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The life cycle of starbursting circumnuclear discs

 

High-resolution observations from the submm to the optical wavelength regime resolve the central few 100 pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, inflows and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of 


galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc’s subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100 pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales.

 

 

 

Radiative transfer modelling of AGN tori


Active Galactic Nuclei (AGN) are thought to be enshrouded by geometrically and optically thick toroidal dust distributions, the so-called molecular tori. We derive observable properties for a self-consistent model of such toroidal gas and dust distributions, where the geometrical thickness is achieved and maintained with the help of X-ray heating and radiation pressure due to the central engine (Wada et al., 2012). We simulate spectral energy distributions (SEDs) and images with the help of dust continuum radiative transfer calculations with RADMC-3D (Dullemond et al., 2012). This results - for the first time - in time-resolved SEDs and images for a physical model of the central obscurer. We find that temporal changes are mostly visible at shorter wavelengths, close to the combined peak of the dust opacity -- which follows a loal dust extinction law -- as well as the central source spectrum and are caused by variations in the column densities of the generated outflow. Because of the three-component morphology of the hydrodynamical models -- a thin disc with high-density filaments (the remainder of the initial condition and determined by the inflow from larger scales), a surrounding fluffy component (the obscurer) and a low-density outflow along the rotation axis - we find dramatic differences depending on the observed wavelength: whereas the mid-infrared images are dominated by the elongated appearance of the outflow cone, the long wavelength emission is mainly given by the cold and dense disc component. Overall, we find good agreement with observed characteristics, especially for those models, which show clear outflow cones in combination with a geometrically thick distribution of gas and dust, as well as a geometrically thin, but high column density disc in the equatorial plane. 

 

by Andreas Burkert

Evolution of the Galactic Centre Cloud G2



We investigate the origin, structure and evolution of the small gas cloud, G2, which is on an orbit almost straight into the Galactic central supermassive black hole (Gillessen et al., 2012). The movie shows the evolution of the cloud in an idealised hot atmosphere, using the hydrodynamics code PLUTO. With the help of such simulations and analytical calculations, we find that G2 is a sensitive probe of the hot accretion zone of Sgr A* and we can show that the observed structure and evolution of G2 can be well reproduced if it formed in pressure equilibrium with the surrounding in 1995 at a distance from the SMBH of 7.6e16 cm. Another possibility is that G2 is the head of a larger, shell-like structure that formed at apocenter. Our numerical simulations show that this scenario explains not only G2's observed kinematical and geometrical properties but also the observations of a low surface brightness gas tail that trails the cloud. In 2013, while passing the SMBH G2 will break up into a string of droplets that within the next 30 years mix with the surrounding hot gas and trigger cycles of AGN activity. 

Click on the image to see the ESO press release movie (Credit: ESO/MPE/M.Schartmann/L.Calçada)!

 

 

Highlights

Ausgerechnet! Unser Universum
Gas perturbations reveal protoplanets
  The central parsecs of the low-luminosity active galaxy NGC 1052: evidence for a truncated accretion disc
   A UNIQUE DATA CENTRE FOR COSMOLOGICAL SIMULATIONS
Clusters of Small Clumps in High-Redshift Disk Galaxies
Magneticum Pathfinder: The evolution of the universe in an unmatched extend
The complex Interplay between Spin, Mass, and Morphology in Galaxies The complex Interplay between Spin, Mass, and Morphology in Galaxies
Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs) Magneticum sheds new light on recently discovered Fast Radio Bursts (FRBs)
A Disk-Disk Major Merger Event in a Cosmological Hydrodynamical Zoom-Simulation A Disk-Disk Major Merger Event in a  Cosmological Hydrodynamical Zoom-Simulation
The formation of filamentary bundles in turbulent molecular
  clouds The formation of filamentary bundles in turbulent molecular clouds
G2 modelled as a mass-losing source of gas G2 modelled as a mass-losing source of gas
Supernova-driven galactic winds Supernova-driven galactic winds
Dark-halo spheroid conspiracy The Dark Halo-Spheroid Conspiracy and the Origin of Elliptical Galaxies
Julius Donnert receives PhD award of AG Phd Award 2012 of the Astronomische Gesellschaft
CAST group outing 2012 CAST group outing 2012
Evolution of the Galactic Centre Cloud G2 Evolution of the Galactic Centre Cloud G2
Dr.Hanna Kotarba receives the Universe PhD award Universe Cluster PhD Thesis Award 2011
Evolution of Molecular Clouds in Spiral Galaxies Evolution of Molecular Clouds in Spiral Galaxies by Clare Dobbs
Globular Clusters vs. Black Hole Mass Relation Globular Clusters Black Hole Correlation by Andreas Burkert
Cosmological Resimulations Cosmological Resimulations by Ludwig Oser
Star Formation in the Galactic Centre Star Formation in the Galactic Centre by Christian Alig
A New Model for the Antennae Galaxies A New Model for the Antennae Galaxies by Simon Karl
Simulating the Bullet Cluster Simulating the Bullet Cluster by Chiara Mastropietro
Triggered Star Formation Triggered Star Formation by Matthias Gritschneder
The Mystery of Sedna The Mystery of Sedna by Hagen Schulte in den Bäumen
The Formation of Fossil Galaxy Groups The Formation of Fossil Galaxy Groups in the hierarchical Universe by Elena D'Onghia
Molecular Cloud Formation in Colliding Flows Molecular Cloud Formation in Colliding Flows by Fabian Heitsch
Planet-Disk Interaction Comparison of hydro codes on planet-disk interaction problem by Pawel Ciecielag
Galactic Orbits Orbital Structure of Galaxies in N-Body Simulations by Roland Jesseit