Jets in radio galaxies and quasars: an observational perspective

Abstract

This article gives a brief historical introduction and reviews our current understanding of jets in radio galaxies and quasars from an observational perspective, with an emphasis on observations at radio wavelengths. Recent results on the Fanaroff-Riley (FR) classification scheme, and the nature of radio structures and jets in the FR classes as well as in high-excitation and low-excitation radio galaxies are summarized. The collimation and propagation of jets from nuclear sub-pc to hundreds of kpc scales from both observational and theoretical work have been discussed. The jets exhibit evidence of interaction with a clumpy interstellar medium, especially in young radio sources, and could trigger both star formation as well as suppress star formation depending on the physical conditions. Observational evidence for such interactions and jet feedback which have profound implications in our understanding of galaxy evolution have been presented. Recurrent jet activity which has been seen over a wide range of projected linear size and time scales has been discussed. This review article concludes with a brief discussion of unresolved questions on jets which new telescopes should help address.

Barbell-shaped giant radio galaxy with ∼100 kpc kink in the jet

“…On the other hand, the lobes appear to be relics with no hotspots. In this case, if the jets are from a more recent cycle of activity, the velocity of the jets could be significantly higher, as seen in detailed models of jets (see review by Saikia 2022).…”

“…The properties of jets in radio-loud AGN (RLAGN), which include both RGs and RQs, and our current understanding have been reviewed recently (e.g. Blandford et al 2019;Hardcastle & Croston 2020;Saikia 2022). RLAGN with an overall projected linear size greater than 0.7 megaparsec (Mpc) are defined as giant radio sources (GRSs); those associated with galaxies and quasars are referred to as giant radio galaxies (GRGs) and giant radio quasars (GRQs), respectively.…”

Characteristics of remnant radio galaxies detected in the deep radio continuum observations from the SKA pathfinders

“…Radio galaxies, a subclass of active galactic nuclei (AGN), exhibit highly collimated bipolar jets supplying plasma to radio lobes at large distances of hundreds of kilo-parsecs (see Hardcastle & Croston, 2020;Saikia, 2022). The radio jets launched from the vicinity of an accreting super-massive black hole (SMBH) offer a direct probe to the status of AGN activity.…”