Multifrequency images of 3 giant radio galaxies

In this study, we perform multifrequency radio observations of the selected sources with Karl G. Jansky Very Large Array and the upgraded Giant Metrewave Radio Telescope. Analysis of the radio-lobe morphology and the structure of the spectral index maps provides preliminary information about the sources' environment and activity. Outer doubles with asymmetric backflows and minor misalignments were observed in J1021+1216, J1528+0544, and J2345-0449.

In J2345-0449, there appear low surface brightness wings close to the core. In all three sources, the shorter lobe is the brighter one, suggesting the existence of large scale inhomogeneties in the ambient medium. A trace of emission with low values of spectral index appears in the J1528+0544 outer double maps, possibly marking the orientation of the jet in the initial phase of activity.

Asymmetries of the inner lobes in J1021+1216 and J2345-0449 can be explained by relativistic Doppler effect, while the J1528+0544 inner double structure requires a contamination of the radio cocoon. The shown examples of asymmetric backflows and wings in the outer doubles of the studied sources show the existence of inhomogeneities of the external medium around the host galaxies on the scale of the radio-lobe size, suggesting a complex evolution of the radio cocoons.

The initial jets seem to clear the ambient medium for the subsequent phases of activity. Spectral aging analysis and dynamical modeling, made in the second part of this study, are necessary to confirm the results.