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Session 10 - Spiral Galaxies.
Display session, Monday, June 10
Amorphous galaxies are a relatively rare morphological type representing about one percent of catalogued galaxies. Several are well known examples of tidal interaction and display extensive HI distortions and streamers. The M82-M81 and the NGC 3077-M81 systems are representative. It is such prominent interaction that has prompted the suggestion that material captured by the soon-to-be amorphous galaxy is responsible for the formation of such systems.
NGC 2777 is an amorphous galaxy of 14th magnitude and is a member of the sparse NGC 2775 Group. It is 11 arcmin distant (55 kpc) from NGC 2775. An Arecibo telescope map of this group (Haynes, AJ 86, 1126, 1981) shows an extension of the HI of NGC 2777. The extension is generally towards NGC 2775 but not quite along the line to it. The latter galaxy is a near face-on Sa system with no apparent HI extension or anomaly. The radial velocities of the two systems differ by 140 km/s.
A recent VLA map of the complex shows that the HI around NGC 2777 is actually extended in the direction of an anonymous galaxy which lies at a distance of about 3.5 arcmin. The presence of this companion is mentioned in the Notes to the UGC. Arp and Sulentic (ApJ,375,569,1991) have discussed the relationship between this object and NGC 2777. Following Arp, we will call this object U3.
The radial velocities of the HI in NGC 2777 and U3 differ by less than 100 km/s. The HI contours at the 20 mJy/beam level in both systems are asymmetric and point to one another along the line connecting their centers. They are clearly interacting and this interaction represents another instance of an amorphous galaxy showing tidal effects in its HI. However, in this instance the more luminous (more massive?) galaxy displays the amorphous characteristics unlike, e.g., M82/M81 and NGC 3077/M81. The character of U3 is unknown, but additional observations of it are in progress.
Program listing for Monday