NGC 3991/4/5

The galaxy triplet NGC 3991/4/5, in a color-composite CCD image from the Lowell Observatory 1.1m Hall telescope. NGC 3995, at left (east), has the distinction of being the bluest galaxy in the Second Reference Catalog, as well as of being termed a supergiant compact galaxy by Vorontsov-Velyaminov (this kind of thing can happen if you define compactness with a surface-brightness rather than size criterion). NGC 3991 is the shred-like string of star-forming regions at the northwest corner, and NGC 3994 is the spiral with an internal ring of star-forming region at the southern end of this little grouping. NGC 3995 is also distinguished by having an extraordinarily small rotation velocity - if it is really a disk seen almost edge-on, it has only one tenth of our galaxy's rotation speed. This more likely means that it has been so tidally disturbed by an encounter with NMGC 3994 that much of its material is in radial rather than circular motion; it really is cigar-shaped in this case.

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