| Description: | 'BL Lacertae objects' (or 'BL Lacs') are generally low-luminosity radio galaxies with a jet oriented at a small angle to the line-of-sight. Their radio structure can be complex and strongly dependent on the resolution of the observations, as the jets often show large bends or misalignments on scales between tens and thousands of light-years from the central compact "core". This could result from precession of the jet direction, or from interaction between the jet and gas surrounding the active galactic nucleus. High-resolution images at a wavelength of 18cm, made by Gabriele Surcis during his summer studentship at JIVE, are shown here for the BL Lac object thought to be associated with X-ray source WGA J1231+2848. The top right-hand image is from observations using 10 antennas of the EVN. A lower resolution image from simultaneous MERLIN data is shown in the top left panel. An intermediate-resolution image made after carefully combining the data from both arrays is shown in the lower left panel, while the lower right panel shows a plot of the so-called (u,v) coverage, or sampling on all of the projected baselines from the two arrays - the shorter MERLIN baselines occupy the central region, corresponding to larger angular scales on the sky.
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