NIR interferometry of

the Seyfert galaxy NGC 1068:

present interferometric NIR results and

future goals

G. WeigeltT. Beckert

M. Wittkowski

Infrared interferometry and theoreticalstudies of the environment of AGN:

→ structure of the dust environment,

→ evolution fuelling & growth of the BH

Activity in the centres of galaxies manifests itself in the form of both

• non-stellar nuclear activity (AGN, i.e. BH, accretion disk, BLR, torus, NLR..),

• and of circumnuclear star formation (starburst).

AGN activity is caused by accretion into a super-massive BH, whose evolution is driven by this accretion.

We can investigate, by the combination of interferometric observations and theoretical studies, how accretion processes at different length scales work and how they relate to each other.

The length scales of interest range from :

• approx. 100 pc – where starbursts may dominate the appearance – • to a few pc - where a dusty torus is the main component • and to the centre of the AGN with outflows and jets.

Physical torus models and radiative transfer modelling

K-band speckle interferogram of NGC

1068:

exposure time 200 ms,FOV 1.8 x1.8 ’’

1.8’’

Observations: Bispectrum speckle interferometry of NGC 1068 with the SAO 6 m telescope

First resolution of NGC 1068

Azimuthally averaged visibility of NGC 1068 (top) and an unresolved reference star (bottom)

Wittkowski et al. A&A 329, L45, 1998

1999: Weinberger et al. confirmed this result (AJ 117, 2748)

FWHM Gauss fit

diameter 30 mas ~ 2 pc!

Bispectrum speckle interferometry of NGC 1068:

First diffraction-limited,elongated K-band image

of NGC 1068

(Wittkowski et al. 1998, A&A 329, L45)

extension at PA ~ - 20o

NGC 1068:

visibility functions derived

from 4 different data sets

Weigelt et al. 2004

19 x 40 mas

20 x 40 mas

24 x 40 mas, 600 frames, 2’’ K-band seeing

18 x 38 mas ~ 1.5 x 3 pc

error +/- 4 mas

11 000 frames,

1.2’’ seeing

major axis

minor axis

K-band flux of the 18 x 39 mas object

~18 %

Photometric K-band results

Flux in ratio in 2.5’’ FOV:

Total flux: phot. calibrators

18 x 39 mas: 82% = 350 mJy

Extended components: 70 mJy

H-band visibility of NGC 1068

FWHM Gauss fit diameter: 18 x 45 mas (+/- 4 mas)

Real-timeReal-time Bispectrum Bispectrum Speckle InterferometrySpeckle Interferometry

Data recording and data processing: ~ 2 frames/s Data recording and data processing: ~ 2 frames/s SAO 6 m telescope, 2 arcsec K-band seeing, 76 mas resolution SAO 6 m telescope, 2 arcsec K-band seeing, 76 mas resolution

Bispectrum speckle

interferometry:

First diffraction-limited

K‘- and H-band images of the

resolved 18 x 39 mas core of NGC

1068

The images show the compact core

with its tail-shaped, north-

western extension at PA of -16o as

well as the northern and south-eastern

extended components.

Weigelt et al. 2004 (A&A 9/2004)

Diffraction-limited K’- and H-band images of NGC 1068

PA ~ -16o

Compact component: 18 x 39 mas ~ 1.3 x 2.8 pc

Northern component: 400 mas

Northern 400 mas object North-western

tail of the compact

18 x 39 mas

object

Summary: H- and K-band bispectrum speckle

interferometry of NGC 1068:

57 mas / 74 mas resolution images

● A diffraction-limited K'-band image with 74 mas resolution and the first H-band image with 57 mas resolution were reconstructed from speckle interferograms obtained with the SAO 6 m telescope.

● The resolved compact core has a north-western, tail-shaped extension

Bispectrum speckle interferometry method: Weigelt, Optics Com. 21, 55, 1977; Lohmann et al. Appl. Opt. 22, 4028, 1983

Summary: Bispectrum speckle interferometry of NGC 1068:

1.3 x 2.8 pc core ► The K'-band FWHM diameter of the resolved compact core is 18 x 39 mas or 1.3 x 2.8 pc (FWHM of a Gaussian fit; fit range 30-80% of the telescope cut-off frequency).

► The diameter errors smaller than ± 4 mas.

► The PA of the north-western extension is -16 ± 4o.

► In the H band, the FWHM diameter of the compact core is 18 x 45 mas (± 4 mas), and the PA is -18 ± 4o.

