The morphological classification of NGC 5665 is unclear and differs by author.[5] In the De Vaucouleurs system it was classified as SAB(rs)c pec?,[6] which indicates a weakly-barred spiral galaxy (SAB) with a transitional inner ring structure (rs), loosely wound spiral arms (c), and suspected peculiarities (pec?). The galactic plane is inclined at an angle of 53°±5° to the plane of the sky,[3] with the major axis aligned along a position angle of 145°.[5]
Evidence suggests that NGC 5665 underwent a gravitational interaction with another galaxy some 500 million years ago, swallowing a smaller companion.[5] It is somewhat asymmetrical in appearance,[6] retaining a single main spiral arm and the remains of several others. The galaxy is rich in dust and gas with a small bar at the center. There are numerous sites of star formation in the arm that match the age of the interaction.[5] The spectrum of the core is a blend between a LINER and an H II region.[6]
^ abcdThomas, H. C.; Dunne, L.; Clemens, M. S.; Alexander, P.; Eales, S.; Green, D. A. (February 2002), "The distribution of atomic gas and dust in nearby galaxies - I. Presentation of matched-resolution VLA H I and SCUBA 850-μm maps", Monthly Notices of the Royal Astronomical Society, 329 (4): 747–758, Bibcode:2002MNRAS.329..747T, doi:10.1046/j.1365-8711.2002.05035.x.
