High-resolution imaging of the radio continuum and neutral gas in the inner kiloparsec of the radio galaxy 3C 293

Abstract

Using a combination of observations involving the Very Large Array (VLA), MERLIN and global Very Long Baseline Interferometry (VLBI) networks we have made a detailed study of the radio continuum and the neutral hydrogen (H i) kinematics and distribution within the central kiloparsec of the radio galaxy 3C 293. These observations trace the complex jet structure and identify the position of the steeply inverted radio core at 1.3 GHz. Strong H i absorption is detected against the majority of the inner kiloparsec of 3C 293. This absorption is separated into two dynamically different and spatially resolved systems. Against the eastern part of the inner radio jet, narrow H i absorption is detected and shown to have higher optical depths in areas cospatial with a central dust lane. Additionally, this narrow line is shown to follow a velocity gradient of ∼50 km s−1 arcsec−1, consistent with the velocity gradient observed in optical spectroscopy of ionized gas. We conclude that the narrow H i absorption, dust and ionized gas are physically associated and situated several kiloparsecs from the centre of the host galaxy. Against the western jet emission and core component, broad and complex H i absorption is detected. This broad and complex absorption structure is discussed in terms of two possible interpretations for the gas kinematics observed. We explore the possibility that these broad, double absorption spectra are the result of two gas layers at different velocities and distances along these lines of sight. A second plausible explanation for this absorbing structure is that the H i is situated in rotation about the core of this radio galaxy with some velocity dispersion resulting from infall and outflow of gas from the core region. If the latter explanation were correct, then the mass enclosed by the rotating disc would be at least 1.7 × 109 solar masses within a radius of 400 pc.