  We numerically model experiments on the superfluid critical velocity of an
elongated, harmonically trapped Bose-Einstein condensate as reported by [P.
Engels and C. Atherton, Phys. Rev. Lett. 99, 160405 (2007)]. These experiments
swept an obstacle formed by an optical dipole potential through the long axis
of the condensate at constant velocity. Their results found an increase in the
resulting density fluctuations of the condensate above an obstacle velocity of
$v\approx 0.3$ mm/s, suggestive of a superfluid critical velocity substantially
less than the average speed of sound. However, our analysis shows that the that
the experimental observations of Engels and Atherton are in fact consistent
with a superfluid critical velocity equal to the local speed of sound. We
construct a model of energy transfer to the system based on the local density
approximation to explain the experimental observations, and propose and
simulate experiments that sweep potentials through harmonically trapped
condensates at a constant fraction of the local speed of sound. We find that
this leads to a sudden onset of excitations above a critical fraction, in
agreement with the Landau criterion for superfluidity.
