The Amorphous Galaxy NGC 2777: H [CSC]i[/CSC] Evidence for Tidal Interaction with a Faint Companion

Abstract

NGC 2777 is an amorphous galaxy possessing the classic signature of an A-type spectrum with superposed emission lines. There is no optical evidence for an interaction, but observations of the neutral hydrogen in this system reveal an H I bridge between NGC 2777 and U3, a companion that is 3 mag fainter. Far-infrared observations indicate that the current rate of massive star formation in NGC 2777 is low, but the optical spectra indicate that it must have been significantly higher in the recent past. We were unable to detect CO in either galaxy. We also consider a sample of 10 amorphous galaxies, all showing A-type absorption spectra: nine from the Revised Shapley-Ames Catalog, plus NGC 2777. All show optical/H I interaction and/or peculiar velocity fields, supporting the view that amorphous characteristics are the result of interaction. For some of the galaxies, the interacting companion is much fainter than the amorphous system, which indicates that previous concerns raised by the existence of isolated amorphous galaxies may have been premature.