A Warp in Progress: H I and Radio Continuum Observations of the Spiral
  NGC 3145
  We present VLA H I and 6 cm radio continuum observations of the spiral NGC
3145 and H I observations of its two companions, NGC 3143 and PGC 029578. In
optical images NGC 3145 has stellar arms that appear to cross, forming
"X"-features. Our radio continuum observations rule out shock fronts at 3 of
the 4 "X"-features. In the middle-to-outer disk, the H I line-profiles of NGC
3145 are skewed. Relative to the disk, the gas in the skewed wing of the
line-profiles has z-motions away from us on the approaching side of the galaxy
and z-motions of about the same magnitude (about 40 km/s) towards us on the
receding side. These warping motions imply that there has been a perturbation
with a sizeable component perpendicular to the disk over large spatial scales.
Two features in NGC 3145 have velocities indicating that they are out-of-plane
tidal arms. One is an apparent branch of a main spiral arm; the velocity of the
branch is 150 km/s greater than the spiral arm where they appear to intersect
in projection. The other is an arm that forms 3 of the "X"-features. It differs
in velocity by 56 km/s from the disk at the same projected location. Based on
its SFR and H I properties, NGC 3143 is the more likely of the two companions
to have interacted with NGC 3145 recently. A simple analytic model demonstrates
that an encounter between NGC 3143 and NGC 3145 is a plausible explanation for
the observed warping motions in NGC 3145.
