NUclei of GAlaxies (NUGA)

The IRAM survey of low-L AGN

Santiago GARCIA BURILLO

Observatorio Astronómico Nacional (OAN)-Spain

The NUGA teamS García-Burillo(1), F.Combes(2), A.Eckart(3), L.Tacconi(4), L.Hunt(5), S.Leon(6), A.Baker(4), P.Englmaier(7), F.Boone(8), E.Schinnerer(9), R.Neri(10).

(1)-OAN, Spain (2)-LERMA, France (3)-Universitaet zu Koeln, Germany (4)-MPE, Germany

(5)-CAISMI, Italy (6)-IAA, Spain (7)-Universitaet Basel, Switzerland (8)-Bochum University, Germany (9)-NRAO, USA

(10)-IRAM, France

FUELING AGN in SEYFERTS and LINERS

AGN fuelled with material originally away from gravitational field of BH: the problem of angular momentum removal.

Gravitational torques from large-scale (1 kpc) non-axisymmetric perturbations: density waves (m=2, m=1)+ interactions.

Weak correlation between 1kpc-scale perturbations and activity in ‘Local Universe’ AGN: Seyferts and LINERs.

Critical scale for AGN feeding: <100pc. AGN duty cycle is short!

Search for correlation with `secondary instabilities’ from 1 kpc to <100 pc: nuclear

bars? spiral gas waves?, nuclear-warps? m=1 modes? ... No consensus on the driving mechanism!...

Is the ‘inner playground’ (r<1 kpc) of low-L AGN different from ‘pure’ starburst or non-active galaxies?

Are all `secondary instabilities’ equally efficient feeding AGN?

Testing Unified Theories: differences between activity types (1 vs 2), gas tori sizes...

Open questions....

Where do we stand...?

CO: best tracer of distribution and kinematics of molecular gas in nuclei.

High spatial resolution (<1”) paramount to reach ‘critical’ scales: <50-100pc.

NUGA: first interferometric CO survey of a significant sample of AGN.

NUGA sample: 12 spirals ranging from Seyferts 1-2 to Liners. Previous surveys done with single-

dishes or restricted to a few AGN. Other interferometric surveys not focused on AGN (BIMA-SONG: Helfer et al 2003; OVRO-NRO: Sakamoto et al 1999, Baker et al 2003).

NUGA has a multi-wavelength approach : HST and ground-based optical/NIR images probe stellar

potentials and SF patterns to test the SB-AGN connection. Parallel VLA HI and VLBI radio surveys.

NUclei of GAlaxies: the NUGA project

NUGA: a Plateau de Bure CO survey of low-L AGN

NUGA: information from other wavelengths

• NUGA maps provide gas velocity fields and velocity dispersions. Advantage with respect to ‘only-HST’ surveys!.

Derivation of stellar gravitational torques on the gas: sudying the efficiency of AGN feeding

Numerical simulations of the gas dynamics based on stellar potentials compared with observations.

Evolution of instabilities.

NUGA diagnostic tools:

Full synthesis ABCD maps to be obtained for the bulk of the sample: PdBI high-sensitivity provide high-dynamic range images.

Twofold exploitation of NUGA data: ----1/Detailed case-by-case studies: NGC4826 (García-Burillo et al 2003, A&A,407), NGC7217(Combes et al 2003, A&A, in press), NGC1961 (Baker et al 2003 in prep), NGC3718(Krips et al 2003) ----2/Global exploitation of sample upon completion (early 2004?)

NUGA status

NUGA: the sample

LINER

LINER

LINER SEYF. 2

SEYF. 1

SEYF. 2

SEYF. 1

LINER/H

First images of NUGA

-Large variety of circumnuclear disk morphologies: m=2 instabilities (spiral arms, bars), axisymmetric rings, and m=1 instabilities.

First images of NUGA

•The new 0.5’’-0.7’’ maps reveal m=1 perturbations appearing as one-arm spirals and lopsided disks in several galaxies. Perturbations appear at various scales, from several tens to several hundreds of pc.

NGC4826 NGC1961 NGC4579

0’’.6 (=12pc) CO(2-1) map of NGC4826 shows molecular gas distribution strongly lopsided near AGN.

Seyf. 1LINERLINER

NUGA reveals m=1 instabilities

AGN AGN

AGN

20pc

150pc

500pc

0’’.7 (=180pc) CO(2-1) map of NGC1961 shows strong one arm spiral response

0’’.6 (=48pc) CO(2-1) map of NGC4579 shows m=1 instability in distribution+kinematics

LINER hosting 2 counter-rotating gas disks. Molecular gas disk corotates with stars.

NUGA maps show two m=1 spirals (Arms I-II; r>100pc) and a lopsided nuclear disk at r<40-50pc

Analysis of observed streaming motions suggests inner instabili-ties are ‘fast’ trailing m=1 pertur-bations...

Inner instabilities would not drive AGN fueling!.

Isovelocity maps in N4826

m=1 instabilities in NGC4826 (Garcia-Burillo et al 2003, A&A, 407)

NGC4826

Expected pattern of velocity perturbations due to m=1 spirals (slow/fast) according to DW linear models. For fast ‘modes’ m=1 develops mostly outside corotation.

