Letter to the Editor

Serendipitous discovery of a spiral host in a 2 Mpc double-double lobed radio galaxy

¹ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
² Doctoral School of Exact and Natural Sciences, Jagiellonian University, Kraków, Poland
³ Queen Jadwiga Astronomical Observatory in Rzepiennik Biskupi, 33-163 Rzepiennik, Strzyżewski, Poland

^⋆ Corresponding authors: sagar.sethi@doctoral.uj.edu.pl, agn.kuzmicz@uj.edu.pl

Received: 1 April 2025
Accepted: 5 May 2025

Abstract

We present the serendipitous discovery of a double-double radio galaxy (DDRG) with a projected linear size exceeding 2 Mpc, hosted by a spiral galaxy. This unique combination of a giant radio structure and a spiral host challenges the prevailing view that such extreme radio sources reside only in elliptical galaxies. Using high-resolution optical imaging from the DESI Legacy Imaging Survey (DR10), we confirm a spiral-arm feature and a disc component in the surface brightness profile fitting for the host galaxy (LEDA 896325) that has a black hole of mass 2.4 × 10⁸ M_⊙. Radio observations from RACS and GLEAM reveal two distinct pairs of radio lobes. Using the multi-frequency analysis of radio data, we obtained the spectral index distribution and estimate the spectral ages of the outer and inner radio lobes to be approximately 120 and 35 Myr, respectively. Our results confirm recurrent jet activity in this disc galaxy and establish it as the largest known radio galaxy in a spiral host, and its double-double structure makes it the largest of only three such spiral-host DDRGs, demonstrating that disc galaxies can indeed launch extremely large-scale radio jets.