Abstract :
Giant Radio Galaxies (GRGs) are home to active supermassive black holes that produce powerful bipolar radio jets, creating structures that extend over megaparsec scales. These are the largest structures in the Universe, growing up to ~7 Mpc and even surpassing the size of massive galaxy clusters. Though discovered 50 years ago, significant progress in understanding GRGs has been made only in the past eight years, largely due to the efforts of the SAGAN project ('Search & Analysis of GRGs with Associated Nuclei').
Research continues to explore whether the immense size of GRGs is driven by their efficient AGN or the sparser environments in which they reside. The
SAGAN project, initiated in 2016, has produced eight research papers, including a review, discovering the largest samples of GRGs and refining our understanding of their key properties. The project has rejuvenated global interest in these giant radio sources.
This seminar will review how our understanding of GRGs has evolved with deep radio surveys like LoTSS, which have uncovered the largest and faintest GRGs. We will discuss optical-infrared data from SDSS and WISE, revealing AGN accretion properties, and millimetre-wave data from IRAM, offering insights into AGN fuelling. We will also showcase GMRT radio images revealing previously unseen low-surface-brightness structures in GRGs, enabling more precise age and magnetic field estimates. Lastly, we will demonstrate how GRGs can be used as cosmic probes of large-scale environments and magnetic fields, with key implications for understanding magnetogenesis.
