Impact of cosmological satellites on the vertical heating of the Milky Way disc

Abstract

We present a high resolution study of the impact of realistic satellite galaxies, extracted from cosmological simulations of Milky Way haloes including 6 Aquarius suites and Via Lactea \rom{2}, on the dynamics of the galactic disc. The initial conditions for the multi-component Milky Way galaxy were generated using the GalIC code, to ensure a system in dynamical equilibrium state prior to addition of satellites. Candidate subhaloes that came closer than 25\,kpc to the centre of the host DM haloes with initial mass enclosed within the tidal radius, $M_\textrm{tid}$ $\ge$ 10$^{8} M_{\odot}$\,=\,0.003 $M_\textrm{disc}$, were identified, inserted into our high resolution N-body simulations and evolved for 2 Gyr. We quantified the vertical heating due to such impacts by measuring the disc thickness and squared vertical velocity dispersion $\sigma_{z}^{2}$ across the disc. According to our analysis the strength of heating is strongly dependent on the high mass end of the subhalo distribution from cosmological simulations. The mean increase of the vertical dispersion is $\sim$ 20\,km$^{2}$\,s$^{-2}$\,Gyr$^{-1}$ for R $>$ 4\,kpc with a flat radial profile while, excluding Aq-F2 results, the mean heating is $<$ 12\,km$^{2}$\,s$^{-2}$\,Gyr$^{-1}$, corresponding to 28\% and 17\% of the observed vertical heating rate in the solar neighbourhood. Taking into account the statistical dispersion around the mean we miss the observed heating rate by more than 3$\sigma$. We observed a general flaring of the disc height in the case of all 7 simulations in the outer disc.