The dynamics of the S0 galaxy IC 5063*

Low-dispersion spectrophotometry of the S0 galaxy IC 5063 suggests there is an intense hot source at its centre, photo-ionizing not only its immediate surroundings but also regions of the gaseous disc at large distances from the centre. Long slit spectroscopy with an IPCS reveals circular motion in the gaseous disc with an observed amplitude of 185 km s⁻¹ and a real amplitude of 226 km s⁻¹. The rotation curve of the disc remains flat out to the furthest observed point at 10 kpc, implying a mass of $$\sim0.9\times10^{11}M_\odot$$ and a mass-to-light ratio $$M/L_\text B=4.1$$ interior to this point; it also implies a significant amount of under-luminous mass beyond it. Interior to 1 kpc the stellar component appears to be rotating with an observed amplitude of 125 km s⁻¹, which implies a rotational velocity similar to that of the gaseous disc at the same radial distance. The morphology of the galaxy and spatial extension of the emission lines are consistent with the gaseous disc's being warped and optically thick to ionizing radiation from the central source. The 21 cm line of neutral hydrogen has been detected in emission from this galaxy with a systemic velocity and width almost precisely that observed for the ionized gas. Therefore the observed neutral gas appears to be following the same rotational motion as the ionized gas. The mass of neutral hydrogen is $$10^{10}M_\odot$$. Radio continuum observations at 21 cm with the Fleurs Synthesis Telescope show that PKS2048 – 57, the radio source associated with IC 5063, is asymmetric with the stronger component located at the nucleus of IC 5063 and the weaker component 4.3 arcmin west. Both sources show a slight extension towards each other, but the physical association is not truly convincing. An AAT direct plate copied in two different ways shows (a) a network of dust lanes lying in what could be a warped disc and (b) an extended outer region with very faint symmetric ‘arms’ reminiscent of tidal distortions. A discussion is given of the phenomenon of warped discs in ellipsoidal galaxies.