Widening the field-of-view of Very Long Baseline Interferometric surveys through advanced calibration techniques

Abstract

Very long baseline interferometry (VLBI) is a vital tool in astronomy that unlocks extremely high resolutions with high sensitivity. The fields of view (FoVs) of VLBI observations historically were limited by bandwidth and time smearing, as well as signal attenuation experienced by the array elements due to their primary beams. Technological upgrades and improved correlation and calibration techniques have largely eliminated smearing, leaving the primary beams as the last major FoV restriction. In this thesis, we derive primary beam models for a large subset of antennas in the European VLBI Network (EVN) and enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) using an observation scheme similar to out-of-focus holography (OOF). These models are also applied to a wide-field observation of the Hubble Deep Field-North (HDFN) to test their efficacy in removing beam-related attenuation. Obtaining accurate primary beam models of the antennas in VLBI networks would allow for wide-field observations’ development to accelerate and unlock many new facets of science, including active galactic nuclei (AGN) surveys, AGN feedback studies, gravitational lens surveys, and interstellar medium density studies, to only mention a few. In this project, we also face the additional challenge of modelling heterogeneous arrays, meaning that different primary beams are present in the data.