► The extended northern component (PA ~ 0o) has an elongated structure with a length of ~ 400 mas or 29 pc.

► The K'- and H-band fluxes of the compact core are 350 ± 90 mJy, or K‘ = 8.2, and 70 ± 20 mJy, or H = 10.4, respectively.

Comparison with HST, Merlin, and VLBA

images

200 mas

100 mas VLBA 8.4 GHz radio continuum; Gallimore et al. 1997: ~ 5 x 20 mas

Heat image: HST 502 nm

MERLIN 5 GHz,

Muxlow et al. 1996

S1

C

Ionization cone

MERLIN 5 GHz contour map(Gallimore et al.1996) superposed

on our K'-band image.

The center of the radio component S1 coincides with the center of the

K'-band peak. The P.A. of –16o of the 18 x 39 mas K'-band core is very

similar to that of the western wall (PA

-15o) of the ionization cone. The northern extended 400 mas structure (red) aligns with the direction of the inner radio jet (S1 - C). The northern borderline of the northern component is almost perpendicular to the radio

jet direction between C and NE.

Interpretation

The PA of -16 ± 4o of the compact 18 x 39 mas core is very similar to that of the western wall (PA = -15o) of the ionization cone.

This suggests that the H- and K'-band emission from the 18 x 39 mas = 1.3 x 2.8 pc core is both thermal emission & scattered light from ● dust near the western wall of a low-density, conical outflow cavity or from ● the innermost region of a pc-scale dusty torus heated by the central source.

The dust sublimation radius of NGC 1068 is approximately 0.2 – 1 pc.

The northern extended 400 mas structure lies near the western wall of the ionization cone and coincides with the inner radio jet (PA = 11o). The large distance from the core suggests that the K'-band emission of the northern extended component is scattered light from the western cavity region and the radio jet region.

Interpretation: Flux and structure predicted by various torus models

For a quantitative analysis of the K'-band flux emerging from the optically thick torus, accurate radiative transfer modeling is necessary. A number of models have been published for NGC 1068 (Pier & Krolik1992, 1993, Granato & Danese1994, Efstathiou & Rowan-Robinson 1995, Efstathiou et al. 1995, Granato et al. 1997, Manske et al. 1998, Nenkova et al. 2002, Galliano et al. 2003). All these models try to fit the SED of Rieke & Low (1975) with a K-band flux of 0.3 Jy.

Most authors introduced in their extended torus an additional dust component located within the ionization cone to reach the required K band flux.

Torus models which can explain the observed infrared SED by emission solelyfrom the torus (i.e., without dust within the ionization cone) were presented by Granato & Danese (1994).

A simulated 2.2 μm image reported by Granato et al. 1997 shows an elongated shape along the direction with low absorption. The model images are equal or somewhat larger than the dust sublimation radius). As discussed above, our images of the compact core also have a size which is similar to the dust sublimation radius.

First VINCI-VLT interferometry of NGC 1068:resolution of a new 0 - 5 mas structure (46 m baseline, K band):

3 mas clumps in the torus? Accretion disk?

Wittkowski, Kervella, Arsenault, Paresce, Beckert, Weigelt 2004, A&A 418, L39

6 m telescope / speckle VINCI VLTI, 46 m

30 mas

3 mas or 0.1 mas ?

First MIDI-VLT interferometry of NGC 1068

Resolution of two components:

- Central hot component: Dust temperature > 800 K

Size: 0.7 x <1 pc (0.7 pc parallel jet)

Hot inner torus wall?

- Large warm component: T = 320 K

Size 2.1 x 3.4 pc

Jaffe et al. 2004, Nature 429, May 6

hot comp.

warm

42 m baseline

72 m baseline

Science goals of

next generation interferometric facilities?

• Testing the unification scheme and torus models (clumpy tori)

• Physical properties of outflows and jets

• AGN – starburst connection

• Nuclear disks, their evolution, and black hole fuelling & growth

• Connection between massive, large-scale gas disks with starbursts, dusty tori, and AGN activity

(BLR: talk by Alessandro Marconi)

Testing the unification scheme and torus models

Based on the pioneering work of Miller and Antonucci (Miller et al. 1983, Antonucci

et al. 1985), the major difference between type 1 and type 2 AGN is attributed to

aspect-angle-dependent obscuration effects by a dusty torus.

For more than a decade, clumpy models for the circumnuclear torus have been

under discussion (Krolik & Begelman 1988). However this idea was not included

in the first radiative transfer calculations (Pier & Krolik 1992, 1993; Granato &

Danese 1994; Efstathiou & Rowan-Robinson 1995) of dust emission from these tori.

