Gas Disks and Supermassive Black Holes in Nearby Radio Galaxies

light on the detector to have more than one peak, leading to potentially misleading
phenomena in the velocity profiles. The effects become more pronounced if the slit is
not well aligned with a kinematic axis.
Features due to the effects that Maciejewski & Binney (2001) describe are clearly
present in the closest examples that we observed: M84 and M87. In M87 two obser-
vations were made offset by ∼ 0.1 pixels, which produced very different features in
the spectral rows closest to the nucleus (Figure 4.20). This highlights two problems:
(i) that it is essential to know the location of the center of the galaxy, on smaller
scales than the size of the spectroscopic slit, and (ii) fine details in flux weighting
the observed velocities through the PSF may make large differences to the modeled
velocity profiles - especially in nearby cases.
We tested the effects of varying the mass to light ratio (Υ), axis ratio (q ′ ) and
inclination angle (i) for two representative galaxies: NGC 193 (Figure 4.21) and
NGC 4335 (Figure 4.22). It is clear from those figures that the sensitivity to these
parameters is quite low, particularly in the central region where we expect the models
to best match the gas velocity profiles. Outside of the central region more variation
is apparent, but this is generally smaller than the point-to-point variations in the
velocity profile, so would not influence any conclusions drawn from these data and
160