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A significant fraction of barred spiral galaxies exhibits peanut/X-shapedstructures in their central regions. Bars are known to rotate with a singlepattern speed, and they eventually slow down over time due to the dynamicalfriction with the surrounding dark matter halo. However, the nature of thedecay in pattern speed values and whether all peanut bars rotate with a singlepattern speed remain to be investigated. Using N-body simulation of acollisionless stellar disc, we study the case of a long bar with athree-dimensional peanut structure prominent in both edge-on and face-onprojections. We show that such a bar possesses three distinct peaks in the m=2Fourier component. Using the Tremaine-Weinberg method, we measure the patternspeeds and demonstrate that the three regions associated with the three peaksrotate with different pattern speeds. The inner region, which is the core ofthe peanut, rotates slower than the outer regions. In addition, the patternspeed of the inner bar also decays faster than the outer bar with a decaytimescale of 4.5 Gyr for the inner part and ~12.5 Gyr for the outer parts. Thisis manifested as a systematic offset in density and velocity dispersion mapsbetween the inner and outer regions of the long peanut bar. We discuss theimportance of our findings in the context of bar dynamics.

Multiple pattern speeds in a long peanut-shaped bar in a simulated galaxy