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

Giant radio galaxies (GRGs; projected sizes >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 ± 0.02 to 1.88 ± .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 ∼63-254 Myr (mean 159 ± 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 α ₉₀₈¹⁶⁵⁶ =-0.86± 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 broadband spectral modelling to constrain AGN duty cycles on ≳ 108 yr timescales. The host galaxies are massive (≳ 1011 M⊙) 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.