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1. INTROUCTION

It is frequently the case that revolutionary scientific ideas are first proposed and then remain dormant for years, or sometimes decades, before their importance is truly appreciated. Often, the reawakening of interest is driven by new technological developments. Such was, for instance, the case of supermassive black holes (SBHs) in galactic nuclei. By the mid 1960s, just a few years after the discovery of QSOs, it was generally recognized that their energy source must be gravitational in nature. Yet for the following three decades the existence of SBHs was destined to be surrounded by skepticism. By the mid 1990s, a few years after the launch of the Hubble Space Telescope, it was widely accepted. Today, it is generally agreed upon that SBHs play a fundamental role in the formation and evolution of their host galaxies. Freed from the burden of having to demonstrate the very existence of supermassive black holes, we can now begin asking more fundamental questions: how are black holes related to their host galaxies, how did they form, how do they accrete, how do they evolve, and what role do they play in the formation of cosmic structure?

The purpose of this contribution is to review the current status of black hole demographics. I will not address the various techniques that are used to measure black hole masses: excellent discussions can be found in the recent literature (e.g. Kormendy & Richstone 1995; Ho 1999). Neither will I discuss the somewhat tumultuous events that lead to a critical reassessment of the "Magorrian relation" (Magorrian et al. 1998) and its analog for local AGNs (Wandel 1999) since a full description of such events can be found elsewhere (Merritt & Ferrarese 2001c). Instead, I will revisit the issue of black hole demographics in light of recent advances in the study of high redshift QSOs (section 2), local AGNs (section 3) and local quiescent galaxies (section 4). I will then outline the prospects for future progress (section 5), and discuss what I believe will be the challenges for the years to come.

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