SO Colloquium – Giant radio sources and their episodic nuclear activity

Radio galaxies and quasars are among the most luminous and largest single structures in our Universe ranging in size from parsecs to several Mpc. The giant radio sources (GRSs), defined to be those with a projected linear size >700 kpc, pose a number of interesting astrophysical questions and are also valuable probes of the intergalactic environment. We examine critically different scenarios for their formation and evolution including insights from our discovery of such large sources associated with narrow line Seyfert 1 galaxies, which are believed to harbour lower mass super-massive black holes.

Giant radio sources are believed to be inclined at large angles to the line of sight, unlike blazars whose jets are almost pointed at us. The bulk of the active galactic nuclei (AGN) detected at gamma rays are associated with blazars. However, from a careful multi-wavelength study, we have been able to identify a significant population of misaligned gamma-ray emitting AGN associated with radio galaxies, tripling the previously known numbers. This includes a small population of GRSs, most of which were previously unknown. We discuss the implications of these in our understanding of GRSs.

One of the most striking examples of episodic nuclear jet activity in AGN are the double-double radio galaxies with two or more pairs of distinct lobes on opposite sides of the nucleus. Episodic nuclear activity has been suggested to be one of the models for the formation of GRSs. We give a brief overview of episodic nuclear activity, and critically examine this possibility for GRSs. We highlight the important role that LOFAR has played in these studies, and an even more significant role that SKA will play in the future.

Fecha y lugar: 09/04/2026 – 12:30 | Salón de Actos
Dhruba Saikia
Inter-University Centre for Astronomy and Astrophysics (IUCAA)