Reliability and limitations of inferring birth radii in the Milky Way
  disk
  Recovering the birth radii of observed stars in the Milky Way is one of the
ultimate goals of Galactic Archaeology. One method to infer the birth radius
and the evolution of the ISM metallicity assumes a linear relation between the
ISM metallicity with radius at any given look-back time. Here we test the
reliability of this assumption by using 4 zoom-in cosmological hydrodynamic
simulations from the NIHAO-UHD project. We find that one can infer precise
birth radii only when the stellar disk starts to form, which for our modeled
galaxies happens ~ 10 Gyr ago, in agreement with recent estimates for the Milky
Way. At later times the linear correlation between the ISM metallicity and
radius increases, as stellar motions become more ordered and the azimuthal
variations of the ISM metallicity start to drop. The formation of a central bar
and perturbations from mergers can increase this uncertainty in the inner and
outer disk, respectively.
