Gas Disks and Supermassive Black Holes in Nearby Radio Galaxies

various sources as quoted in Table 2.1. The sense of the rotation along the major
axis is also a free parameter at this point (whether the velocities go from positive to
negative, or negative to positive across the nucleus). For the majority of our sample
stellar dynamics are not available, and if they were it is not necessarily clear that the
gas closest to the nucleus must as a matter of course be rotating in the same direction
as the stars.
To fit both of these variables, we found the minimum in the signal-to-noise
weighted residuals between the observations and all three of the models, for both
senses of the velocity. In Figures 4.1 to 4.18 we plot these values for various devi-
ations of the recessional velocities from the quoted means and clear minima can be
seen, which we take to be a reliable way of determining the recession velocity. In
Table 4.5 the offset velocities (from the values in Table 2.1) are listed, along with an
indication of the sense of the direction of the rotation.
4.2.6 Sensitivity to parameters
The fit of the disk flux profile F(R) is the most sensitive to numerical noise and
leaves noticeable effects (‘numerical ringing’) in the output velocity profiles when
not properly modeled. We found it necessary to work in double precision for all
calculations at this stage in order to produce numerically stable results. We ran
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