Shedding light on giant radio sources
Giant radio sources (GRSs) are the active galactic nuclei (AGNs) that propel relativistic jets to mega-parsec scales, and project a linear size greater than 0.7 Mpc. They can be associated with both galaxies (GRGs) and quasars (GRQs). They are very much important for understanding the growth and evolution of radio galaxies and quasars to such gigantic scales, and to probe their environment. We have created a large database of GRGs -the GRG catalogue, and GRQs- the GRQ catalogue from the literature, and studied their multi-wavelength properties to understand their nature. We have also compiled small radio galaxy (SRG) and small radio quasar (SRQ) samples to carry out a systematic comparative study of the giant radio sources with the smaller ones using mid-infrared, optical and radio data. Our results show that the giant and the smaller ones statistically have similar radio spectral index and black hole mass distributions. However, the small sources have a higher radio core power, core dominance factor, total radio power, jet kinetic power, and Eddington ratio compared to the giants. The high core dominance factor of SRQs is an indicator of them lying closer to the line of sight than GRQs. Using the mid-infrared data, we have classified GRGs in terms of their accretion mode: either a high-power radiatively efficient high-excitation state, or a radiatively inefficient low-excitation state. We find that GRGs in high-excitation state statistically have larger sizes, stronger radio power, jet kinetic power, and higher Eddington ratio than those in low-excitation state. We also find a correlation between the accretion disc luminosity and jet power of giants, which provides evidence for disc-jet coupling. Lastly, we find the distributions of Eddington ratios of GRGs and GRQs to be bi-modal, similar to that found in SRGs and SRQs, which indicates that size is not strongly dependent on the accretion state. We discuss their formation and growth scenarios, highlighting the key physical factors that cause them to reach their gigantic size.