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

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

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.

Active Galactic Nuclei Some other observations: AGN are very bright in a wide range of the EM spectrum: luminocities can get up to L sun 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)?

Active Galactic Nuclei Building blocks Many models of AGN predict existance of a Central Engine: supermassive Black Hole ( M sun ) 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

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.

The building blocks of AGN 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.

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)

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:

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).

Dusty Tori First indirect measurements Antonucci 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 measurements Jaffe 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]

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

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.

NGC1068

VLTI / MIDI

2 Gaussian model

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

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