The thesis deals with the study of giant radio galaxies (GRGs), which are radio galaxies of megaparsec sizes. Their enormous size and rarity have been investigated in this thesis. The study... Show moreThe thesis deals with the study of giant radio galaxies (GRGs), which are radio galaxies of megaparsec sizes. Their enormous size and rarity have been investigated in this thesis. The study included searching and consequent finding of the largest samples of GRGs and thereby enabling to study of their properties in detail. Also, the properties were compared to smaller sized radio galaxies to investigate possible differences which could be the factor for their giant sizes. Show less
Paul, S.; Gupta, P.; Salunkhe, S.; Bhagat, S.; Sonkamble, S.; Hiray, M.; ... ; Raychaudhury, S. 2021
We present a deep XMM-Newton observation of the extremely massive, rapidly rotating, relativistic-jet-launching spiral galaxy 2MASX J23453268-0449256. Diffuse X-ray emission from the hot gaseous... Show moreWe present a deep XMM-Newton observation of the extremely massive, rapidly rotating, relativistic-jet-launching spiral galaxy 2MASX J23453268-0449256. Diffuse X-ray emission from the hot gaseous halo around the galaxy is robustly detected out to a radius of 160 kpc, corresponding roughly to 35 per cent of the virial radius (approximate to 450 kpc). We fit the X-ray emission with the standard isothermal beta model, and it is found that the enclosed gas mass within 160 kpc is 1.15(-0.24)(+0.22)x10(11)M(circle dot) . Extrapolating the gas mass profile out to the virial radius, the estimated gas mass is 8.25(-1.77)(+1.62)x10(11)M(circle dot), which makes up roughly 65 per cent of the total baryon mass content of the galaxy. When the stellar mass is considered and accounting for the statistical and systematic uncertainties, the baryon mass fraction within the virial radius is 0.121(-0.043)(+0.043),in agreement with the universal baryon fraction. The baryon mass fraction is consistent with all baryons falling within r(200), or with only half of the baryons falling within r(200). Similar to the massive spiral galaxies NGC 1961 and NGC 6753, we find a low value for the metal abundance of approximate to 0.1 Z(circle dot), which appears uniform with radius. We also detect diffuse X-ray emission associated with the northern and southern lobes, possibly attributed to inverse Compton scattering of cosmic microwave background photons. The estimated energy densities of the electrons and magnetic field in these radio lobes suggest that they are electron-dominated by a factor of 10-200, depending on the choice of the lower cut-off energy of the electron spectrum. Show less
Dabhade, P.; Mahato, M.; Bagchi, J.; Saikia, D.J.; Combes, F.; Sankhyayan, S.; ... ; Guiderdoni, B. 2020
Giant radio galaxies (GRGs) are one of the largest astrophysical sources in the Universe with an overall projected linear size of ∼0.7 Mpc or more. The last six decades of radio astronomy research... Show moreGiant radio galaxies (GRGs) are one of the largest astrophysical sources in the Universe with an overall projected linear size of ∼0.7 Mpc or more. The last six decades of radio astronomy research has led to the detection of thousands of radio galaxies. However, only ∼300 of them can be classified as GRGs. The reasons behind their large size and rarity are unknown. We carried out a systematic search for these radio giants and found a large sample of GRGs. In this paper, we report the discovery of 25 GRGs from the National Radio Astronomy Observatory Very Large Array Sky Survey, in the red-shift range z ∼ 0.07 to 0.67. Their physical sizes range from ∼0.8 Mpc to ∼4 Mpc. Eight of these GRGs have sizes ≥2 Mpc, which is a rarity. Here, for the first time, we investigate the mid-infrared (IR) properties of the optical hosts of the GRGs and classify them securely into various active galactic nuclei types using the WISE mid-IR colours. Using radio and IR data, four of the hosts of the GRGs were observed to be radio-loud quasars that extend up to 2 Mpc in radio size. These GRGs missed detection in earlier searches possibly because of their highly diffuse nature, low surface brightness and lack of optical data. The new GRGs are a significant addition to the existing sample. They will contribute to a better understanding of the physical properties of radio giants. Show less
