Towards a comprehensive understanding of the interstellar medium in the extreme environment of Active Galactic Nuclei

• Applicant: Dr. Leonard Burtscher
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263101211

A fundamental role is attributed to supermassive black holes in the evolution of galaxies. But theoretical models trying to reproduce the relation between black hole mass and stellar velocity dispersion and other relations, have to make broad assumptions about the physical processes involved, and the prescriptions used are poorly constrained. The implementation of AGN feeding and feedback in models remains simplistic because observations have focussed on the question of where the inflowing material originates - mergers versus secular evolution - and on integrated galaxy properties.In contrast, there is now an increasing realisation that AGN activity may be flickering on timescales as short as a few million years and that the feeding must therefore be governed by processes on the 10 - 100 pc scale. Our popular evolutionary starburst model describes AGN activity as a time-sequence where (1) cold gas inflows lead to a nuclear starburst that soon (2) stirs the ISM (via exploding type II supernovae) and prevents the gas from cooling. Only after this violent phase has ended (3), do stellar winds from evolved stars inject new mass into the nuclear ISM. The angular momentum of the ejected material dissipates in collisions and a stable accretion flow forms - the AGN lights up. Initial observational and theoretical studies have suggested that such a connection could exist.Yet these nuclear processes have not been systematically studied, since the detailed research necessary was focused on individual well-known galaxies instead of the population as a whole. To remedy this, we will address the physical properties of the ISM in a complete sample of the most powerful local AGNs and compare them with an equally large sample of inactive galaxies, carefully matched in distance, mass, inclination and large-scale galaxy properties (Hubble type, prevalence of bar).In order to gather a comprehensive understanding of the feeding and feedback of AGNs we have already begun observing the 20 most luminous local AGNs as well as the control sample. Using VLT/SINFONI integral field spectroscopy in the H+K bands we will determine the dynamics of the stars and gas; high resolution and high quality VLT/XSHOOTER spectroscopy from the UV to the NIR will give us unprecedented leverage to determine the stellar populations and infer their impact on the ISM. Finally, observations of multiple molecular gas transitions of several species will allow us to determine directly the physical conditions of the gas in both active and inactive nuclei.Our novel approach brings together the multi-scale and multi-wavelength observational evidence. In combination with our hydrodynamical models, that are ready to be used, it will allow us to establish a solid statistical basis for understanding the differences in the physical conditions of the ISM in AGNs and inactive galaxies on the scales that are directly relevant to accretion onto the central supermassive black hole.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1573: Physics of the Interstellar Medium
• International Connection: Netherlands
• Participating Persons: Dr. Richard Davies; Dr. Marc Schartmann