The giant Hα bow shock inflated by the radio jet south–southwest of GGD 27 in a continuum-subtracted image formed by subtracting a scaled SDSS i band image from the narrowband Hα image. The Hα image was obtained using the 78 Å bandpass filter. Dashed arrow marks the orientation and extrapolated location of the radio jet from IRAS 18162-2018. Dashed circles mark the locations of compact Hα knots close to the radio jet axis. See text for details.