A new look at old devils. II: New insights on classical radio galaxies from MeerKAT and uGMRT

Abstract

This paper presents a detailed morphological and spectral analysis of a sample of ten radio galaxies observed with the MeerKAT in L-band (856 – 1712 MHz) and the upgraded Giant Metrewave Radio Telescope in Band-4 (550 – 850 MHz). Our main goals are to revisit the current classification scheme for classical radio galaxies and study the properties of new radio features in jets, lobes and hot spots, which are becoming increasingly numerous due to the sensitivity and imaging capabilities of current radio interferometers, and suggest previous unexplored interaction mechanisms between the radio plasma and the external medium. The sample from the 4C catalogue includes FR I, FR II, wide-angle and narrow-angle tailed sources as well as FR 0 radio galaxies from FR0CAT, with redshifts ranging from 0.04 – 0.20. The high angular resolution, ~4″ – 10″ total intensity images are presented, revealing complex structures in the jets, lobes and hotspots of these sources. The integrated spectra of the sources, constructed using flux density measurements from our observations and archival data, reveal spectral breaks and slopes indicative of radiative ageing, with ages spanning ~40 – 242 Myr. While the sample broadly confirms the classical FR classification as a useful first-order scheme, the substructures within the radio emission of sources highlight the need for models that incorporate environmental complexity and episodic jet activity to fully describe radio-galaxy evolution.