Phase spirals in cosmological simulations of Milky Way-size galaxies
  We study the vertical perturbations in the galactic disc of the Milky
Way-size high-resolution hydrodynamical cosmological simulation named GARROTXA.
We detect phase spirals in the vertical projection $Z- V_{Z}$ of disc's stellar
particles for the first time in this type of simulations. Qualitatively similar
structures were detected in the recent Gaia data, and their origin is still
under study. In our model the spiral-like structures in the phase space are
present in a wide range of times and locations across the disc. By accounting
for an evolving mix of stellar populations, we observe that, as seen in the
data, the phase spirals are better observed in the range of
younger-intermediate star particles. We measure the intensity of the spiral
with a Fourier decomposition and find that these structures appear stronger
near satellite pericenters. Current dynamical models of the phase spiral
considering a single perturber required a mass at least of the order of
10$^{10}$ M$_\odot$, but all three of our satellites have masses of the order
of $\sim$10$^8$ M$_\odot$. We suggest that there are other mechanisms at play
which appear naturally in our model such as the physics of gas, collective
effect of multiple perturbers, and a dynamically cold population that is
continuously renovated by the star formation Complementing collisionless
isolated N-body models with the use of fully-cosmological simulations with
enough resolution can provide new insights into the nature/origin of the phase
spiral.
