When the launching of powerful supermassive black hole jets persists over megayears, these flows become the largest galaxy-made structures in the Universe, attaining multi-megaparsec extents. By pumping thermal, magnetic, and cosmic ray energy far beyond galactic borders, megajets affect the distribution of matter and magnetism in the Cosmic Web. Over the last years, thanks to sensitivity gains of large-scale radio surveys, such as LOFAR's, it has become clear that megajets — generally thought to be rare and cosmologically insignificant only years ago — are not only common, but possibly the dominant source of black hole feedback to the Cosmic Web. A resurgence in interest in megajets coincides with the realisation that leading cosmological simulations feature insufficient large-scale baryonic feedback, affecting cosmologists' ability to infer cosmological parameters from the newest surveys  such as DESI's, Euclid's, and the LSST. 

To improve simulations and realise precision late-time cosmology with these flagship surveys, it is a priority to understand the origin and cosmological impact of megajets. This talk presents recent results on gaseous disks in megajet host ellipticals and on the megajet energy injection rate per unit of comoving volume, and explores whether megajets can have caused magnetogenesis in voids. These investigations are powered by cutting-edge Keck II IFS and recent LOFAR data.