NGC 6776 'The Pentagon' - an old merger?

Abstract

We present photometric and spectroscopic observations of NGC 6776. Photographic and CCD images show that this galaxy has perturbed and chaotic outer isophotes and possesses at least one tidal tail. Spectroscopic observations show that the system is rapidly rotating, with low stellar velocity dispersion, atypical of early-type systems. These characteristics strongly suggest that this galaxy has undergone a merger with a second system. However, the colour distribution shows no evidence for the presence of young stars, while IRAS data indicate that the system is relatively free of dust. We conclude that this galaxy is the remnant of a merger occurring at least 109 yr ago, making it the oldest merger known, and involving at least one dust-poor disc system.