Orbital structure evolution in self-consistent N-body simulations

Abstract

ABSTRACT The bar structure in disc galaxies models is formed by different families of orbits; however, it is not clear how these families of orbits support the bar throughout its secular evolution. Here, we analyse the orbital structure on three stellar disc N-body models embedded in a live dark matter halo. During the evolution of the models, discs naturally form a bar that buckles out of the galactic plane at different ages of the galaxy evolution generating boxy, X, peanut, and/or elongated shapes. To understand how the orbit families hold the bar structure, we evaluate the orbital evolution using the frequency analysis on phase space coordinates for all disc particles at different time intervals. We analyse the density maps morphology of the 2:1 family as the bar potential evolves. We showed that the families of orbits providing bar support exhibit variations during different stages of its evolutionary process, specifically prior to and subsequent to the buckling phase, likewise in the secular evolution of the bar. The disc-dominated model develops an internal boxy structure after the first Gyr. Afterwards, the outer part of the disc evolves into a peanut-shape, which lasts till the end of the simulation. The intermediary model develops the boxy structure only after 2 Gyr of evolution. The peanut shape appears 2 Gyr later and evolves slowly. The halo-dominated model develops the boxy structure much later, around 3 Gyr, and the peanut morphology is just incipient at the end of the simulation.