Is J133658.3-295105 A radio source at z ≥ 1.0 or at the distance of M 83?

Abstract

We present Gemini optical imaging and spectroscopy of the radio source J133658.3-295105. Thisd source has been suggested to be the core of an FR II radio source with two detected lobes. J133658.3-295105 and its lobes are aligned with the optical nucleus of M 83 and with three other radio sources at the M 83 bulge outer region. These radio sources are neither supernova remnants nor H II regions. This curious configuration prompted us to try to determine the distance to J133658.3-295105. We detected Hα emission redshifted by 130 km s-1 with respect to an M 83 H II region 25 east-southeast of the radio source. We do not detect other redshifted emission lines of an optical counterpart down to m i = 22.2 0.8. Two different scenarios are proposed: the radio source is at z ≥ 2.5, a much larger distance than the previously proposed lower limit z ≥ 1.0, or the object was ejected by a gravitational recoil event from the M 83 nucleus. This nucleus is undergoing a strong dynamical evolution, judging from previous three-dimensional spectroscopy.