Optical images of 4C12.50 from the Hubble Space Telescope, previously presented by Batcheldor et al. (2007) and Dasyra et al. (2011). The crosses mark the location of the peak continuum emission in the ALMA band 3 data. The same applies to all following figures with the crosses. Upper left: gas emission comprising primarily [O III] emission with potential contribution from H_β. The image was created from the subtraction of a Hubble Space Telescope ACS image at 5092 Å (filter FR459M) from an ACS image at 5580 Å (filter F550M). Upper right: continuum emission at 5092 Å (filter FR459M). Lower left: H_α and continuum emission (filters FR647M at 6616 Å). Lower right: residual image originating from the subtraction of galactic component models (i.e., a bulge and two disks) from an optical Hubble Space Telescope image of H_α and 5900 Å continuum emission (Batcheldor et al. 2007) using GALFIT (Peng et al. 2002). The subtraction method was described in detail in Dasyra et al. (2011). Its purpose was to bring up any structures underlying the bright regular emission.