Evidence for shock‐heated gas in the Hopkins ultraviolet telescope spectrum of NGC 1068

Far‐ultraviolet spectra of the Seyfert 2 galaxy NGC 1068 obtained with the Hopkins Ultraviolet Telescope during the flight of Astro‐1 aboard the space shuttle Columbia in December 1990 reveal strong emission lines of C III λ977, N III λ991, Lyβ, O VI λλ1032,1038, and He II λ1085. Longward of Lyα the spectrum is similar to previous observations obtained with the IUE. A flat, blue continuum is observed down to the Lyman limit imposed by interstellar absorption in our own Galaxy. The strong C II λ977 and N III λ991 emission is unusual for an AGN, and the line ratios below Lyα are similar to those seen in HUT observations of the Cygnus Loop supernova remnant. Line ratios of C III] λ1909 to λ977 and N III] λ1750 and λ991 imply temperatures exceeding 25500 K and 61000 K, respectively. Since these temperatures are much higher than those typically encountered in photoionized gas, we suggest that shock heating should be re‐considered as an additional source of emission lines in the nucleus of NGC 1068.