What is an Active Galaxy?
For our purposes we operationally define an active galaxy to be one in which signs of qualitatively unusual and quantitatively energetic activity (i.e. activity not associated with the evolution of normal stars) are clearly visible and can be connected directly or indirectly to the nucleus. Excluded are simple interacting pairs in which no other signs of abnormalities appear and many emission-line or infrared galaxies, which can be entirely explained as multiple H II regions and/or supernova remnants (French 1980, French & Miller 1981, Weedman 1977a, Weedman et al. 1981). M82 and many other Irr II galaxies may be examples of this last class of interesting but, by our criteria, “inactive” galaxies. A quantitative definition of what constitutes an active galaxy is perhaps not very useful, since galaxies showing low-level nuclear activity (e.g. Heckman 1980b, Stauffer 1981, Hawley & Phillips 1980) may be in a pre- or post- eruptive stage, and so may yield valuable clues into the origin an
