NGC 2442: Tidal Encounters and the Evolution of Spiral Galaxies

Using imaging Fabry-Perot data, we study the star-forming properties andkinematics of the nearby barred spiral galaxy NGC 2442. The Halpha emission isvery localized along the strong spiral arms of the galaxy, and shows a markedasymmetry between the sharp, well-defined northern tidal arm and the weakersouthern arm. The velocity field appears highly distorted, with a rapidlyrotating nuclear component. We find evidence for strong non-circular motionsalong the northern arm, coincident with the pronounced dust lane and regions ofintense star formation. The strong asymmetries, disturbed velocity field, andpresence of a perturbed companion suggest that we are witnessing a strongkinematic response to a close interaction, which has redistributed the starformation activity throughout the disk of NGC 2442. Dynamical modeling supportsthis hypothesis, and suggests that the regions of strongest star formation arecoincident with strong shocks occurring along the perturbed northern arm.Despite this redistribution of gas on small scales, this galaxy does not show asignificant departure from the Tully-Fisher relation, nor does it appear to beexperiencing any strong starburst. Moreover, our models predict that in a few x10^8 years, NGC 2442 will have recovered from this encounter and willexperience another passage -- and ultimately a merger -- in a few Gyr. Giventhe environment of many disk galaxies, this tidal encounter cycle seems likelyto be a normal phase of disk galaxy evolution.