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

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?

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.

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.

First images of NUGA project

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.

M=1 instabilities

•The distribution and kinematics of molecular gas reveal the onset of m=1 perturbations , shaped into one-arm spirals and lopsided disks in several galaxies. Perturbations appear at various scales, from several tens to several hundred pc.

NGC4826 NGC1961 NGC4579

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)).

Spiral arm structure detected in CO(2-1) (colour) is off-centred with respect to AGN locus (1mm continuum source-contours).

AGNAGN

Seyf 1LINERSeyf 2

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

NGC4826: the realm of m=1 perturbations

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...

•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).

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?

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).

M=2 instabilities

NGC6951 NGC2782 NGC3147

CO(2-1) map (color) shows regular two-arm spiral structure in the nucleus. Gas kinematics strongly disturbed (isovel contours).

AGN

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.

CO(1-0) map (color) shows nested two-arm spirals +compact source on AGN.

AGN

AGN

•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

Acoustic waves?

Most of the described gas perturbations observed in the first NUGA galaxies are probably linked with classical gravitational instabilities, except for NGC7217.

NGC7217

12co(2-1)

•12CO(1-0) map clearly shows molecular gas is related to the dust ring, but also to the filamentary stochastic multi-arm spiral pattern.

12CO(1-0) map overlaid with HST- V-I image

12CO(2-1) central source (contours) coincides with mini-spiral (?) seen in V-I color image.

NGC7217

LINER

Palomar-5m

Very regular LINER galaxy with 2 stellar /gas rings

Spiral structure insidethe ring, gaseous, mightbe due to acoustic waves

Slight oval distortion? A destroyed bar

NGC7217

An evolved system??

LINER

LINER

SEYF 2SEYF 2

SEYF 1/H

SEYF 1

--More observations are needed:-completion of the NUGA supersample-forthcoming observations (this winter) will reach subarsec resolution.

NUGA:(preliminary) conclusions on first results...

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?).

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 !

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.

The supersample: beyond NUGA