The Dusty Torus of NGC1068Literature 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 1010-1013 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 NucleiBuilding 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 gasRelease of gravitational energy→ high energy ionizing

radiation

Active Galactic Nuclei

• Building blocks (continued)

From spectroscophy:

Large regions of gas clouds surrounding the centralengine ionised by radiation.BLR (Broad Line Regions) -- strong and broademission lines -- large Doppler broadening→ large range in velocities due to rotation and turbulent

motionsNLR (Narrow Line Regions) -- narrow lines -- lower

velocities of gas and lower electron densities.

The building blocks of AGN

Active Galactic Nuclei

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 NucleiThe Zoo of AGN

*Seyfert Galaxies

At small distances and at low end of luminocity range (e.g. NGC1068 at 14.4 Mpc)

Active Galactic NucleiSeyfert 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 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]

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]

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