A radio study of neutral gas and dust in the radio galaxy 3C 293

Abstract

We have observed broad HI absorption in the radio galaxy 3C 293 using Multi-Element Radio Linked Interferometric Network (MERLIN) at 0.2-arcsec angular resolution and the Giant Meterwavelength Radio Telescope (GMRT) at arcsec resolution. Extensive HI is found in absorption across the centre of this peculiar radio galaxy, allowing a detailed study of the dynamics of the neutral gas on linear scales down to ~160pc. In optical depth position-velocity diagrams across the central few kpc we detect a distinct velocity gradient of 179kms^-1arcsec^-1 associated with the broad absorption. This is interpreted as a ring of neutral gas rotating around the suspected position of the active galactic nucleus (AGN). The radius of this high velocity gradient ring is found to be >0.74arcsec (600pc), implying an upper limit upon the enclosed mass of 3.9×10⁹(sin^-2i)M_solar, assuming a near edge-on disc with an inclination of i. The optical depth of HI is mapped across the entire central region of 3C 293 showing enhancements of a factor of 4 in the areas that are co-spatial with dust lanes seen in Hubble Space Telescope (HST) imaging of this galaxy.