Max Planck Institute for Astronomy - Annual Report 2005

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36 II. Highlights 8.5 �m 2.3 ly 0 . � 02 sume that the brightness distribution of the dust emission can be approximated in all projections and all wavelengths by a Gaussian function. Under this assumption, the visibility observed (Fig. II.5.7) can be converted directly into a measurement of the effective width. The points in Fig. II.5.8 represent this reconstructed effective size of the dust distribution in the Circinus galaxy for two wavelength ranges (λ � 8.5 and 13µm, cf. Fig. II.5.7). These wavelengths are nearly unaffected by absorption through silicate-dust grains. With the help of this simple image reconstruction, we find the distribution of the dust to be box-shaped both at a wavelength of 12.5µm (dominated by dust at about 300 K) and 8.5µm (hotter dust). At 12.5µm, the observed dimension of the box is 50�30mas, corresponding to a diameter of 3.2ly and a height of 1.9ly. The size and orientation match other observations of the nucleus of the Circinus � � 13 �m 1.5 ly Fig. II.5.8: From the measured visibility (Fig. II.5.7) the effective size of the dusty torus of the Circinus galaxy can be derived – here shown for two wavelenghts. At the larger wavelength the torus appears larger – as expected. Fig. II.5.9: The axis of symmetry of the ionized cone in the Circinus galaxy imaged by the HST is exactly perpendicular to the dursty torus, as reconstructed from the Midi data. Note the different scales. 1 ly H � 60 ly � 3.6 ly 2.3 ly galaxy (Fig. II.5.9): For example, the symmetry axis of the ionization cone observed with HST is exactly perpendicular to the maximum extension (the plane of the torus) found. In addition, the region where Maser emission of molecular H 2 O gas was found in well-ordered rotation exactly corresponds to our dust distribution. This proves that water vapor and dust are concentrated in the same regions. The actual vertical dimension of the dust distribution still has to be examined since an apparent height could be feigned by an inclined disk. Applying the most probable value for the orientation of the symmetry axis with respect to our line of sight (70 °), we find the true height of the dust torus to be just under 1 ly. This leads us to the conclusione that the torus in the Circinus galaxy is relatively thin, the ratio of height to diameter here is about h/d � 0.25. In comparison, the relative thickness in NGC 1068 is h/d � 0.6. This finding is in excellent agreement with the observation that the ionization cone of the Circinus galaxy has a much wider opening angle than that of NGC 1068 (comp. Fig. II.5.9 to Fig. II.5.1b). The previous Midi-observations of the two nearest Seyfert II galaxies thus strongly confirm the picture of a central dust torus preventing a direct view of the accretion disk. In the future, comparison with high-resolution radio maps and millimeter observations with alMa will enable us to study in more detail how the gas reservoir within the torus flows inwards, thus »feeding« the accretion disk. Interferometric Observations of the Nucleus of the Radio Galaxy Centaurus A At a distance of only 12 million ly, Centaurus A is the nearest radio galaxy. We have also observed it with Midi. This data shows the mid-infrared emission to be dominated by an unresolved point source. Its diameter is apparently smaller than 0.6 ly. From comparison with observations at radio- and millimeter-wavelengths, we conclude that this emission does not originate from warm dust, but from synchrotron radiation of high-energy electrons spiraling in a magnetic field of 0.3 Gauß (Fig. II.5.10). We will not �
go into the details of this source here, but only state that we found no evidence of the presence of a central, AGN heated dust distribution in Centaurus A. Obviously there is a class of AGN which has no dust torus. MIDI Observations of More Distant and Fainter Active Nuclei In 2005 we also succeeded in observing the Seyfert 1 galaxies NGC 3783 and Markarian 1239 as well as the Seyfert 2 galaxy MCG-5-23-16 with MIDI. This is remarkable insofar as these sources are below the previously assumed brightness limit of the instrument (10 �m flux from the nucleus � 1 Jy). This shows that MIDI is also able to observe sources in the range of 0.5 Jy without stabilization of the fringe pattern with the help of the planned fringe tracker FINITO (which will operate at about 2 �m, but is not in operation yet). This encouraging news extends our list of possible extragalactic targets for MIDI from three sources (NGC 1068, Circinus, Centaurus A) to at least one dozen. Based on the larger distance, the results obtained so far for the three sources mentioned above indicate that these cannot be resolved with the rather compact telescope combinations of the VLTI (Fig. II.5.2). The diameter of the expected dust torus is smaller than 10 mas. In the next step we will choose telescope combinations with larger separations. In fact, in order to fully prove the unified scheme, it is crucial to not only show that dust tori exist in Seyfert 2 galaxies. Evidence of similar tori in Seyfert 1 galaxies is just as important. Only this would prove Fig. II.5.10: MIDI measurements of the nucleus of Centaurus A agree well with the observed spectrum of the nonthermal synchrotron radiation of this radio galaxy. Open circles: observed flux, full dots: corrected for foreground absorption. Flux [Hz Jy] 10 13 10 12 10 11 10 10 10 9 10 9 10 10 10 11 II.5 Dust Tori in Active Galactic Nuclei 37 the gas and dust reservoir within the torus to be essential for the high – compared to the mass of the black hole – mass-inflow-rate and the resulting high luminosities of the Seyfert nuclei. Summary Even in its first three years of operation at the VLTI, MIDI has demonstrated that interferometric observations in the mid-infrared range allow important insights into the processes within active galactic nuclei. Direct evidence of dust tori in Seyfert 2 galaxies not only confirms the unified scheme, but for the first time also opens up the opportunity to study the gas reservoir that seems to be responsible for the high luminosity of Seyfert galaxies and their big brothers, the quasars. First results on the radio galaxy Centaurus A also allow us to work out the differences between Seyfert 1 galaxies (usually showing very weak radio emission) and radio galaxies. We are confident that we will also be able to detect the »missing link«, the tori in Seyfert 1 galaxies, with MIDI in the near future– or to disprove this theory. Thus the end of the first stage on the path to directly observing the physical processes in the center of active galactic nuclei may soon be reached. MIDI is paving the way towards a new era of extragalactic astronomy with interferometric techniques. (Klaus Meisenheimer, Konrad Tristram, Marc Schartmann, Sebastian Wolf, Thomas Henning, Hubert Klahr. Participating institutes: Landessternwarte Heidelberg; Leiden Observatory) 10 12 Frequency [Hz] Observations by MIDI 10 13 10 14
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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
Page 36 and 37: 34 II. Highlights cretion disk, one
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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Page 52 and 53: 50 III. Selected Research Areas III
Page 54 and 55: 52 III. Scientific Work Fig. III.1.
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88 IV. Instrumental Development All
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92 IV. Instrumental Development The
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110 V. People and Events 1� 10�
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112 V. People and Events V.2 Open H
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116 V. People and Events presented.
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118 V. People and Events The IMPRS
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136 V. People and Events Lemke: I w
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140 V. People and Events V.14 Where
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142 V. People and Events against sp
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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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