Title: AGN spin and jet direction and alignment with host galaxies
Supervisors: Prof. Dr. Joop Schaye and Dr. Filip Huško
Institution: University of Leiden
Abstract: Supermassive Black Holes (BH) are thought to affect their host galaxies through energy release as Active Galactic Nuclei (AGN feedback). In hydrodynamical simulations of galaxy formation, AGN feedback has been largely implemented as isotropic winds. The COLIBRE simulations, developed at Leiden University, use a hybrid model of AGN feedback that combines both isotropic winds and kinetic jets. In this thesis, we analyse simulations run using the hybrid AGN feedback model by looking at BH spin and jet alignments with the stellar angular momentum and the semi-minor axis of the host galaxy, both in 3D and in projection. We divide our analysis in two parts, one focusing on BH spin and one focusing on jets. For jets, we use a \((200 \,\mathrm{cMpc})^3\) box at \(\mathrm{\approx 10^7 \; M_{\odot}}\) resolution (m7) and a \((100 \,\mathrm{cMpc})^3\) box at \(\mathrm{\approx 10^6 \; M_{\odot}}\) resolution (m6), while for BH spin we use an additional \((50 \,\mathrm{cMpc})^3\) box at m6 resolution. We compare our results to an observational sample of AGN jets containing 3682 sources with LoTSS and FIRST radio emission, and SDSS optical emission. Black hole spin is well aligned with the stellar angular momentum of the host galaxy for intermediate-mass galaxies \((\mathrm{M_{\ast} \approx 10^{10}\; M_{\odot}})\), while effectively random for low- \((\mathrm{M_{\ast} \lesssim 10^9\; M_{\odot}})\) and high-mass \((\mathrm{M_{\ast} \gtrsim 10^{10.5}\; M_{\odot}})\) galaxies due to resolution effects and mergers, respectively. Black hole jets are well aligned with spin, and therefore also with galaxies, on Gyr time scales and 10 kpc to 10 Mpc physical scales. This further indicates that AGN jet observations may probe BH spin.Jet directions are slightly offset from the stellar angular momentum vector, while in projection, jets tend to be closely aligned with the semi-minor axis, which indicates that projection effects may likely be at play in AGN jet direction observations. These conclusions are insensitive to resolution and volume, although increasing the resolution significantly improves statistics. Observations of AGN jets systematically probe more massive galaxies due to selection effects and biases, which makes a fair comparison to simulations difficult. Nevertheless, simulations complement the observational picture, namely by providing predictions for lower-mass galaxies hosting AGN. The research presented in this thesis offers a first view into black hole jet alignments simulated with the new hybrid model and provides a useful qualitative view, although more accurate comparisons are needed in the future to confirm the results quantitatively.
Title: Investigating the spectral properties and tracing the atomic hydrogen in the major merger Mrk 273
Supervisors: Prof. Dr. Raffaella Morganti and Prof. Dr. Tom Oosterloo
Institution: University of Groningen
Abstract: Galactic mergers are an important step in galaxy evolution as they are thought to trigger the feeding mechanism of supermassive black holes by gas infall, eventually leading to an Active Galactic Nucleus (AGN). Ultra Luminous InfraRed Galaxies (ULIRGs) allow us to study this phenomenon because of their large dust quantities and association with late-stage major mergers and AGNs. The ULIRG Mrk 273 exhibits two large-scale (\(\sim 100\,\text{kpc}\)) radio jets. We investigate the spectral properties and HI distribution to determine their origin. We use Very Large Array (VLA) 1435 MHz continuum images in combination with LOFAR and archival VLA-C data to examine spectral properties. The Southern arc presents a perpendicular gradient steepening at higher frequencies and no steepening from the Northern arc. We reach a \(3 \times \sigma\) HI emission sensitivity of \(2.61 \cdot 10^{19} \,\text{cm}^{-2}\). No HI emission is detected on the arcs. We find two nuclear HI absorption components which are attributed to HI gas rotating around the nucleus. Based on an HI absorption column density of \(\sim 10^{22} \,\text{cm}^{-2}\) and no HI emission along the large-scale radio jets, we propose that a nuclear radio AGN is at the origin of large-scale jets. Our findings add to the pool of evidence supporting the phenomenon of merger events activating AGNs before coalescence and by extension at any point of the merging process, giving insights into the role of mergers in galactic evolution.