MIGHTEE: Discovery of a triple-double radio galaxy

TL;DR

This paper reports the discovery of a rare triple-double radio galaxy using MIGHTEE data, providing insights into its structure, environment, and recurrent nuclear activity through spectral analysis.

Contribution

It presents the first detailed spectral age analysis of a newly discovered TDRG, challenging previous assumptions about long inactive periods between activity cycles.

Findings

Discovered a new TDRG at z ≈ 0.94 with triple-double lobes.

Spectral analysis indicates a rapid duty cycle of 90%.

Spectral age fitting suggests a total age of ~16 Myr.

Abstract

Triple-double radio galaxies (TDRGs) are amongst the rarest subpopulations of radio galaxies (RGs). They are characterised by three pairs of radio lobes, where each pair of lobes represents an episode of nuclear activity. Such a feature makes them key objects that can be used to constrain the duty cycle of RGs. In this paper, we report the discovery of J022248\m060934, a new TDRG, hosted by a galaxy at a spectroscopic redshift of $z \approx$ 0.94. We have used the MIGHTEE-DR1 data set and MIGHTEE sub-band images as our main data. In total intensity, J022248\m060934 has a bright core and triple-double, edge-brightened-like peaks of radio emission. The polarimetry of the source reveals an inhomogeneous density of the hosting environment which is consistent with the more pronounced bending in its eastern lobes. The spectral index and curvature maps suggest an inverted core and an ultra-steepening of the spectrum towards the outer lobes which reinforce a recurrent nuclear activity. We perform individual spectral age fitting of the components of the source using the JP model and we found a lower limit total age of $\sim$16 Myr. We also derive a short inactive period between the active phases and a rapid duty cycle of 90 per cent for the first cycle of activity. Our spectral ageing analysis suggests that the triple-double structure in TDRGs is not the product of long quiescent periods, as deduced by previous works based on kinematic ages.