Uncertainties in Galaxy Rotation Curves
  Assessing the likelihood that the rotation curve of a galaxy matches
predictions from galaxy formation simulations requires that the uncertainties
in the circular speed as a function of radius derived from the observational
data be statistically robust. Few uncertainties presented in the literature
meet this requirement. In this paper we present a new standalone tool, makemap,
that estimates the fitted velocity at each pixel from Gauss-Hermite fits to a
3D spectral data cube, together with its uncertainty obtained from a modified
bootstrap procedure. We apply this new tool to neutral hydrogen spectra for 18
galaxies from the THINGS sample, and present new velocity maps with
uncertainties. We propagate the estimated uncertainties in the velocity map
into our previously-described model fitting tool DiskFit to derive new rotation
curves. The uncertainties we obtain from these fits take into account not only
the observational errors, but also uncertainties in the fitted systemic
velocity, position of the rotation centre, inclination of the galaxy to the
line of sight, and forced non-circular motion. They are therefore much
better-defined than values that have previously been available. Our estimated
uncertainties on the circular speeds differ from previous estimates by factors
ranging up to of five, being smaller in some cases and larger in others. We
conclude that kinematic models of well-resolved HI datasets vary widely in
their precision and reliability, and therefore potentially in their value for
comparisons with predictions from cosmological galaxy formation simulations.
