The shape of spiral galaxies

Abstract

In this work we analyze the stellar surface density distribution in the equatorial plane of the disk of a spiral galaxy from a cosmological simulation and its evolution. We apply a Fourier series adjustment that allows us to detect the different internal structures of the galaxy and intuitively interpret them as central bars, spiral arms or lopsidedness. We see that the galaxy has a complex structure, but it is dominated by the first two Fourier modes, giving rise to a central bar and a spiral arm that winds around the galaxy from the middle radii to outwards. These present different rotation frequencies and, in general, their relative amplitudes increase with the passage of time. The cause of this could be the influence of the satellites, the consequence of the deformation of the halo or the result of the gas accretion, but this should be studied more carefully in the future