  We describe techniques for measuring the central masses of galaxies using
emission-line kinematics observed with the Hubble Space Telescope. For accurate
results, it is necessary to model various instrumental effects, particularly
the blurring due to the telescope PSF and the width of the spectroscopic
aperture. Observations of nuclear gas disks often reveal substantial internal
velocity dispersions in the gas, suggesting that the disks may be partially
pressure-supported. We also describe a technique for fitting 2-dimensional
spectroscopic data directly in pixel space. This method may be useful for
objects such as M84 that show highly complex and asymmetric line profiles.

Astrophysics