Non-Gaussian Error Distributions of Galactic Rotation Speed Measurements
  We construct the error distributions for the galactic rotation speed
($\Theta_0$) using 137 data points from measurements compiled in De Grijs et
al. (arXiv:1709.02501), with all observations normalized to the galactocentric
distance of 8.3 kpc. We then checked (using the same procedures as in works by
Ratra et al) if the errors constructed using the weighted mean and the median
as the estimate, obey Gaussian statistics. We find using both these estimates
that they have much wider tails than a Gaussian distribution. We also tried to
fit the data to three other distributions: Cauchy, double-exponential, and
Students-t. The best fit is obtained using the Students-$t$ distribution for
$n=2$ using the median value as the central estimate, corresponding to a
$p$-value of 0.1. We also calculate the median value of $\Theta_0$ using all
the data as well as using the median of each set of measurements based on the
tracer population used. Because of the non-gaussianity of the residuals, we
point out that the subgroup median value, given by $\Theta_{med}=219.65$ km/sec
should be used as the central estimate for $\Theta_0$.
