Oscillations of dark matter halos in galaxies and their effects on motion of stars

Abstract

Matter and dark matter in galaxies represent two main components linked by the gravitational interaction. Collisions of galaxies may create an offset between the centres of mass of these components. Ignoring the internal dynamics of particles in the dark matter halo and the Keplerian rotation of matter in the galaxy, we focus on the possible relative oscillations of the matter component as a whole within the dark matter halo. We estimate the amplitude and frequency of these oscillations assuming that the offset of the centres of mass is small as compared with the size of the galaxy. Such oscillations, if exist, should manifest themselves in anomalies of velocities of stars in the galaxy, such as the density waves and runaway stars which have orbit periods in resonance with oscillations.

Figures (2)

• Figure 1: Time evolution of the vertical ($z$) displacement of circular stellar trajectories initially located at the distance $r_0$ from the galactic centre. Without perturbation, all stars remain in the plane $z=0$; once the perturbation (\ref{['perturbation']}) is activated ($t>0$), the trajectories develop oscillatory vertical motion.
• Figure 2: Deformations of the galactic disc due to oscillating dark matter halo in the direction orthogonal to the disc after $0.7$ Gyr since the periodic dark matter oscillation was introduced. Units are kpc.