Complex sentence: The two galaxies are listed in the "Atlas of Peculiar Galaxies" as one of several prominent examples of a spiral galaxy with a companion galaxy, and the system was also the subject of very early theoretical investigations into galaxy interactions.
Split into simpler sentences: The two galaxies are listed in the "Atlas of Peculiar Galaxies" as one of several prominent examples of a spiral galaxy with a companion galaxy. The system was also the subject of very early theoretical investigations into galaxy interactions.