Active Galactic Nuclei: accretion and feedback across the mass scale with eROSITA and LOFAR

Igo, Zsofi (2026): Active Galactic Nuclei: accretion and feedback across the mass scale with eROSITA and LOFAR. Dissertation, LMU München: Fakultät für Physik

Abstract

Supermassive black holes (SMBHs) are found at the centre of almost every massive galaxy. Around 1 − 10% of SMBHs are accreting matter from their surroundings, making them _active_ galactic nuclei (AGN). AGN are some of the most luminous, persistent emitters of radiative and kinetic energy in the entire Universe. This energy, released across the electromagnetic spectrum from radio to X-ray wavelengths and through powerful outflows, can significantly impact the host galaxy, in a process called 'AGN feedback'. AGN feedback occurs in various forms, such as wide-angle winds or collimated jets launched from the vicinity of the black hole that propagate to larger scales, displacing or heating gas and dust, and thereby suppressing star formation. While AGN are a crucial ingredient to understanding galaxy evolution, it is still unclear how the accretion energy coming in and the feedback energy coming out depend on AGN and host galaxy properties, as well as how they vary across cosmic time. As such, I begin this Thesis by tackling the question of how jetted feedback emission depends on the stellar mass of the galaxy. AGN jets primarily emit via synchrotron radiation, observable at radio wavelengths. Therefore, we can use radio observatories here on Earth, such as the Low Frequency Array (LOFAR), to probe large samples of jetted AGN. I compile a new statistical sample of 764 LOFAR radio AGN at low redshift (z < 0.4) and calculate for the first time the fraction of galaxies hosting such radio AGN (i.e. the radio AGN incidence) as a function of specific black hole kinetic power, λJet, a measure of how powerful the jets are compared to the mass of the galaxy (a proxy for the mass of the black hole). I find that the incidence of radio AGN shows a mass-dependence, whereby higher mass galaxies are more likely to host a radio AGN at all values of λJet. This is interesting as previous work investigating the incidence of X-ray AGN find that the mechanisms responsible for triggering and fuelling AGN across all massive galaxies are mass-invariant (to first order). Therefore, it is curious that jetted feedback, supposedly fuelled by the accretion process, behaves differently. I try to reconcile this by analysing the coupling between the accretion disk and jet in AGN using the statistical incidence distributions of X-ray and radio AGN. In addition to the mass-dependence, the radio AGN incidence shows a striking variation for different radio AGN morphologies. Compact radio AGN show a steep power-law-like incidence, meaning that they dominate at lower jet powers and drop out rapidly at higher jet powers. In contrast, complex radio AGN, those with extended, possible double-lobed morphologies, show a flatter incidence distribution with a much stronger mass-dependence, indicating that they progressively dominate for higher stellar mass and λJet values. Thanks to the well-characterised, complete, spectroscopic radio AGN sample, I have detailed knowledge of the host galaxy mass, the jet power of a given radio AGN and how often this radio AGN of a given jet power populates a galaxy of a given mass. Capitalising on these three factors, I derive the average jet power of the population of massive galaxies at low redshift and find that the kinetic feedback from radio AGN dominates over any plausible inventory of radiatively-driven feedback, such as the aforementioned winds. Interestingly, it is the compact radio AGN that dominate this global kinetic energy budget for all but the most massive galaxies. I also compare this average injected jet energy against the galaxy and larger-scale dark matter halo binding energy and against the total thermal energy of the host gas within the halos. I show that although radio AGN, be it compact or complex, do not have enough energy to fully disrupt the global gas distribution of massive galaxies, they provide a significant source of heat that can impact the local thermodynamical balance in even the cores of the most massive clusters (groups of galaxies) in our local Universe. Finally, I probe the details of the accretion process in an as-of-yet unexplored parameter space of low-mass galaxies at low redshift. This has been made possible by the recent advancements in deep, multi-wavelength all-sky surveys. In particular, this Thesis makes use of the deepest four-pass eROSITA All Sky Survey (eRASS:4), in combination with optical imaging from the 10th Data Release of the DESI Legacy Imaging Survey (LS10), to investigate the incidence of X-ray AGN as a function of specific black hole radiative power, λEdd. This is a complementary mass-scaled power indicator to λJet. Starting from an optically selected parent sample from LS10 of over 5 million galaxies across the mass scale, I find 874 X-ray AGN in low-mass galaxies (log M∗/M⊙ ≤ 10), more than 600 of them newly discovered. Thanks to a Bayesian framework that makes use of the X-ray information from all parent sample galaxies, I place the tightest constraints on the specific accretion rate distributions (at least at the high accretion rate end), to date, revealing second-order mass-dependent properties. Then, I derive the cumulative AGN fraction as a function of stellar mass by integrating this distribution. Interestingly, I find a peak in this cumulative AGN fraction around log M∗/M⊙ ∼ 10 − 10.5, for moderately- and highly-accreting X-ray AGN, potentially highlighting a decrease in the efficiency of AGN fuelling at both very low and very high masses. Additionally, the peak aligns relatively well with the location where the star-formation efficiency as a function of halo mass is maximal, potentially pointing to a common physical condition that is responsible for AGN accretion and star-formation. Future detailed X-ray spectral-timing analysis on this new sample of X-ray AGN could reveal unique insights about the details of accretion and feedback in the low-mass regime.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Active Galactic Nuclei (AGN), accretion, AGN feedback, AGN incidence, eROSITA, LOFAR, X-ray, radio, multi-wavelength, low-mass galaxies, dwarf galaxies
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 2. Februar 2026
• 1. Bericht­erstatter:in: Nandra, Kirpal