HI Absorption in 3C 293, with MERLIN

  3C 293 is a relatively low redshift and moderately large radio galaxy with a steep-spectrum core at a redshift of ~0.045 (D=180 Mpc) and 1 arcsecond=815 pc. It is associated with a peculiar elliptical galaxy, VV5-33-12, with extensive dust lanes. These filamentary dust lanes are clearly observed in HST images to wind and split as they cross the central region of the source at a P.A. of ~35 degrees. Wider field optical images show a nearby companion galaxy ~37 arcseconds (~30 kpc) away.
  For more information see Beswick,Pedlar & Holloway, 2001 in press MNRAS

The image below shows a false colour HST WFPC2 image of the radio galaxy 3C 293 along with an overlayed (similar angular resolution) MERLIN 1.4 GHz radio image. Selected spectra showing HI absorption across the central few kiloparsecs of this source.

  The extensive HI absorption oberved with MERLIN can be converted into optical depth maps of HI. Below a false colour map of optical depth (blues equaling areas of highest opacity and white lowest) shows the distribution of HI gas in front of the sub-arcsecond radio continuum in 3C 293. Note the approximately vertical stripes of highest opacity are spatially coincident with the winding dust lanes seen in the HST image above.

  Postion Velocity diagram of HI optical depth in front of the AGN in 3C 293. Two distinct velocity gradients are clearly visible in this position velocity diagram which are both centered upon component B (coincident with the position of the AGN). The inner rotating ring is far more distinct and has a radius of just 600pc. Assuming an appropriate orientation for this inner rotating ring a dynamical mass of M(<600 pc)<3.9*10^9 solar masses can be derived.