A Warp in Progress: H I and Radio Continuum Observations of the Spiral NGC 3145

VLA HI observations and.6 cm radio continuum observations are presented of the barred-spiral galaxy NGC 3145. In optical images NGC 3145 has stellar arms that appear to cross, forming "X"-features. Our radio continuum observations rule out shock fronts at three of the four "X"-features, and our H I data provide evidence of gas motions perpendicular to the disk of NGC 3145. In large portions of NGC 3145, particularly in the middle-to-outer disk, the HI line profiles 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 (similar to 40 km s(-1)) toward 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 on the northeastern side of NGC 3145; the velocity of the branch is similar to 150 km s(-1) greater than the spiral arm where they appear to intersect in projection. The other is the arm on the southwestern side that forms three of the "X"-features. It differs in velocity by similar to 56 km s(-1) from that of the disk at the same projected location. HI observations are presented also of the two small companions NGC 3143 and PGC 029578. Based on its properties (enhanced SFR, HI emission 50% more extended on its northeastern side, etc.), 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.