The head-tail radio galaxy and revived fossil plasma in Abell 1775

In galaxy clusters, radio band observations reveal synchrotron emission originating from both individual radio galaxies and diffuse radio sources. Head-tail radio galaxies exhibit distinctive features where the head corresponds to an elliptical galaxy and two jets/tails sweep back from the head forming an extended structure behind the radio galaxy, that is moving through ICM. This morphology arises from the interplay between the diffuse radio-emitting plasma being decelerated by ICM. In contrast, revived fossil plasma trace AGN radio plasma with a very steep spectrum that has somehow been re-energized through processes in the ICM, unrelated to the radio galaxy itself. In this thesis, our focus is on studying the central region of Abell 1775, a galaxy cluster in an unclear dynamical state, at redshift z = 0.07203. This region hosts two giant radio-loud elliptical galaxies, the southeastern one B1339+266B hosts a head-tail radiogalaxy that “breaks” at the position of a cold front detected in the X-rays, revived fossil plasma, and central diffuse emission. The aims of this study are to investigate and constrain the spectral properties and trends along the head-tail, as well as the study of the revived fossil plasma, to better understand the process of formation of the non-thermal phenomena in A1775. In this respect, we made use of LOFAR 144 MHz, new deep uGMRT 400 MHz, and 650 MHz radio data. We observe an overall steepening along the tail of the head-tail radio galaxy. The newly obtained radio color-color diagrams for this radio source compared with standard aging models, imply an ongoing particle re-acceleration in the outer regions of the tail. We speculate contamination from filaments emission in the inner tail. An unexpected increase of the brightness at the head of the tail was observed indicating a complex bending of the jets near the head. Based on the low-frequency spectral index analysis we conclude that F1 and F2 filaments have an ultra-steep spectrum.