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Paper: Structure and Gas Dynamics in the Central 100 pc of a Powerful LINER Galaxy
Volume: 249, The Central Kiloparsec of Starbursts and AGN: the La Palma Connection
Page: 298
Authors: Dressel, L. L.; Gallagher, J. S.
Abstract: NGC 3998 is an S0 galaxy with an exceptionally bright LINER nucleus and a powerful milliarcsec-scale radio jet. HST images reveal a bright compact disk of ionized gas within the central arcsec. We have used STIS to make long-slit observations of the Hα, [N ii], and [S ii] emission of this disk in five parallel slices. The gas velocities rise sharply inward, revealing a black hole, but also rise outward beyond the sphere of influence of the black hole, indicating the density of the surrounding matter. We have compared the line profiles to simulated observations of disks rotating in selected gravitational potentials to measure the black-hole mass and the surrounding density. The modeled density profiles can be compared to the light profile we have measured with a combination of HST and WIYN imaging. The interpretation of the high central velocity dispersion limits the accuracy of the black-hole mass measurement. 2 times 108Modot is a lower limit to the black-hole mass.
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