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The Dusty Torus of NGC1068

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burton
19 diapositives · 352 Views · Sep 15, 2014

This research project focuses on the dusty torus surrounding the active galactic nucleus (AGN) of NGC 1068, utilizing measurements obtained from the VLTI's MIDI instrument. The study aims to validate a two-component model of the torus, enhancing our understanding of its structure, including its shape and temperature distribution. By analyzing the ratio of Seyfert I to Seyfert II galaxies, we will estimate the torus height and explore potential stability issues. This work contributes to the unification model of AGNs, revealing the intricate dynamics of these cosmic phenomena.

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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