ESO VLT: The dusty heart of Circinus, an active galaxy

Nuclear region of the Circinus galaxy. 

The right image shows the inner 1000 light years of the Circinus galaxy. 

Blinding light and gaseous material are ejected by the active nucleus (located at the black box). 

They escape only along a conical region towards the northwest (upper right part of the image), leading to the white V-shaped structure in this image. 

Along other directions, the nuclear region is hidden by dense gas and dust.

This obscuring dust has now been investigated with unprecedented detail with the ESO Very Large Telescope (VLT) Interferometer. 

The false-colour model image on the left shows the dust emission and corresponds to the region marked by the black box in the right image.

The emission comes from a relatively thin, disk-like structure (white) as well as dust elongated perpendicular to it. 

The disk is also seen by water emission (red-green-blue line). 

The dust emission is more absorbed towards the southeast (bottom left) than the northwest (top right), illustrated by the change from violet to green colours. 

Credit: Konrad Tristram; Right: NASA HST, STScI.

An international research team led by Konrad Tristram from the Max-Planck-Institute for Radio Astronomy in Bonn, Germany, obtained the most detailed view so far of the warm dust in the environment of a supermassive black hole in an active galaxy.

Konrad Tristram

The observations of the Circinus galaxy show, for the first time, that the dust directly illuminated by the central engine of the active galaxy is located in two distinct components: an inner warped disk and a surrounding larger distribution of dust.

Most likely, the larger component is responsible for most of the obscuration of the inner regions close to the supermassive black hole.

Such a configuration is significantly more complex than the simple dusty doughnut, which has been favoured for the last few decades.

The results are published in the current issue of Astronomy & Astrophysics.

In active galactic nuclei, enormous amounts of energy are released due to the feeding of the supermassive black hole in the centre of the galaxy.

Such black holes have masses of a million or billion times the mass of the sun.

The matter spiralling in onto the black hole becomes so hot and luminous that it outshines its entire galaxy with billions of stars. The huge amounts of energy released also affect the surrounding galaxy.

Active galactic nuclei are therefore thought to play an important role in the formation and evolution of galaxies and hence in the formation of the universe as presently seen.

Using the MIDI instrument at the ESO Very Large Telescope (VLT) Interferometer in the Atacama Desert of Chile, the research team obtained an unprecedented clear view of the warm dust in the nucleus of the Circinus galaxy.

At a distance of only 13 million light years, the Circinus galaxy contains one of the closest and brightest active galactic nuclei.

"We obtained at least twice the amount of interferometric data than for any other galaxy", proudly reports Konrad Tristram from the Max-Planck-Institute for Radio Astronomy (MPIfR), the lead author of the paper.

"Our observations make the Circinus galaxy by far the best observed extragalactic source in optical and infrared interferometry."

By combining the light of two telescopes, the interferometric observations increase the resolution to that of a telescope of 92 meters in diameter.

In the case of the Circinus galaxy, the scientists could, for the first time, show that the emission of the nuclear dust comes from two distinct components, an inner disk-like component and an extended component significantly elongated in polar direction.

The dust disk in the Circinus galaxy has a size of about 3 light years and agrees well with a warped molecular disk revealed by water emission.

More information: "The Dusty Torus in the Circinus Galaxy: A Dense Disk and the Torus Funnel," K. R. W. Tristram, L. Burtscher, W. Jaffe, K. Meisenheimer, S. F. Hönig, M. Kishimoto, M. Schartmann, and G. Weigelt, 2014, Astronomy & Astrophysics. dx.doi.org/10.1051/0004-6361/201322698; Preprint: arxiv.org/abs/1312.4534