Supermightee: spectral ages of remnant radio galaxy candidates in the XMM–LSS field

Abstract

Remnant radio galaxies, whose lobes are no longer replenished by jets from the active galactic nucleus (AGN), offer key constraints on AGN duty cycles and the time-scales of radio jets. We present a spectral-ageing study of 14 candidate remnant radio galaxies in the XMM(Formula presented) LSS field, combining new broad-band data from the MeerKAT MIGHTEE ((Formula presented) band) and uGMRT superMIGHTEE (band-3 and band-4) surveys with complementary observations from LOFAR, GMRT, and JVLA, covering 144 MHz(Formula presented) 1.5 GHz. Spectral modelling confirms 12 sources as genuine remnants, while two are reclassified as active, emphasizing the importance of sensitive, multifrequency coverage for robust remnant identification. Pixel-based spectral age maps yield results ((Formula presented) 3–43 Myr) broadly consistent with integrated estimates, revealing relatively short spectral ages ((Formula presented) 8–42 Myr). These ages likely reflect enhanced inverse-Compton losses at higher redshifts (0.35 (Formula presented) z (Formula presented) 2.85; median z = 1.25) and possible rapid lobe expansion in low-density environments. The ratios of remnant to total source ages (t(Formula presented) /t(Formula presented)) span 0.04–0.83, indicating that the sample traces a broad range of evolutionary stages. Our findings reveal a previously underrepresented population of faint, rapidly fading remnants, suggesting that the remnant phase may be shorter and more dynamic than previously thought. This study highlights the crucial role of MIGHTEE and superMIGHTEE surveys in reliably classifying genuine remnants and provides a framework for constraining AGN life cycles in preparation for forthcoming SKA surveys.