Faint quasars at very low frequencies

In this thesis, we use low-frequency and high-frequency radio observations to address the following questions regarding quasars: is the radio loud/quiet quasar dichotomy real?; can deep low-frequency radio observations be used to effectively select high-z quasars?; how does the faint radio-selected quasar population evolve with redshift?; is the environment of quasars related to the origin of their radio-emission. For this purpose, we use low-frequency and high-frequency radio imaging, spectroscopic quasar catalogs, and ancillary optical and infrared data. The second chapter of the thesis uses existing radio and spectroscopic catalogs of quasars to study the clustering properties of RQQs and RLQs. The third chapter uses a directional-dependent calibration algorithm known as facet-calibration to obtain a deep LOFAR 150 MHz mosaic of the NOAO Deep Wide-Field Survey Bootes field. The remaining chapters combine the catalog obtained from the deep LOFAR mosaic presented with ancillary optical/infrared data to study the selection of high-z quasars using LOFAR observations, and to investigate the evolution of radio-selected quasars with redshift.