ABSTRACT

It is generally believed that galaxy interactions induce bursts of star formation. We observed a sample of galaxies undergoing different types of interactions in the expectation that the location and nature of the induced star formation could be related to the dynamics of the interaction. We found instead that in almost all galaxies the star formation is concentrated in the nucleus or nuclei, sometimes to a remarkable degree. It appears that extra-nuclear star formation is either difficult to trigger or so short-lived as to be rarely observed. We discuss in detail two galaxies: NGC 5253, site of the most concentrated star formation region yet known, and Arp 30, the exception where star formation is broadly distributed and is seen in both nuclei and in clumps in the bridge connecting them.

INTRODUCTION

Studies of the global properties of large samples of galaxies have shown that interactions between galaxies correlate with bursts of star formation and have lead to the generally accepted belief that interactions can trigger such bursts. Attempts to correlate the local star formation properties of individual galaxies and the interactions they have undergone have been much less successful. We therefore undertook a multiwavelength study of star formation in a sample of interacting or post-interaction galaxies, in the hope of being able to relate the location and type of star formation to the interaction history. The observations include infrared spectra, radio continuum maps, and images in continuum bands, the Wolf-Rayet feature and Hα.