HUT Observations of the Lyman Limit in AGN: Implications for Unified   Models
  We observed a total of 13 low-redshift AGN with the Hopkins Ultraviolet Telescope (HUT) during the course of the Astro-1 and Astro-2 missions. Of these, 4 show intrinsic Lyman limit absorption---NGC 1068, NGC 4151, NGC 3516 and NGC 3227. All galaxies with optically thick Lyman limits have extended narrow-line regions with bi-polar morphologies. All AGN with no absorption are Seyfert 1's with compact NLR's. These observations support geometrical shadowing as the means for collimating the ionizing radiation in unified models of AGN, most likely in a photoionized atmosphere above the obscuring torus. 
G. Kriss, J. Krolik, J. Grimes, Z. Tsvetanov, B. Espey, W. Zheng, and   A. Davidsen