Stellar population gradients at cosmic noon as a constraint to the
  evolution of passive galaxies
  Context: The radial variations of the stellar populations properties within
passive galaxies at high redshift contain information about their assembly
mechanisms, based on which galaxy formation and evolution scenarios may be
distinguished.
  Aims: The aim of this work is to give constraints on massive galaxy formation
scenarios through one of the first analyses of age and metallicity gradients of
the stellar populations in a sample of passive galaxies at $z > 1.6$ based on
spectroscopic data from the Hubble Space Telescope.
  Methods: We combined G$141$ deep slitless spectroscopic data and F$160$W
photometric data of the spectroscopically passive galaxies at $1.6< z < 2.4$
with $H_{160} < 22.0$ in the field of view of the cluster JKCS $041$. We
extracted spectra from different zones of the galaxies, and we analysed them by
fitting them with a library of synthetic templates of stellar population models
to obtain estimates of the age and metallicity gradients.
  Results: We obtained reliable measurements of age and metallicity parameters
in different spatial zones of $\text{four}$ galaxies. We performed spatially
resolved measurements in individual high-redshift galaxies without the need of
peculiar situations (i.e. gravitational lensing) for the first time. All four
galaxies exhibit negative metallicity gradients. Their amplitude, similar to
that measured in galaxies in the local Universe, suggests that the stellar
populations of passive galaxies from $z \sim 2$ to $z = 0$ are not
redistributed.
  Conclusions: Although the sample we analysed is small, the results we
obtained suggest that the main mechanism that determines the spatial
distribution of the stellar population properties within passive galaxies is
constrained in the first $3$ Gyr of the Universe. This is consistent with the
revised monolithic scenario.
