  We study the galactic bulges in the Auriga simulations, a suite of thirty
cosmological magneto-hydrodynamical zoom-in simulations of late-type galaxies
in Milky Way-sized dark matter haloes performed with the moving-mesh code
AREPO. We aim to characterize bulge formation mechanisms in this large suite of
galaxies simulated at high resolution in a fully cosmological context. The
bulges of the Auriga galaxies show a large variety in their shapes,sizes and
formation histories. According to observational classification criteria, such
as Sersic index and degree of ordered rotation, the majority of the Auriga
bulges can be classified as pseudo-bulges, while some of them can be seen as
composite bulges with a classical component; however, none can be classified as
a classical bulge. Auriga bulges show mostly an in-situ origin, 21 percent of
them with a negligible accreted fraction (facc < 0.01). In general,their
in-situ component was centrally formed, with 75 percent of the bulges forming
most of their stars inside the bulge region at z=0. Part of their in-situ mass
growth is rapid and is associated with the effects of mergers, while another
part is more secular in origin. In 90 percent of the Auriga bulges, the
accreted bulge component originates from less than four satellites.We
investigate the relation between the accreted stellar haloes and the bulges of
the Auriga simulations. The total bulge mass shows no correlation with the
accreted stellar halo mass, as in observations. However, the accreted mass of
bulges tends to correlate with their respective accreted stellar halo mass.
