A gamma-ray-emitting head-tail radio galaxy swimming through the hot medium of the merging cluster A3627

Abstract

Head–tail radio sources are jetted active galactic nuclei (AGN) moving through the dense intracluster medium of galaxy clusters. They are extremely rare in the γ-ray sky, likely because they are usually observed at large viewing angles. Therefore, every new γ-ray detection of head–tail radio galaxies allows us to probe the origin of the highenergy emission in this unique class of AGN. Here we report, for the first time, the association of ESO 0137−G007 (z = 0.016), a head–tail radio galaxy located at the outskirts of the merging cluster A3627, with the γ-ray source FL16Y J1615.5−6034. The motion of the galaxy through the dense cluster environment and subsequent ram pressure and/or intracluster medium turbulence have led to the formation of a >500 kpc long jet exhibiting a twisted, wiggly radio morphology. Its optical spectrum, obtained with the 4.1 m SOAR telescope, is devoid of emission lines, indicating that the underlying accretion activity is radiatively inefficient. From the measured line-of-sight stellar velocity dispersion, we estimate the mass of the central supermassive black hole to be (3.36 ± 1.32) × 10^9 M⊙. We briefly discuss several radiative models to explain the observed broadband spectral energy distribution of ESO 0137 −G007. We conclude that deeper multiwavelength observations of this unique γ-ray-emitting head–tail radio galaxy will enable us to better understand the interaction of the jet with the hot cluster environment, thus setting the stage for the research of this class of AGN with the upcoming Square Kilometre Array.