The HI Kinematics of NGC 4013: a Steep and Radially Shallowing
  Extra-planar Rotational Lag
  NGC 4013 is a distinctly warped galaxy with evidence of disk-halo activity.
Through deep HI observations and modeling we confirm that the HI disk is thin
(central exponential scale height of with an upper limit of 4" or 280 pc), but
flaring. We detect a vertical gradient in rotation velocity (lag), which
shallows radially from a value of -35 +7/-28 km/s/kpc at 1.4' (5.8 kpc), to a
value of zero near R_25 (11.2 kpc). Over much of this radial range, the lag is
relatively steep. Both the steepness and the radial shallowing are consistent
with recent determinations for a number of edge-ons, which have been difficult
to explain. We briefly consider the lag measured in NGC 4013 in the context of
this larger sample and theoretical models, further illuminating disk-halo
flows.
