Active Galactic Nuclei

Our AGN projects focus on the properties of the gas, dust, and stars close to the central black hole in active galaxies. Our primary aim is to understand the geometrical and kinematical structure of gas in the so-called Broad-Line Region and whether the hottest gas and dust we see is related to the obscuring dusty structure that, from some viewing angles, hides the accretion disk and BLR.

We also want to learn more about ionized and molecular outflows by studying them near their launching sites. This AGN feedback can drive gas out of the galaxy, and so we aim to connect these small-scale phenomena to the large-scale outflows seen in more luminous distant AGN. A further aspect of our work is to understand the role of star formation in the central tens of parsecs – how old it is, and how intense – and what impact it has on the further flow of gas to the inner few parsecs.

To reach the highest spatial resolution needed, we make use of near-infrared interferometry with GRAVITY (and soon GRAVITY+) at the Very Large Telescope Interferometer that allows us to spatially resolve the high-velocity clouds comprising the Broad-Line Region and the very hot dust at the sublimation radius.

For studies on larger scales in the circumnuclear region, we frequently use adaptive optics at the Very Large Telescope with near infrared integral field spectrometers, such as SINFONI and the upcoming ERIS. For higher spectral resolution, and to probe the stellar populations, we make use of spectra covering wide wavelength ranges from the UV to the near-infrared as afforded by the echelle spectrograph XSHOOTER. Finally, to study the cold molecular gas NOEMA at IRAM in France as well as APEX and ALMA in Chile provide complementary data on many molecular lines at millimeter and submillimeter wavelengths.