Research Projects

Giant radio galaxies (GRGs) are an extreme class of active galaxies with linear sizes in the range ∼ of 0.7 to 5 Mpc, placing them among the largest single astrophysical objects known to us. The first GRG, 3C236, was discovered about50 years ago by Willis et al. (1974). Out of many thousands of radio galaxies discovered in the past 50 years of radioastronomy, only about 700 have been identified as GRGs. Moreover, until now, only a small fraction of these GRGs have been studied in sufficient detail in multiple wavebands for achieving a good understanding of their unusual nature. These radio sources are supposed to born in the active nuclei (AGN) located at the galactic centres. It is believed that so called ‘central engine’ is an accreting super-massive black hole (SMBH) of mass 108−1010Msun , which is responsible for the ejection of the collimated, bipolar relativistic jets orthogonal to an accretion disk (Lynden-Bell,1969; Begelman et al., 1979). Understanding their formation (birth), evolution, the duty cycle of radio activity, and especially the influence of the surrounding intergalactic medium (IGM), which confines the lobes far away from the host galaxy and provides a ‘working-surface’ for the jets to act, are among the most important problems in this field. It was shown by Safouris et al. (2009) that GRGs can serve as outstanding probes of the IGM via the relationship between the morphology of the radio galaxy and the properties of the surrounding material which is part of the large-scale cosmic-web. Thus, GRGs may also play an important role in the high energy processes related to large-scale structure formation in the Universe. One of the common explanations for the gigantic size of GRGs is attributed to the less dense IGM around them, which allows them to expand and grow unhindered (Mack et al., 1998; Lara et al., 2004;Jamrozy et al., 2008; Subrahmanyan et al., 2008; Malarecki et al., 2015). In other words, this implies that GRGs are preferentially born in a sparse galactic environment. BCGs typically do host radio lobes powered by AGN outbursts, although on much smaller scales than seen in GRGs. In cool-core clusters, these radio lobes are known to play a very important role in the evolution of the BCG itself, by pumping energy into the surrounding intra-cluster medium (ICM) and preventing cooling and star-formation that would lead to a dramatic growth of the AGN’s host galaxy(e.g., Br ̈uggen & Kaiser, 2002). Astronomers Pratik dhabahde, Gaikwad, Madhuri, Bagchi, Joydeep and their colleagues, have discovered reason-able number of GRGs using the NRAO VLS sky survey (NVSS-1.4 GHZ) (Dabhade et al., 2017, 2020b). Here, I am showing a peculiar giant radio galaxy as a prototype in this class (see. Figure.1). In this figure, radio images and spectral indices of GRGJ223301+131501 obtained with GMRT are shown.