Discovery of a spiral-host episodic radio galaxy

Abstract

Abstract We report the discovery of a unique radio galaxy at z= 0.137, which could possibly be the second spiral-host large radio galaxy and also the second triple—double episodic radio galaxy. The host galaxy shows signs of recent star formation in the ultraviolet but is optically red and is the brightest galaxy of a possible cluster. The outer relic radio lobes of this galaxy, separated by ∼1 Mpc, show evidence of spectral flattening and a high fraction of linear polarization. We interpret that these relic lobes have experienced re-acceleration of particles and compression of the magnetic field due to shocks in the cluster outskirts. From the morphology of the relics and galaxy distribution, we argue that re-acceleration is unlikely to be due to a cluster—cluster merger and speculate about the possibility of accretion shocks. The source was identified from Sloan Digital Sky Survey, Galaxy Evolution Explorer, NRAO VLA Sky Survey and Faint Images of the Radio Sky at Twenty-Centimetres survey data, but we also present follow-up optical observations with the Lulin telescope and 325-MHz low-frequency radio observations with the Giant Metrewave Radio Telescope. We briefly discuss the scientific potential of this example in understanding the evolution of galaxies and clusters by accretion, mergers, star formation and active galactic nucleus feedback.