  Recent integral field spectroscopic (IFS) surveys have revealed radial
gradients in the optical spectral indices of post-starburst galaxies, which can
be used to constrain their formation histories. We study the spectral indices
of post-processed mock IFS datacubes of binary merger simulations, carefully
matched to the properties of the MaNGA IFS survey, with a variety of black hole
feedback models, progenitor galaxies, orbits and mass ratios. Based on our
simulation sample, we find that only major mergers on prograde-prograde or
retrograde-prograde orbits in combination with a mechanical black hole feedback
model can form galaxies with weak enough ongoing star formation, and therefore
absent H$\alpha$ emission, to be selected by traditional PSB selection methods.
We find strong fluctuations in nebular emission line strengths, even within the
PSB phase, suggesting that H$\alpha$ selected PSBs are only a subsample of the
underlying population. The global PSB population can be more robustly
identified using stellar continuum-based approaches. The difficulty in
reproducing the very young PSBs in simulations potentially indicates that new
sub-resolution star formation recipes are required to properly model the
process of star formation quenching. In our simulations, we find that the
starburst peaks at the same time at all radii, but is stronger and more
prolonged in the inner regions. This results in a strong time evolution in the
radial gradients of the spectral indices which can be used to estimate the age
of the starburst without reliance on detailed star formation histories from
spectral synthesis models.
