Stellar Populations in a semi-analytic model I: bulges of Milky Way-like
  galaxies
  We study the stellar populations of bulges of Milky Way-like (MW-like)
galaxies with the aim of identifying the physical processes involved in the
formation of the bulge of our Galaxy. We use the semi-analytic model of galaxy
formation and evolution SAG adapted to this aim; this kind of models can trace
the properties of galaxies and their components like stellar discs, bulges and
halos, but resolution limits prevent them from reaching the scale of stellar
populations (SPs). Properties of groups of stars formed during single star
formation events are stored and tracked in the model and results are compared
with observations of stars in the galactic bulge. MW-like galaxies are selected
using two different criteria. One of them considers intrinsic photo-metric
properties and the second is focused on the cosmological context of the local
group of galaxies (LG). We compare our model results with spectroscopic and
photometric stellar metallicity distributions. We find that 87% of stars in
bulges of MWtype galaxies in our model are accreted and formed in starbursts
during disc instability events. Mergers contribute to 13% of the mass budget of
the bulge and are responsible for the low metallicity tail of the distribution.
Abundance ratios of {\alpha} elements with respect to iron, [{\alpha}/Fe], are
measured in SPs of model galaxies. The patterns found in the model for SPs with
different origins help to explain the lack of a gradient of [{\alpha}/Fe]
ratios in observed stars along the minor axis of the bulge.
