The variety of morphologies of circumnuclear gas disks is remarkably large: unresolved compact sources, nuclear spiral arms, rings, lopsided and other asymmetric features.

  7. M=1 instabilities • The distribution and kinematics of molecular gas reveal the onsetofm=1 perturbations , shaped into one-arm spirals and lopsided disks in several galaxies. Perturbations appear at various scales, from several tenstoseveral hundred pc. Seyf 2 LINER Seyf 1 NGC4826 NGC1961 NGC4579 AGN AGN  Spiral arm structure detected in CO(2-1) (colour) is off-centred with respect to AGN locus (1mm continuum source-contours).  CO(2-1) map (contours) overlaid on Palpha HST image. Lopsided inner disk+one-arm spiral echoed by star formation. One-arm spiral revealed by CO distribution + kinematics (top) is detected in UMT HST NICMOS image (bottom)). 

  8. NGC4826: gas velocities • Both m=1 spirals (arms I/II) are revealed by noncircular motions. • Noncircular motions are also associated with the nuclear lopsided disk. • We have compared the observed deviations with the expected velocity residuals for stationary and fast m=1 modes, either trailing or leading with respect to the gas flow. Velocity patterns of stationary/fast m=1 modes, trailing/leading with respect to the gas flow. Isovelocity maps in N4826

  9. NGC4826: the realm of m=1 perturbations • Do we expect the onset of a counterrotating instability in the inner disk where there is no two-stream flow?? Is there a missing (undetected) counterrotating stellar disk in the inner regions? • Numerical simulations will test the viability of counterrotating instabilities in a N4826-like case... • Discuss other mechanisms favouring m=1 modes (see Shu et al 90; Junqueira and Combes, 1996). • m=1 modes in N4826: • The distribution and kinematics of molecular gas reveal several m=1 modes (slow and fast). • ---Fast m=1 modes in the inner disk (50-500pc) • ---Slow m=1 modes in the outer disk (500pc-1.5kpc) • Although N4826 has a counterrotating HI disk, the m=1 modes observed in CO disk may not due to counterrotation, however...  • AGN fueling • Inner m=1 mode being fast, might not cooperate in AGN fueling (problem??) • Are (all kind of ) m=1 modes older than m=2 perturbations?

  10. NGC4826 :star formation patterns • Asymmetrical patterns in the disk are mimicked by star formation tracers, such as Paschen_alpha (color image): • m=1 outer arm • off-centered bar-like structure • inner disk in Paschen_alpha appears strongly lopsided • We overlay the 1-0 (top) / 2-1 (bottom) Bure maps with the Paschen_alpha image obtained from HST data (Boeker et al 1999).

  11. M=2 instabilities • m=2 perturbations such as two-arm spirals or gaseous bars dominate the response and kinematics of the gas in other galaxies. Seyf 2 H/Seyf 1 Seyf 2 NGC6951 NGC2782 NGC3147 AGN AGN AGN  CO(1-0) map (color) shows nested two-arm spirals +compact source on AGN.  CO(2-1) map (color) shows regular two-arm spiral structure in the nucleus. Gas kinematics strongly disturbed (isovel contours). CO(1-0) map (top) shows nuclear gas bar+outer spiral. CO(2-1) map (bottom) resolves inner disk into nuclear gas bar+mini two-arm spiral. 

  12. NGC7217 Acoustic waves? Most of the described gas perturbations observed in the first NUGA galaxies are probably linked with classical gravitational instabilities, except for NGC7217. LINER • 12CO(1-0) map clearly shows molecular gas is related to the dust ring, but also to the filamentary stochastic multi-arm spiral pattern. NGC7217 12co(2-1) 12CO(2-1) central source (contours) coincides with mini-spiral (?) seen in V-I color image.  12CO(1-0) map overlaid with HST- V-I image

  13. NGC7217 Very regular LINER galaxy with 2 stellar /gas rings Slight oval distortion? A destroyed bar Spiral structure inside the ring, gaseous, might be due to acoustic waves An evolved system?? Palomar-5m

  14. SEYF 1/H LINER SEYF 1 SEYF 2 SEYF 2 LINER

  15. NUGA:(preliminary) conclusions on first results... Wide range of morphologies detected... -----Are AGN nuclear gas disks different from starbursts or normal galaxies at scales of tens-to-hundred parsecs?-----Any difference among the different activity types?No clear PICTURE /EVOLUTIONARY SEQUENCE emerging (so far!).WHY??--- AGN sate is episodic + gravitational instabilities are known to change during the evolution of galaxy disks: Are different mechanisms of fuelling acting at different epochs? The problem of time-scales.---Our Galaxy is known to have (at the same time!)a large-scale bar+a nuclear bar+a m=1 inner mode ! Importance of m=1 instabilities: one-arm spirals, lopsided disks ...In some cases, they do not help fuelling AGN however  Most of m=1+m=2 perturbations described are roughly self-gravitating structures (low Q). With notable exception:N7217 (evidence of acoustic waves?). --More observations are needed: -completion of the NUGA supersample -forthcoming observations (this winter) will reach subarsec resolution.

  16. The supersample: beyond NUGA NUGA aims at enlarging the sample to 25-30 galaxies by adding available data on AGNs observed by consortium members. Non active galaxies are also available (comparison sample). We have compiled a tentative first list of 16 possible candidates to be included/added in a follow-up study.

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