Calculation of stellar gravitational torques on the gas:

Can these contribute to AGN feeding?

Gravitational torques change of sign for Arm I and Arm II: agreement with CO-based diagnostics.

Efficiency of torques is very low: at R=200 pc, angular momentum transfer significant on scales of 1Gyr!

AGN feeding seems negligible for r<50pc!--->new 0.6’’ observations will help to reassess feeding issue.

m=1 instabilities in NGC4826 (Garcia-Burillo et al 2003, A&A, 407)

Gravitational torques

•NIR HST image--->M/L ratio fit on rotation curve-->Fourier decomposition...

Stellar perturbations seem inefficient to drive angular momentum transfer.

While stellar potential inefficient, is gas self-gravity potentially important?

Estimate of Toomre Q parameter for the gas disk:

CO-->Ngas and Qgas:

•1/Arm I-II have very low Q ( close to 1)

•2/Lopsided instability in nuclear disk may have Q<2-3

Previous claims from HST analysis of colour maps in AGNs: Q=10-100!

Gas self-gravity of observed instabilities might favour/inhibit AGN feeding?

--->to be explored in numerical simulations

Q maps in NGC4826:

m=1 instabilities in NGC4826 (Garcia-Burillo et al 2003, A&A, 407)

Gas self-gravity

NGC7217

12CO(1-0) (top) and 12CO(2-1) (bottom) maps overlaid with HST V-I image

Rings and spirals in NGC7217 (Combes et al 2003, A&A, in press)

LINER with high degree of axisymmetry. Halo+bulge dominant. It has 3 stellar rings but paradoxically no strong bar!

NUGA 1-0 map shows molecular gas in circular ring (m=0) covering nuclear dust ring and multi-arm spiral pattern identified by HST.

Little gas near AGN source. Nuclear spot seen in 2-1 and 1-0 of < 106 solar masses. Associated with stochastic mini spiral seen by HST.

Inner boundary of molecular ring is very sharp!:...

. Evidence that AGN fueling is negligible inside the ring at present!

Rings and spirals in NGC7217 (Combes et al 2003, A&A, in press)

Numerical simulations

The N7217 paradox: 3 contrasted rings but no bar at present!

N-body simulations including stars+gas self-gravity and star formation explore two extreme models to account for `present’ morphology:

--1/Run A: mild persistent oval.

--2/Run B: strong bar dissolved after gas

infall

Mild oval model is favoured. Nuclear gas ring formed near ILR of oval distortion. Gas piles up on the inner side of the ring:...

....no significant AGN feeding at present !

Run A

Run B

Caught in the act: evidence for asymmetrical feeding? NGC6951

NGC4579

Schinnerer et al 2003 in prep

García-Burillo et al 2003b in prep

--More observations are needed:-completion of the NUGA supersample

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).

Wide range of morphologies

No clear EVOLUTIONARY SEQUENCE emerges thus far. WHY?AGN sate is episodic + The problem of time-scales.

Summary and conclusions

Global exploitation of NUGANUGA aims at compiling sample of 25-30 galaxies by including PdBI data available from consortium members. Availability of non active galaxies crucial to build up comparison sample.

The NUGA supersample

•Diagnostic of streaming motions for m=1 perturbations easiest along minor axis.

1/Inner arm (I) would be a fast trailing mode (developing outside corotation).

2/Outer arm (II) would be a slow trailing mode (developing inside corotation). 3/The lopsided m=1 mode of the circumnuclear disk would be a fast trailing mode.

•Position-velocity strips along minor axis in the 1-0 line (top) and 2-1 (bottom)

NGC4826: streaming motions and m=1 perturbations

•Diagnostic of streaming motions indicate that there might be 2 distinct velocity patterns if (big IF!) the m=1 perturbations are real modes : •Inner modes being fast, cannot help in fueling AGN. •Outer modes being slow, can help however.

•The expected pattern of velocity perturbations due to m=1 spirals (slow/fast) according to DW linear models

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

NUclei of GAlaxies:N4826-paper I

CURRENT STATUS: submitted 07-feb-03•First complete draft by December 02 written by SGB (except for section 4 mostly due to LKH).•Comments received from December 02+January 03.•New version takes into account a fair amount of your comments.

-----1/A new subsection 6.1 dealing with gravitational torques (FC).

-----2/New organisational scheme: sections split into a larger number of subsections (ES).

-----3/Many other items (FC,LKH,AB,ES,SL,RN,FB,PE).

Forthcoming work on ngc4826•I/ Future A-configuration data next month (?) reaching <0.5’’(=10pc)•II/ Future numerical simulations. Probably I+II/= a second paper this year

NGC4826

•Black Eye=Evil Eye galaxy=Inner disk shows strongly disturbed dusty morphology. A dust lane arc goes across the northern side (r=10”-20”)

•(R)SA(rs)ab hosting two counterrotating gaseous disks, where the inner gas disk (both neutral and ionised at r<30’’ =1 kpc) corotates with the stars. The outer gas disk (HI) from 80’’ to 9.8’ counterrotates with the stars.

