Anne-Kathrin Baczko, Astrophysicist

Active Galactic Nuclei - AGN

ESO CenA — The AGN in Cen A with its large scale jets. Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A. Weiss et al. (Submillimetre); NASA/CXC/CfA/R. Kraft et al. (X-ray).

Active Galaxies are among the most energetic objects in the universe. Their innermost center, the Active Galactic Nucleus (AGN) has the potential to over-shine the whole stellar population. Accretion onto a supermassive black hole is the most conclusive physical process to explain their huge emission over the whole electro-magnetic spectrum. A subset of these galaxies is characterized by strongly collimated, relativistic outflows, called jets. I am fascinated by these sources since my undergraduate studies and focus my research on the innermost parsecs around the central engine to understand the physical processes behind jet acceleration and collimation.

Jets in AGN

My colleagues and me are studying AGN jets from their formation around the central supermassive black hole towards their outer edges far away from the central engine. We want to understand how these jets are produced, accelerated towards relativistic speeds, and how they remain collimated until distances far beyond the size of the galaxy itself. In order to solve these puzzles we observe AGN jets at radio wavelengths employing the technique of Very Long Baseline Interferometry (VLBI). By combining these observations with numerical simulations (Fromm et al. 2019, A&A 629, A4) we test current physical models of jet formation and improve the accuracy of the simulations.

The twin-jet in NGC 1052 at highest angular resolution

NGC 1052 first GMVA observation — Curious? Read more about it in our press release: Twin jets pinpoint the heart of an active galaxy

The galaxy NGC 1052 hosts an AGN with a two-sided jet emanating to the East and the West. With a redshift of 0.005 and a distance of 20 Mpc it is one of the very few nearby radio galaxies that allows us to study the innermost jet forming regions with the technique of VLBI at scales as small as 200 Schwarzschild radii. We observed the source over multiple frequencies from 1.4 GHz to 86 GHz with several VLBI facilities, including the GMVA, RadioAstron, the EVN, and the VLBA.

This figure shows the source as observed at 86 GHz with the GMVA in 2004. We found an unresolved core in-between the two symmetric, faint jets, which allowed us to estimate the strength of the magnetic field close to the central engine.

The expansion of the jets in NGC1052

Figure 10 in Baczko et al. 2022, A&A 658, A119

We observed NGC 1052 over multiple frequencies from 1.4 GHz to 43 GHz with RadioAstron and the VLBA in 2016 and 2017. In our study (Baczko et al. 2022, A&A 658, A119) we describe our findings of an exceptionally straight and strongly collimated jet pair.

This figure shows the jet width with distance from the center for the approaching, eastern jet and the receding, western jet. We found a change from a cylindrical to a conical geometry at 10000 Schwarzschild radii (see Fig. 3). This is in contrast to observational results based on blazars which reveal a change from a parabolic to conical expansion. While the change from parabolic to conical is consistent with a change from a magnetically to a kinetically dominated jet, a cylindrical profile challenges this picture. One process leading to this strong collimation is confinement through the surrounding material, e.g. the dense plasma torus which covers the innermost 2 mas in NGC 1052. On the other hand scattering in the surrounding torus or accretion disc winds might mimic a cylindrical profile. Using stacked images the jet widths at 43 GHz are significantly smaller compared to 15 and 22 GHz at distances closer than 3000 Schwarzschild radii to the central engine. This suggests differential expansion inside the acceleration zone of the jet. Following my results I successfully proposed for highly competitive multi-year GMVA observations of NGC 1052 which are currently ongoing and will provide a unique chance to study possible acceleration within the magnetically dominated regime in a double-sided jet. These observation might provide the missing link to understanding the complex expansion profile.

Research Unit "Relativistic Jets in Active Galaxies"

Learn more about the research unit: FOR 5195

I am an external member of the DFG research unit FOR 5195 led by the JMU Würzburg. To answer the most fundamental questions about the composition, formation, collimation, and dissipation of extragalactic jets this research unit brings together experts in observations, modelling, and theory of AGN jets.

Within FOR 5195 I frequently collaborate with Dr. Christian Fromm (JMU Würzburg) who is an expert on general relativity MHD simulations of AGN jets. To model the jets in NGC 1052 my observational results served as input for relativistic MHD simulations (Fromm et al. 2019, A&A 629, A4). To find the most likely physical parameters we used a nonlinear optimization which is guided by observed properties, such as the overall source structure. These numerical simulations suggest that the jets in NGC 1052 can best be modeled by a slightly overpressured jet.

M2FINDERS

I am collaborator of the M2FINDERS (Mapping Magnetic Fields with INterferometry Down to Event hoRizon Scales) project awarded by the ERC to Anton Zensus. Its goal is to develop technical and radio astronomical methods to map magnetic fields at distances smaller than 1000 gravitational radii to the SMBH.

To achieve this ambitious goal the project will bring together experts from three main areas of VLBI research:

Polarisation VLBI imaging
VLBI interferometry techniques
Theoretical expectations of the magnetic field near the event horizon.

The Event Horizon Telescope Collaboration

M87 EHT black hole shadow — The black hole shadow in M87 (Cite: EHTC et al. 2024, A&A 681,79 )

During my PhD I joined the Event Horizon Telescope Collaboration (EHTC). Thanks to the superb resolution of the EHT and a tremendous effort our collaboration published the first image of the shadow of the black hole in the center of the AGN M 87 in 2019. Find out more in our most recent publication: EHTC et al. 2024, A&A 681,79.

I am currently leading an official EHT project on multi-wavelength VLBI observations of NGC 1052 focusing on the continuum spectrum of the innermost central component.

The increasing ability to include ALMA to global VLBI arrays offers promising prospects for future combined EHT plus lower frequency VLBI+ALMA observations of southern AGN. Learn more about the EHT and the collaboration: Event Horizon Telescope.