SOs with Counter-Rotating Gas: NGC 3941 and NGC 7332

Summary

ABSTRACT

Two SO galaxies with extended counter-rotating [O III] 5007A gas are presented. The first, NGC 3941, is a barred field SO inclined 50° to the line-of-sight. The second, NGC 7332, is an edge-on field SO with a prominent boxy bulge. Multiple stellar components are not obviously present in either object nor do their structures have major distortions. This suggests that the progenitors of the extended emission were low mass dwarf/satellites or tidally stripped material.

INTRODUCTION

Early-type galaxies offer a unique laboratory in which to study galaxy interactions and their effects on the stellar and nonstellar components of the participants. The initial low gas and dust content of the host galaxy and the generally smooth morphology of early-type galaxies facilitates the detection of the perturbing influence of interactions and mergers. Whether these signatures of interaction manifest themselves as starbursts, bars, dust lanes, counter-rotating disks, or other phenomena depends on specifics such as the nature of the secondary object, the parameters of the collision, and the resulting evolution of the material.

The origins of the features displayed by the two objects mentioned here are suggestive of galaxy interactions playing an important role in the evolution of some early-type galaxies. These galaxies join the list (see Bertola et al. 1992) of SO galaxies displaying a decoupling of the angular momentum between their gas and stars.