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1.1. Demographics

In order to properly access the prevalence of LLAGN, LINER and starburst activity, it is necessary to perform a careful survey of nearby galaxies in which the galactic light is subtracted from the nuclear spectrum in order for the often-weak optical emissions line to be detected. Such as survey was recently completed by Ho, Filippenko & Sargent (1997). The demographics of these types of activity is shown in Figure 1. Clearly, ``low-activity'' galaxies (starburst, LINER, and LLAGN, and transition nuclei containing both LLAGN and starburst emission), 86% of the total, dominate over ``normal'' galaxies. Furthermore, ``normal'' AGN only comprise ~ 10% of all galaxies (Ho, Filippenko, & Sargent 1997). This emphasizes the importance of studying these types of galaxies: the usual state of affairs is for a galaxy to exhibit starburst or LLAGN activity (or both) in its nucleus, and most AGN in the local universe are in a low-luminosity state.

Figure 1

Figure 1. Demographics of activity in nearby galaxies.