NGC 4365

Background

NGC 4365 was discovered by German-English astronomer William Herschel on April 13, 1784. It has a morphological classification of E3, indicating a slightly flattened elliptical galaxy with an ellipticity of 0.26. The galaxy exhibits a smooth luminosity profile with no indication of dust arms and a shallow cusp at the center. A stream of globular clusters connects NGC 4365 to the neighboring compact lenticular galaxy NGC 4342, suggesting that NGC 4365 is stripping globular clusters and stars from its smaller neighbor via tidal interaction.

The galaxy has a kinematically distinct core region that rotates at right angles to the rest of the galaxy. Most of the galaxy rotates around the major axis with peak velocity reaching around , whereas within of the center the peak velocity is around the minor axis.

This core region is more flattened than the galaxy as a whole, forming a bar-like structure. The stellar populations suggest the galaxy underwent star formation at an early age, with residual gas exhausted about 12 billion years ago. Many of its globular clusters appear to be of intermediate age (2–8 billion years old), though they may instead be of higher than expected metallicity.

The galaxy retains a triaxial structure that has remained largely unchanged for 12 billion years. Because supermassive black holes tend to scatter stars into chaotic new orbits, the longevity of NGC 4365's triaxial structure and kinematically distinct stellar populations indicates it cannot have a supermassive black hole with a mass greater than . The M–sigma relation predicts a SMBH mass of for NGC 4365.