•Transition region (30’’--100’’) identified by kinematical disturbance in Halpha: radial inflow

•Activity=LINER nucleus (starburst dominated?).

Molecular gas distribution in NGC4826

•The total molecular gas mass in the primary beam Mgas= 2.3x108 M .

•Little is left outside the 1-0 primary beam.....Confirmed by comparison with single-dish+OVRO+BIMA maps

•We confirm that there is no two stream flow in the inner disk: CO/HI/Halpha corotate with the stars (r<30’’)

NGC4826: where is the AGN?

VLA image of NGC4826 showing non-thermal emission (6cm). Cross=

position of dynamical center, based on ‘CO diagnostics’

Determination of dynamical center

•Maximum line widths (second order moments) + maximum symmetry on C(-3.3, -0.8).

•Non-thermal source (6cm) on C

•X-ray Chandra source on C

•Blue (B-I) point-like source on C

Molecular gas distribution in NGC4826

12CO(2-1)

•12CO(1-0) map (2.9”x2.4”) shows molecular gas concentrates in a lopsided circumnuclear disk (CND) with Mgas= 3.4x107 M and r=2’’-3’’(40-50pc), and two one arm spirals=Arm I and II developing at different radii out to r=(35’’) 700 pc.

•High-resolution(1.1”x0.8”) 12CO(2-1) observations fully resolve the inner disk revealing a lopsided instability (m=1 perturbation).

•The central source does not peak at the dynamical center. The lopsided instability stretches out from a radius of 50pc to 100pc)

•Previous HCN observations of the nucleus (Helfer and Blitz 1997, ApJ 478) showed a strong lopsided morphology.

•Higher-resolution observations (A configuration) are foreseen to reach <0.5’’=10pc!.

CND

NGC4826: m=1 perturbations: Arm I and Arm II

•Peak brightness maps in the 1-0 line (top) and 2-1 (bottom) with the same asymmetries revealed

•Log (radius) -Azimuth plots for the 1-0 (top) and 2-1 (bottom) maps allow to identify the different m=1 perturbations:•I/ The m=1 inner spiral: Arm I is detected in the S side and in 2-1 and 1-0. Arm I is trailing (N side is closer).•II/ The m=1 outer spiral: Arm II mostly detected in 1-0, though beginning present in 2-1. Arm II is first trailing (II a) but ‘changes’ to leading (II b) orientation outward!

•Is there any ‘radial’ overlapping between I / II? •What are the implications of II_ _b/II_a?---transition region?

NGC4826 :Distribution of star formation

•Asymmetries in star formation patterns are real and not mere artifacts due to extinction!

•Asymmetrical patterns in the disk are followed with similar spatial scales by star formation tracers (see Pa map):

•m=1 arms: Arm I and Arm II. •North-South asymmetry at odds with any expectation from extinction.•Inner disk in Paschen_alpha is lopsided with strong maximum 20 pc northward from AGN.

We overlay the 1-0 (top) / 2-1 (bottom) Bure maps with the Paschen_alpha image obtained from HST

We overlay the 2cm emission contours (mostly thermal) with the Paschen_alpha image obtained from HST

NGC4826:Star formation and Compact Star Clusters (CSCs)

Extinction in the Evil Eye•The strongest absorption (red color) on the North side of the disk does not correlate strongly with CO arm:...linked with HI gas instead??.•CO based-Av map weakly correlated with (B-I)-based Av map .

•We overlay the 1-0 (top) / 2-1 (bottom) Bure maps with the B-I color image obtained from HST data.

Star formation and CSCs•SFR=0.14 Msun/yr implies vigorous SF in the inner disk fed by molecular gas.•Trend along minor axis for hardness of ionising ratio, with softening towards a ridge at r=17’’ (where CO disk ends): ridge of CSCs.•SF disk is truncated at r=17’’, beyond a ridge of old (>10Myrs) CSC.

NGC4826: HST-Nicmos images: the inner stellar disk

•We overlay the 1-0 (top) / 2-1 (bottom) Bure maps (in contours) with the USM image obtained from HST-NICMOS data (F160W filter) (color scale).

•HST-NICMOS map (F160W filter) (color scale) in the inner disk of NGC4826.

The origin of m=1 perturbations in NGC4826

Origin of m=1 perturbations in N4826:•The kinematics (streaming motions) are ‘compatible’ with the velocity patterns expected for:

1---Fast m=1 modes in the inner disk (50-500pc) This is contrast to m=1 modes driven to counterrotation where pattern speeds very low.

2---Slow m=1 modes in the outer disk (500pc-1.5kpc)

• No two-stream flow in inner disk: unless detection of counterrotating stellar disk elusive•Numerical simulations will test the viability of other mechanisms favouring m=1 instabilities (see Shu et al 90; Junqueira and Combes, 1996).•Disks with high gas content DO favour the onset of fast m=1 modes close to the nucleus.

•Several lines evidence for a past gas accretion episode:

1/Counter-rotating outer disk

2/Infall motions (R=30’’-100’’)

3/Molecular gas+SF disk truncated (R<35’’)

4/’Cold’ stellar disky component (R<30’’)