A fully cosmological model of a Monoceros-like ring
  We study the vertical structure of a stellar disk obtained from a fully
cosmological high-resolution hydrodynamical simulation of the formation of a
Milky Way-like galaxy. At the present day, the disk's mean vertical height
shows a well-defined and strong pattern, with amplitudes as large as 3 kpc in
its outer regions. This pattern is the result of a satellite - host halo - disk
interaction and reproduces, qualitatively, many of the observable properties of
the Monoceros Ring. In particular we find disk material at the distance of
Monoceros ($R \sim$ 12-16 kpc, galactocentric) extending far above the mid
plane ( 30$^{\circ}$, $\langle Z \rangle \sim$ 1-2 kpc) in both hemispheres, as
well as well-defined arcs of disk material at heliocentric distances $\gtrsim
5$ kpc. The pattern was first excited $\approx 3$ Gyr ago as an $m=1$ mode that
later winds up into a leading spiral pattern. Interestingly, the main driver
behind this perturbation is a low-mass low-velocity fly-by encounter. The
satellite has total mass, pericentre distance and pericentric velocity of $\sim
5\%$ of the host, $\sim 80$ kpc, and 215 km/s, respectively. The satellite is
not massive enough to directly perturb the galactic disk but we show that the
density field of the host dark matter halo responds to this interaction
resulting in a strong amplification of the perturbative effects. This
subsequently causes the onset and development of the Monoceros-like feature.
