Bulge formation in MW- and M31-like galaxies

In this talk I will report the results on bulge formation in MW- and M31 like-galaxies obtained from state-of-the-art high-resolution cosmological magneto-hydrodynamical simulations: the Auriga suite and TNG50. We characterise photometric bulges by a Sérsic function in two-component V-band surface brightness decompositions. We show that low-Sérsic bulges are predominant in these types of simulated galaxies. We study the origin of low and high-Sérsic bulges in a sample of ∼300 MW/M31-like galaxies and show that low-Sérsic bulges are predominant in these types of simulated galaxies. Using TNG50, we show that the timing of the last significant merger, and the longevity of a bar, play a significant role in determining the final concentration of bulges. We also show
that the environment, based on the density and number of neighbouring galaxies in which the galaxies reside plays no role on determining the final bulges Sérsic index. Finally, we also characterise bulges kinematically based on stellar particles circularities. We confirm the in-situ origin of kinematic bulges in both simulation suites. Galaxies that host a high-Sérsic photometric bulge present an excess of particles accreted from satellite galaxies in the kinematic bulge. By studying their origin, we also find that a single galaxy accounts for more than 50% of the accreted particles in kinematic bulges, while only a few explain the 90% of this component.