On the stellar halo metallicity profile of Milky Way-like galaxies in
  the Auriga simulations
  A recent observational study of haloes of nearby Milky Way-like galaxies
shows that only half (four out of eight) of the current sample exhibits strong
negative metallicity ([Fe/H]) gradients. This is at odds with predictions from
hydrodynamical simulations where such gradients are ubiquitous. In this Letter,
we use high resolution cosmological hydrodynamical simulations to study the
[Fe/H] distribution of galactic haloes. We find that kinematically selected
stellar haloes, including both in-situ and accreted particles, have an oblate
[Fe/H] distribution. Spherical [Fe/H] radial profiles show strong negative
gradients within 100 kpc, in agreement with previous numerical results.
However, the projected median [Fe/H] profiles along the galactic disc minor
axis, typically obtained in observations, are significantly flatter. The median
[Fe/H] values at a given radius are larger for the spherical profiles than for
the minor axis profiles by as much as 0.4 dex within the inner 50 kpc. Similar
results are obtained if only the accreted stellar component is considered
indicating that the differences between spherical and minor axis profiles are
not purely driven by heated disc star particles formed in situ. Our study
highlights the importance of performing careful comparisons between models and
observations of halo [Fe/H] distributions.
