Is J 133658.3-295105 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 J 133658.3–295105. This source has been suggested to be the core of an FR II radio source with two detected lobes. J 133658.3–295105 and its lobes are aligned with the optical nucleus of M83 and with three other radio sources at the M83 bulge outer region. These radio sources are neither supernova remnants nor Hii regions. This curious configuration prompted us to try to determine the distance to J 133658.3–295105. We detected Hα emission redshifted by ≈ 130 km s-ˡ with respect to an M83 Hii region 2"5 east-southeast of the radio source. We do not detect other redshifted emission lines of an optical counterpart down to mi = 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.