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The Dusty Torus of NGC1068

Literature Study for the Bachelor Research Project:. The Dusty Torus of NGC1068. Bas Nefs Maarten Zwetsloot. Overview. Active Galactic Nuclei Dusti Tori NGC1068 MIDI Measurements with the VLTI Our Research Project. Active Galactic Nuclei.

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The Dusty Torus of NGC1068

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  1. Literature Study for the Bachelor Research Project: The Dusty Torus of NGC1068 Bas Nefs Maarten Zwetsloot

  2. Overview • Active Galactic Nuclei • Dusti Tori • NGC1068 • MIDI Measurements with the VLTI • Our Research Project

  3. Active Galactic Nuclei • 1943 – Astronomer Carl Seyfert no-tices that certain nearby spiral gala-xies have very bright almost starlike nuclei. • First Active Nuclei to be recognized. • Spectra of these galaxies show strong and often broad emis- sion lines.

  4. Active Galactic Nuclei • Some other observations: • AGN are very bright in a wide range of the EM spectrum: luminocities can get up to 1010-1013 Lsun and higher. • They come in a wide variety of types with slightly different properties – the 'AGN zoo' • These nuclei are variable in time, periods from hours up to months → objects are really small, in the pc size scale. • Nonstellar energy source(s)?

  5. Active Galactic Nuclei Building blocks Many models of AGN predict existance of a Central Engine: supermassive Black Hole (106 - 109 Msun) at the very centres of galaxies. Surrounding gas clouds fall in → flat accretion disk of hot gas Release of gravitational energy → high energy ionizing radiation

  6. Active Galactic Nuclei • Building blocks (continued) From spectroscophy: Large regions of gas clouds surrounding the central engine ionised by radiation. BLR (Broad Line Regions) -- strong and broad emission lines -- large Doppler broadening → large range in velocities due to rotation and turbulent motions NLR (Narrow Line Regions) -- narrow lines -- lower velocities of gas and lower electron densities.

  7. Active Galactic Nuclei The building blocks of AGN

  8. Active Galactic Nuclei The unified model(Antonucci 1993): no more zoology Properties and evolution of different kinds of AGN depend solely on orientation (different viewing angles) and black hole mass. Jets Dusty torus Ionisation cones -- torus collimates the radiation from the central engine in coneshaped regions.

  9. Active Galactic Nuclei The Zoo of AGN *Seyfert Galaxies At small distances and at low end of luminocity range (e.g. NGC1068 at 14.4 Mpc)

  10. Active Galactic Nuclei Seyfert Galaxies 2 'flavours' depending on the viewing angle: Seyfert I Seyfert II The torus is viewed face-on: BLR is well exposed so broad and narrow lines in spectrum. Edge-on view on torus: BLR obscured by torus In between:

  11. Dusty Tori • What are they?Dusty tori are large structures of dust (~100 pc) around the central engines of AGN. They were ‘invented’ by astronomers for the unification of the Seyfert I and Seyfert II galaxies.These dust structures should have some sort of doughnut shape. When viewed face-on, the broad line region is clearly visible (type I) while this is not the case when viewed edge-on (type II).

  12. Dusty Tori • First indirect measurementsAntonucci and Miller (1985) discovered broad line features in the polarized UV-spectrum of a Seyfert II galaxy. This indicates this galaxy contains a hidden type I nucleus. The light from the nucleus leaves the dusty torus through the hole and is scattered (and polarized) into our viewing direction. [pic] • First direct measurementsJaffe et al. (2003) used the newly installed Mid-infrared instrument (MIDI) at the VLTI to obtain measurements of the core of NGC1068 with mas-resolution. By fitting parameters of a ‘2 Gaussian’ model they found an inner hot component (>800 K) and a warm component (350 K). [pic]

  13. Dusty Tori What does a torus explain? *Hidden Broad Line Regions *Ionization cones *Ratio of type2/type1 AGNs ~ 4:1 • SpectrumDust, heated by the central engine, emitting BB-radiation. [pics]

  14. Dusty Tori • Problems • By looking at the ratio of Seyfert I and Seyfert II galaxies we can estimate a mean height for the dusty tori. The height we find is to large for the dust structures to be stable.

  15. NGC1068

  16. VLTI / MIDI

  17. 2 Gaussian model

  18. Research Project What do we hope to achieve in this BP? *Checking the validity of a simple 2 component model with new interferometric observations from VLTI *Introducing differential phase in torus modelling *If given enough time: extending the modelling to more complex torus geometries, like a warped disk or clum- py torus *Changing dust properties

  19. Coverage of the (u,v)-plane needs to be increased -> more accurate modelling for different projected baselines

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