N-body simulations in reconstruction of the kinematics of young stars in the Galaxy

Abstract

We try to determine the Galactic structure by comparing the observed and modeled velocities of OB-associations in the 3 kpc solar neighborhood. We made N-body simulations with a rotating stellar bar. The galactic disk in our model includes gas and stellar subsystems. The velocities of gas particles averaged over large time intervals ($\sim 8$ bar rotation periods) are compared with the observed velocities of the OB-associations. Our models reproduce the directions of the radial and azimuthal components of the observed residual velocities in the Perseus and Sagittarius regions and in the Local system. The mean difference between the model and observed velocities is $\Delta V=3.3$ km s$^{-1}$. The optimal value of the solar position angle $\theta_b$ providing the best agreement between the model and observed velocities is $\theta_b=45\pm5^\circ$, in good accordance with several recent estimates. The self-gravitating stellar subsystem forms a bar, an outer ring of subclass $R_1$, and slower spiral modes. Their combined gravitational perturbation leads to time-dependent morphology in the gas subsystem, which forms outer rings with elements of the $R_1$- and $R_2$-morphology. The success of N-body simulations in the Local System is likely due to the gravity of the stellar $R_1$-ring, which is omitted in models with analytical bars.