Luminous Seyfert galaxies have turned up as members of two types of morphologically selected samples of galaxies. Zwicky identified blue compact galaxies as a distinct morphological type, and many of these turned out to be high-luminosity Seyfert galaxies. On the basis of spectroscopic and morphological considerations, these are ``almost QSOs''. For example, the compact blue galaxies II Zw 136 = 2130+099 (the 136th entry in Zwicky's second catalog) and I Zw 1 = 0051+124 have absolute B magnitudes M_B -21.53 + 5 log h₀ and M_B -21.80 + 5 log h₀, respectively, which by the modern definition fall into the QSO class.

Adapted from B.M. Peterson An Introduction to Active Galactic Nuclei, Cambridge University Press, (1997)