Dust in the wind — a new paradigm for inflow and outflow structures around supermassive black holes

Project Information

DUST-IN-THE-WIND

Grant agreement ID: 677117

DOI

10.3030/677117

Project closed

EC signature date 3 December 2015

Start date 1 May 2016

End date 30 September 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 475 171,00

EU contribution

€ 1 475 171,00

Coordinated by

UNIVERSITY OF SOUTHAMPTON
United Kingdom

Periodic Reporting for period 4 - DUST-IN-THE-WIND (Dust in the wind — a new paradigm for inflow and outflow structures around supermassive black holes)

Reporting period: 2020-11-01 to 2021-09-30

Summary of the context and overall objectives of the project

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 “unification scheme” 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 wanted to

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

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

(1) Characterisation of the pc-scale environment of the AGN: The primary goal was to establish the presence of dusty winds as a genuine feature in AGN. This has been achieved via a combination of VLT interferometry, single telescope and ALMA observations. While I originally relied on a specific new instrument (MATISSE), due to a delay plans needed to be changed. I have joined forces with the team building another interferometry instrument (GRAVITY). This included the first spatially resolved observations of the sub-parsec scale region of a quasar and the first reconstructed interferometric images of AGN in the infrared. In addition, I made use of the extended ESO science archive and we analysed archival data, both unpublished and previously published. Finally, a co-founded a team (GATOS) that undertook a survey of nearby AGN with ALMA in the sub-mm. As a result of these efforts, were were able to show that the obscuring structure around the AGN is dynamically and geometrically more complex than what may be expected from a single torus. We showed that dense, extended, geometrically thin disks are present in most of the Seyfert galaxies we observed and that they show some level of polar extended features in the dust continuum and molecular emission. With the archival data, we were able to show that the strength of polar features relative to the disks depends on Eddington ratio, as one would expect for a wind driven by radiation pressure.

(2) The physics of dusty wind features: To achieve this objective, advancements on the physical and radiative transfer modelling needed to be made. As part of the project, I revised my existing radiative transfer model of AGN to represent the configuration of a disk and polar wind. The model has been independently tested and been found to be overall the best to represent the infrared emission of AGN, especially in the mid- to high-luminosity regime where dusty winds are probably most common. The second, main part of this objective was building a new 3D radiation hydrodynamics code to simulate the parsec scale AGN environment and wind launching mechanisms. This required a huge effort, but resulted in a model that covers the widest dynamical range in all relevant parameters compared to other models and provides the resolution to resolve the wind launching mechanisms. We were able to show that dusty winds are a natural consequence of AGN and even if the AGN radiation pushes radially, will eventually result in polar extended infrared emission. We were also able to identify a mechanism that makes the winds and part of the accretion flow clumpy. Finally, I combined the bits of individual physics we learned from observations and simulations and proposed a full physical framework to explain observed phenomena, including predictions for the mass loss in dusty (molecular) winds due to radiation pressure on the dust.

(3) Dust parallax distances to AGN: This was the most challenging objective on the technical side. The original idea was to use an existing interferometric instrument at the VLTI (AMBER) and an established optical+infrared camera (SMARTS-ANDICAM). As AMBER suffered a calibration issue in the low-flux regime that could not be resolved, I used the new GRAVITY instrument instead with the team established for (1). Second, the SMARTS-ANDICAM camera broke about half way through the multi-year observing campaign without being replaced. As this inevitable meant that not the entire sample of AGN originally planned for would be covered, I reverted to extend the project from AGN as standard rulers to AGN as standard candles. For that, I established the VEILS public survey at the ESO 4m VISTA telescope. This survey uses the lag-luminosity relationship in AGN to use them in a similar way for cosmology as supernovae. The survey produced massive amounts of data that we are still in the process of analysing, with delays coming from temporary closure of the observatory due to COVID and staff changing jobs. In the end, we were able to use GRAVITY data and existing light curves to calculate direct distances to 5 AGN. However, the science prospects sparked interested beyond our group and is part of the science case for the new GRAVITY+ instrument that is currently being built.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

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. The GRAVITY observations of NGC1068 were used to produce the first reconstructed image of an AGN in the infrared at milliarcsecond resolution (GRAVITY collaboration 2020a,2021, Leftley et al. 2021). Our new 3D radiative hydrodynamical (3DRHD) 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 (Williamson, Hoenig & Venanzi 2019, 2020). We calculated geometrical distances to 5 AGN (GRAVITY collaboration 2020b, 2021). 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 (Hoenig et al. 2017). The 3D RHD model has been adapted to perform the first RHD simulations of supermassive black hole binary systems (Williamson, Bösch & Hoenig 2022). The project established a new paradigm for the parsec scale mass distribution around AGN, including a physical explanation for the various phenomena (Hoenig 2019).

Illustration (right) and 3D RHD simulations (left) of the parsec-scale environment of AGN