Radio astronomy with LOFAR-VLBI on new generation HPC systems: the case of Abell 2255

This Thesis work focuses on the exploitation of new HPC systems for modern and future radio interferometers, addressing both computational and scientific challenges. Computationally, we describe the development of RICK, a code which addresses the interferometric imaging exploiting advanced parallel and accelerated solutions. RICK uses a distributed approach to the problem, dividing the input dataset among multiple CPUs/GPUs in multiple nodes. The main feature of RICK is the possibility to run entirely on GPUs, deploying several optimized libraries which are novel to radio astronomy. RICK was extensively tested on real ILT data, with huge improvements when executed fully on GPUs. While not yet ready for scientifically valid maps, we proved the large potential of this approach for interferometric imaging. Scientifically, the main activity of this Thesis is the usage of ILT data to study the radio galaxies and the associated filamentary emission in the galaxy cluster Abell 2255. Combining multiple observations, we produced sub-arcsecond resolution images of the brightest cluster member radio galaxies. For one target, namely the Original Tailed Radio Galaxy, we discovered the presence of several filamentary emission surrounding its tail, detectable only with such deep, low-frequency and high-resolution observations. To constrain their origin, we have imaged the whole cluster’s field of view, calibrating the ILT data in the so-called wide-field mode. The resulting map revealed the existence of additional filaments not directly related to any radio galaxy. We determined the spectral properties of the filaments and, consequently, an estimate on their radiative ages and equipartition magnetic fields. Polarization was also measured for parts of one filament. The spectral properties, together with the shape, suggest that these filaments could identify regions characterized by low-beta plasma, that is the presence of large magnetic fields, possibly enhanced by magnetic line stretching, or depletion of thermal plasma.