Only recently, Nenkova et al. (2002) developed a scheme which uses the

clumpiness of the torus for an approximative and statistical treatment of the

radiative transfer problem with optically thick clouds.

dust sublimation radii

K-band brightness distribution of our radiative transfer calculations based on the method of Nenkova et al. (2002) (Beckert et al. 2004).The inclination is 20o from the midplane (contour range of 213).

Physical properties of tori and radiative transfer modelling

Vollmer et al. (2004) and Beckert & Duschl (2004) and other authors reported stationary models of obscuring dusty tori around AGN. Such (more realistic)

models are required as input for radiative transfer modelling.

● The key ingredient of the model is the clumpiness of the torus in which dusty

molecular clouds move with a high velocity dispersion.

● Within the model, the radial accretion flow is seen as a consequence of cloud-

cloud collisions, which can redistribute angular momentum.Accretion in the combined gravitational potential of a central black hole and

stellar cluster transfers gravitational binding energy to random kinetic energyand maintains the thickness of the torus.

Cut through the probability distribution of finding a dusty cloud in the torus. The distribution is derived from the model of Beckert & Duschl (2004).The spatial scale is in units of the dust sublimation radius. The mean number of clouds along a line of sight to the centre drops

below 1 for angles larger that 40o from the midplane.

Theoretical studies of tori

dust sublimation radii

K-band brightness distribution of a radiative transfer model based on the method of Nenkova et al. (2002) (Beckert et al. 2004).The inclination is 20o from the midplane (contour range of 213).

Interferometric/theoretical studies of the AGN – starburst connection

The effects of star formation on the gas dynamics and the star formation rate can most likely influence the channelling of matter to the centre (e.g., Vollmer &

Beckert 2003).

● However, it is difficult to establish a direct causal connection between starburst and AGN activity (Knapen 2004); since the steering of turbulence and subsequent transport of gas to the centre happens on a viscous transport time scale, which introduces a yet unknown time

lag between starburst and AGN activity. Therefore, any causal connection between a starburst and the AGN is difficult to test.

● We need studies of the gaseous and dusty AGN environment during the accretion

of mass by the central black hole (in the continuum and in emission lines).

Nuclear disks, their evolution, and their relation to starbursts

It seems that black holes in the local universe have predominantly increased their mass by accretion (Marconi et al. 2004). The existence of

black holes with masses >109 solar masses in the quasars with the highest known redshifts (i.e., young objects) indicates that the viscous time scales

for very massive disks have to be remarkably short, much shorter than predicted by standard disk models (e.g., Shlosman, Frank, & Begelman 1989).

● The original interpretation that this is indicative of non-axisymmetric processes has,

however, become questionable by the finding that the bar fraction in AGN disks is not considerably higher than in normal galaxies (e.g., Martini et al. 2003).

● Alternative? It has been shown that self-gravity of disks may also enhance the radial mass

transport (Duschl, Strittmatter & Biermann 2000; Duschl 2004). An interesting

feature of these self-gravitating disks is that the transport of angular momentum is

more efficient and that material from the outer disk regions will accrete more

efficiently than that at smaller radii. Self-gravity in massive gaseous disks will lead to gravitational instabilities and star formation.

Interferometry and theory: the connection between massive gas disks, starbursts, dusty tori, and AGN

activity?

● The properties of the circumnuclear dust distribution (e.g., torus, outflow

cavities, etc.) derived from observations and modelling can be related to the

luminosity and morphology of circumnuclear star forming regions. This will provide

constraints for a scenario which connects the time evolution of gas from large

scales to the activity in the centre.

● The observable properties of the circumnuclear star formation regions will

provide constraints for the dynamical models of massive gas disks discussed

above. In particular, the location of the inner edge of a starburst ring will allow us to

determine where self-gravity becomes important in the disk and thus to get

information about the mass distribution in the disk.

AMBERAMBER

Observation of 51 Hya:

Commissioning May 2004

Medium spectral resolution R=1200

K‘ band (2.0-2.3 μm)

Two 8.2 m UTs equipped with MACAO AO

Next generation facilities

Size and shape of tori: 100 m baseline four 8 m telescopes imaging (visibilities + closure phases)

Detailed structure of tori (clumpiness, outflow cavities): 1 km baseline > 10 telescopes imaging

BLR: size of the nearest BLRs (~ 0.1 mas): 100 m baseline if differential visibilities and phases are measured detailed structure: 1 to 10 km baseline