AAS 196th Meeting, June 2000
Session 21. Supermassive Blackhole Research and Advances with STIS
Topical Session Oral, Tuesday, June 6, 2000, 8:30-10:00am, 10:45am-12:30pm, 2:00-3:30pm, 3:45-5:30pm, Lilac Ballroom

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[21.16] Massive Black Holes in Nearby Low-Luminosity AGNs

A. J. Barth (Harvard-Smithsonian Center for Astrophysics)

The occurrence of low-luminosity nuclear activity in nearby galaxies can make it possible to determine the central black hole masses, by measurement of the velocity field of ionized gas in the circumnuclear environment. Moreover, nuclear activity provides added motivation to measure central masses, because the black hole mass is a crucial parameter for models of the accretion flows in low-luminosity AGNs. Five nearby active galaxies have recently been observed with STIS as part of a program to study their narrow-line region kinematics and to determine the central masses. I will present results from this program and discuss some of the difficulties involved in performing gas-dynamical searches for black holes in low-luminosity AGNs.

The incidence of low-luminosity activity can also provide important constraints on the demographics of massive black holes. Optical spectroscopic surveys indicate that approximately 40% of all galaxies can be regarded as ``active'' to some degree. If the origin of this activity can be attributed to accretion onto a massive black hole, then the fraction of galaxies with active nuclei is a lower limit to the fraction of galaxies which contain a massive black hole. However, direct evidence for a nonstellar energy source is often lacking, particularly for the faintest active nuclei. Faint nonstellar continuum sources can be detected in Chandra observations, and future X-ray data may provide the most accurate census of accreting black holes in nearby galactic nuclei.

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