We explored how to morphologically classify well-resolved jetted radio-loud active galactic nuclei (RLAGN) in the LOw Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) using machine learning.We... Show moreWe explored how to morphologically classify well-resolved jetted radio-loud active galactic nuclei (RLAGN) in the LOw Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) using machine learning.We investigated what morphology in total radio intensity maps can tell us about observed radio sources without complementary wavelength information and with limited visual inspection. We used a self-organising map (SOM) to model common radio morphologies and to reveal the rarest morphologies in LoTSS.Furthermore, we turned the radio source-component association problem into an object detection problem and trained an adapted Fast region convolutional neural network to mimic the grouping of source components into unique sources as performed by astronomers for LoTSS data.We also reduced the visual inspection required to find RLAGN remnant candidates based on their morphology, by using SOM-based features as input for a random forest classifier.Finally, we created a machine learning pipeline to identify giant radio galaxy (GRG) candidates and created a sample that contains more than ten thousand GRG. We then quantified the intrinsic GRG proper length distribution, the comoving GRG number density, and a current-day GRG lobe volume-filling fraction in clusters and filaments of the Cosmic Web. Show less
An Active Galactic Nucleus (AGN) is a highly luminous region at the center of a galaxy, powered by the accretion into a supermassive black hole and emitting energy from radio waves to gamma rays,... Show moreAn Active Galactic Nucleus (AGN) is a highly luminous region at the center of a galaxy, powered by the accretion into a supermassive black hole and emitting energy from radio waves to gamma rays, often outshining the host galaxy. In the context of the AGN unification paradigm, the concept of the dusty “torus” plays a crucial role to discern between Type-1 and Type-2 AGNs depending on whether it obscures the AGN from the observer’s line of sight. NGC 1068, a well-studied AGN across the electromagnetic spectrum, is a nearby barred galaxy (d=14.4 Mpc) considered the prototypical Type-2. Using MATISSE at the VLTI, we have obtained direct evidence of the dusty torus enshrouding the AGN in NGC 1068. The multi-band capabilities of the instrument in the infrared wavelengths and the high spatial resolution that the interferometric technique can achieve have enabled us to study in detail the characteristics of the obscuring dust and its spatial distribution. We further analyse ALMA observations of the molecular gas with a comparable angular resolution. The revealed kinematics suggest an ongoing merger event, potentially contributing to the observed asymmetries in the torus and the water-maser disk, offering new insights into the dynamic processes in AGNs. Show less
The radio sky harbours both galactic and extragalactic sources of arcminute- to degree-scale emission of various physical origins. To discover extragalactic diffuse emission in the Cosmic Web... Show moreThe radio sky harbours both galactic and extragalactic sources of arcminute- to degree-scale emission of various physical origins. To discover extragalactic diffuse emission in the Cosmic Web beyond galaxy clusters, one must image low–surface brightness structures amidst a sea of brighter compact fore- and background sources. Angularly separating the faint from the bright radio sky requires high-quality ionospheric calibration. This thesis introduces new advances in and investigations into ionospheric calibration, the degree-scale Milky Way foreground, and two sources of megaparsec-scale emission in cosmic filaments: giant galactic outflows and cosmological structure formation shocks. Giant galactic outflows (or ‘giant radio galaxies’) are generated by the jets of active supermassive black holes, and transport relativistic leptons, entrained atomic nuclei, heat, and magnetic fields from the centres of galaxies to their outskirts and beyond. These outflows embody the most energetic pathway by which galaxies respond to the Cosmic Web around them. Structure formation shocks around filaments are a generic, but still elusive, prediction of cosmological simulations and trace the gravitational flow of matter from proto-voids to filaments. Both phenomena inform on the strength, topology, and origin of magnetic fields in the Cosmic Web. Show less
