Infrared and optical maps, (matched in scale for each source; north is up and east is to the left), of the four SMS4 sources detected by Swift-XRT in our sample, centered at the coordinates of the X-ray detections. Infrared maps (left side of each panel) in the W1 filter (3.4 μm) are from AllWISE, while optical maps (right side) in the r filter are from DSS2. Blue ellipses mark the G4Jy positional uncertainty regions. Black solid circles mark the positional uncertainty of the X-ray sources, given at a 90% confidence level, while dashed circles mark the radio/X-ray positional match region at a 95% confidence level. Crosses (x) and plus signs (+) mark infrared sources from AllWISE and optical sources from GSC 2.4.2. Black or white are equally used for AllWISE and GSC 2.4.2 sources to improve the visibility with respect to the map in the background. Green is used for AllWISE counterparts also associated by W20, and for the optical counterparts suggested by BH06.