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Session 25 - Seyfert Galaxies.
Oral session, Wednesday, January 07
Georgetown,
Many active galactic nuclei channel energetic particles into jets that feed powerful extended lobes of radio emission; others remain quite compact. Both classes of active galaxies are suspected to be powered gravitationally by the accretion of surrounding material onto a massive central black hole. The central masses of galaxies can be measured from observations of either the central stars or gas, provided that the gas is sufficiently luminous and in well-ordered motion driven predominantly by gravitational force. The first arcsec-scale well-ordered disk of ionized gas was discovered with WFPC2 on the Hubble Space Telescope in M87 (Ford et al. 1994, Ap.J. 435, L27). As a complement to on-going programs to find more such disks in radio galaxies with jets like M87, we have used WFPC2 to make H\alpha and continuum images of 12 bright Liners with strong compact nuclear radio sources. We have found sub-arcsec scale emission-line disks in all of them. Some of the galaxies also have prominent dust structrures.
We expect to make STIS observations of one or two of the galaxies by the end of 1997. The 0.1 arcsec slit will be placed in 3 or more parallel positions near the major axis of the gaseous disk, with wavelength centered near H\alpha . We will take advantage of the spatial resolution to isolate and examine the broad H\alpha components, already known to exist. We will model the velocity distributions to see if rotation is basically Keplerian, to see if there are departures from simple rotation, and to determine or set limits on the masses of black holes and distributed mass. This research is supported by NASA HST GO grants 5924 and 7354.
