Speaker
Description
One of the most common explanations for the existence of megaparsec-scaled radio galaxies (also called giant radio galaxies or GRGs) is that they are older sources. However, this hypothesis has not been thoroughly tested on a statistically large sample, —attributable primarily to the demand for multifrequency data that spans a broad spectrum from low to high frequencies, matched in sensitivity and spatial resolution. The advent of LoFAR in recent years has made such analyses feasible, offering superior sensitivity and resolution at low frequencies, which is crucial for constraining injection index in spectral ageing analysis. GRGs that surpass 2 Mpc (largest) in size are uncommon, constituting less than ~10% of the GRG population. Consequently, we have selected a sample of the largest and brightest GRGs, all exceeding 2 Mpc, totalling eight sources (7 GRGs, 1 GRQ). These were meticulously observed using our dedicated observations with LoFAR (21hr), uGMRT (47hr), and JVLA (7hr), covering a frequency range from 150 MHz to 10 GHz. We have carried out detailed spectral and dynamical age modelling over a wide range of frequencies using packages like Synage, BRATS, Dynage and RAiSE HD and also compare them. We will for the first time present detailed spectral ageing analysis of the largest giants using our deep mutli-frequency data spanning 150 MHz to 10 GHz, which allows us to reliably determine the break frequencies. Additionally, we also examine the comparison between dynamical and radiative ages of these sources. Using our multi-frequency high resolution deep radio maps we have also explored core properties and hotspot features. Interestingly, all GRGs in our sample exhibit a high axial ratio, and most have conical hotspots on both sides. In this oral presentation, I will present our meticulous work, encompassing the acquisition of multifrequency data, its subsequent analysis, and the comprehensive process of integrating these insights into detailed modeling to decipher the nature of the largest giants.
