MeerKAT view of serendipitously detected giant radio galaxies (GRGs) from the MGCLS

Abstract

ABSTRACT Giant radio galaxies (GRGs; projected sizes $\gt \!0.7$ Mpc) remain key laboratories for understanding the long-term evolution of radio jets and their impact on large-scale environments. Recent wide-field surveys with Low Frequency Array (LoFAR), Australian Square Kilometre Array Pathfinder (ASKAP), and MeerKAT have significantly expanded the known GRG population. We present a uniform MeerKAT L-band analysis of six GRGs with projected sizes spanning $0.85\pm 0.02$ to $1.88\pm .0.02$ Mpc. Using in-band spectral-index mapping together with spatially resolved spectral-age modelling (JP/KP/Tribble), we derive integrated characteristic ages of $\sim 63$–254 Myr (mean $159\pm 26$ Myr), firmly placing these systems in a dynamically mature regime. The canonical pattern of flat-spectrum cores and progressively steeper lobe emission is recovered, with a sample-mean integrated spectral index of $\langle \alpha _{908}^{1656}\rangle =-0.86\pm 0.03$. The sample spans FR I, FR II, and bent morphologies, with several sources exhibiting coherent lobe asymmetries indicative of environmental modulation. In MKT J002659.83–121831.3 we identify two distinct electron populations, providing direct evidence for temporally separated injection episodes and demonstrating the power of broad-band spectral modelling to constrain active galactic nucleus duty cycles on $\gtrsim 10^8$ yr time-scales. The host galaxies are massive ($\gtrsim 10^{11}\, \mathrm{ M}_\odot$) and exhibit properties consistent with low-Eddington, radio-mode accretion. These results suggest that GRGs are long-lived, intermittently rejuvenated systems evolving close to pressure balance, offering important constraints on the cumulative mechanical feedback of radio jets.