Max Planck Institute for Astronomy - Annual Report 2005

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34 II. Highlights cretion disk, one not only obtains the temperature distribution of the dust torus (Fig. II.5.3), but one can also derive images of the radiation escaping at various wavelengths. Figure II.5.4 shows the expected images of the torus for Seyfert 1 (upper panel) and Seyfert 2 galaxies. Notice that at shorter wavelengths (λ � 5 µm) only the hot inner edge of the torus is discernible, while at longer wavelengths larger and larger regions of the torus are glowing. This is due to the decreasing temperature at increasing distances to the black hole. The second step takes into account that realistic dust tori are not filled homogeneously with gas and dust. As in the molecular clouds of our Milky Way, the dust will instead arrange itself in clouds or filaments. We therefore calculated how the total spectrum and appearances of the torus change when a clumpy dust distribution is assumed (Fig. II.5.5). We find that clumpy tori reproduce the spectrum observed from Seyfert 1 galaxies better than continuously filled ones. Whether the resolution of the VLTI is sufficient to find direct evidence of the clumpiness Seyfert 1 homogeneous Seyfert 2 homogeneous depends on the number of clumps the tori of nearby AGN are made of. In the third step we try to reproduce the dynamic processes that determine the structure and evolution of a torus in the central region of a galaxy. Stellar winds and planetary nebulae produce the dust. Supernovae provide the kinetic energy necessary to maintain the geometrically thick torus. Gravity and centrifugal force alone would create a thin disk from the inner edge of which matter would be sucked towards the black hole. Although our simulation will certainly not reach the spatial resolution needed to derive realistic images, we are confident that we will gain insight into fundamental properties and temporal variability of the tori in this way. Fig. II.5.5: The dust tori in Seyfert galaxies are probably not filled homogeneously with gas and dust, but rather have a clumpy structure. Model computations for types 1 and 2 at a wavelength of 12 µm yield the images shown here. Seyfert 1 clumpy Seyfert 2 clumpy 10 pc
Direct Detection of Dust Tori in Seyfert 2 Galaxies There are two good arguments for first searching for direct evidence for the existence of dust tori in Seyfert 2 galaxies. Firstly, the unified scheme of Seyfert galaxies rests on the hypothesis that the dust in Seyfert 2 galaxies is distributed in a donut-shaped structure. Secondly, here we expect the torus to clearly dominate the mid-infrared radiation, whereas in Seyfert 1 galaxies it will most likely be be outshone by the long-wavelength end of the thermal spectrum of the hot accretion disk. Our first successful observations with Midi were made in 2003. Based on observations of the archetypical and brightest Seyfert 2 galaxy, NGC 1068, carried out with only two telescope combinations, we were able to show that a dust structure whose warm component is heated by the AGN actually exists in its core. At a temperature of about 300 Kelvin, it has a diameter of 11 ly and an overall height of 6.7 ly. In addition, we detected a hot dust component 3 ly across at most, lying deeply embedded within the warm dust. We interpret this component as the signature of the dust located at the inner surface of the torus – the axial channel – which is heated to temperatures near the evaporation temperature for the dust particles of 1500 K. These findings unexpectedly closely match the prediction of our simple model (Fig. II.5.4). Though this should be qualified by emphasizing that with only two telescope combinations, it is impossible to determine the orientation of the dust structure independently. It was necessary to assume its symmetry axis based on the orientation of the known outflow phenomena in NGC 1068. During four observing campaigns, we meanwhile succeeded in observing the nearest Seyfert 2 galaxy – the Fig. II.5.6: Aperture coverage for the observations of the Circinus galaxy with Midi. Since each combination of telescopes is represented symmetrically with respect to the origin, the points cover twice the diameter of the entire telescope (see Fig. II.5.2). 0 10 30 50 m v u Total Flux [Jansky] Corellated Flux [Jansky] Visibility 15 10 5 0 1.5 1.0 0.5 0 0.2 0.1 0.0 8 II.5 Dust Tori in Active Galactic Nuclei 35 9 10 11 12 13 Wavelength [�m] Fig. II.5.7: Midi observations of the Circinus galaxy. Above: Total flux, measured with a single telescope. Center: correlated flux from two telescopes during one night, during which the projection on the sky of the baseline connecting the telescopes rotated from northeast-southwest (yellow) to southeast-northwest (pink). Below: the visibility – the quotient of correlated and total flux – is a coarse measure for the size of the torus. Circinus galaxy lying at a distance of just under 13 million ly – sufficiently often to be close to the ideal case of a well-filled aperture plane (Fig. II.5.6). For the first time, we are now able to reconstruct an image of the dust distribution without relying on model-dependent assumptions. The observed sequence of combinations of two telescopes with a total of 15 different orientations, each containing about 20 spectrally resolved, independent measuring points (Fig. II.5.7), in principle allows us to reconstruct a very detailed model of the two-dimensional (projected on the celestial plane) distribution of the dust (including the temperature). However, we decided to do simple image reconstruction first, which is independent of specific model assumptions as far as possible. We as
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Page 5: Contents Preface ..................
Page 8 and 9: 6 I. General I.1 Scientific Goals U
Page 10 and 11: 8 I. General massive protostars and
Page 12 and 13: 10 I. General achieve higher angula
Page 14 and 15: 12 I. General The institute is co-l
Page 16 and 17: 14 I. General Point Source sensitiv
Page 18 and 19: 16 I. General Edinburgh Groningen D
Page 20 and 21: 18 II. Highlights II.1 Light Echoes
Page 22 and 23: 20 II. Highlights 10 arcsec Fig. II
Page 24 and 25: 22 II. Highlights AB Dor C AB Dor A
Page 26 and 27: 24 II. Highlights II.3 The First He
Page 28 and 29: 26 II. Highlights II.4 Planetesimal
Page 30 and 31: 28 II. Highlights azimuthal directi
Page 32 and 33: 30 II. Highlights ticles fall faste
Page 34 and 35: 32 II. Highlights ANTU Seyfert 2 ga
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Page 40 and 41: 38 II. Highlights II.6 Massive Star
Page 42 and 43: 40 II. Highlights log M� /pc2 �
Page 44 and 45: 42 II. Highlights II.7 Observations
Page 46 and 47: 44 II. Highlights log IR luminosity
Page 48 and 49: 46 II.8 Dynamics, Dust, and Young S
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116 V. People and Events presented.
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144 Staff Directors: Henning (Actin
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146 Working Groups Rainer Lenzen, H
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148 Cooperation with industrial Fir
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150 Conferences Conferences and Mee
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152 Conferences D. Lemke: JWST-miri
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154 Conferences/Service in Comitees
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156 Publications Szalay, I. Szapudi
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158 Publications Hamilton, C. M., W
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160 Publications Brinkmann, D. G. Y
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162 Publications Zheng, X. Z., F. H
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164 Publications of the wheel mecha
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166 Publications ASP Conf. Ser. 331
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The Max Planck Society The Max Plan
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Max Planck Institute for Astronomy - Annual Report 2005

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