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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - DUST-IN-THE-WIND (Dust in the wind â€” a new paradigm for inflow and outflow structures around supermassive black holes)

Teaser

Summary

Active galactic nuclei (AGN) represent the active growing phases of supermassive black holes. For the first time, we are able to resolve the dusty gas on parsec scales and directly test our standard picture of these objects. While this â€œunification schemeâ€ relates the parsec-scale IR emission with a geometrically-thick disk, I have recently found that the bulk of the dust emission comes from the polar region of the alleged disk where gas is blown out from the vicinity of the black hole. Along with these polar features, the compactness of the dust distribution seems to depend on the accretion state of the black hole. Neither of these findings have been predicted by current models and lack a physical explanation.

To explain the new observations, I proposed a revision to the AGN unification scheme that involves a dusty wind driven by radiation pressure. Depending on their masses, velocities, and frequency, such dusty winds might play a major role in self-regulating AGN activity and, thus, impact the interplay between host and black hole evolution. However, as of now we do not know if these winds are ubiquitous in AGN and how they would work physically. Upon completion of the research program, I want to

â€¢ characterise the pc-scale mass distribution, its kinematics, and the connection to the accretion state of the AGN,
â€¢ have a physical explanation of the dusty wind features and constrain their impact on the AGN environment, and
â€¢ have established dust parallax distances to several nearby AGN, as a multi-disciplinary application of the constraints on the dust distribution.

For that, I will combine the highest angular resolution observations in the IR and sub-mm to create the first pc-scale intensity, velocity, and density maps of a sample of 11 AGN. I will develop a new model that combines hydrodynamic simulations with an efficient treatment of radiative transfer to simulate dusty winds. Finally, direct distances to 12 AGN with a combined 3% precision will be measured.

Work performed

Significant progress has been made on both the observational as well as the theoretical side. We have acquired a large amount of observations on the highest angular resolution telescopes in the infrared and sub-mm to probe the dusty regions around the supermassive black holes. As we have discovered more AGN with dusty winds, it is obvious now that those feature are ubiquitous and need to be incorporated in the paradigm of AGN unification. To this effect, we developed a new 3D radiative transfer model that takes these dusty winds into account and successfully modelled the new observations. The model grid has been made available to the scientific community for general use.

On the theoretical front, we have developed a new 3D radiative hydrodynamical model of the dusty gas around supermassive black holes. The simulations produce a strong dusty wind driven by the radiation pressure close to the AGN. While we are still missing one physical ingredient (the radiation force exerted by the emission from the medium itself), this shows that the principle of radiation driving a dusty wind as originally hypothesised does work.

Finally, we have significantly expanded our efforts to use AGN in cosmology. Aside from determining the distances to 12 AGN directly, we will also attempt to utilise AGN time lags in a similar way as supernovae are currently being used -- i.e. as standard candles. For that, we initiated a 3-year survey of part of the sky in the optical and near-infrared to monitor about 500 AGN and determine their time lags. These will be used as a proxy for the AGN luminosity on a Hubble diagram to infer cosmological parameters, such as the dark matter energy density or the dark energy equation-of-state.

Final results

The following lists some selected highlights of the ongoing work based on current achievements:

* The observation of the new GRAVITY instrument taken by the GRAVITY AGN team (the PI is part of the team) spatially resolved, for the first time, the fast-rotating gas around the black hole inside of the dusty medium studied in this work. These results have been published in Nature, accompanied by a press release. It confirms that the gas is orderly rotating around the black hole, which makes it possible to kinematically determine the masses of supermassive black holes.

* The upcoming MATISSE observations are expected to make a similar impact as the GRAVITY data.

* Our new 3D radiative hydrodynamical model breaks new ground in the field as it includes several new methods to implement the physics. We are using, for the first time, the entire AGN spectrum to calculate how the radiative processes affect the dusty environment. Moreover, our chosen method allows for resolving the very thin layer of gas where radiation pressure launches a wind.

* The possibility to establish AGN as standardisable candles for cosmology open a new way to independently constrain cosmological parameters and test for biases in the current cosmological probes.