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We present the late-time evolution of m12m, a cosmological simulation of aMilky Way-like galaxy from the FIRE project. The simulation forms a bar afterredshift z = 0.2. We show that the evolution of the model exhibits behaviourstypical of kinematic fractionation, with a bar weaker in older populations, anX-shape traced by the younger, metal-rich populations and a prominent X-shapein the edge-on mean metallicity map. Because of the late formation of the barin m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate thebulge, at a level higher than is observed at high latitudes in the Milky Way,implying that its bar cannot have formed as late as in m12m. We also study themodel's vertex deviation of the velocity ellipsoid as a function of stellarmetallicity and age in the equivalent of Baade's Window. The formation of thebar leads to a non-zero vertex deviation. We find that metal-rich stars have alarge vertex deviation (~ 40 degrees), which becomes negligible for metal-poorstars, a trend also found in the Milky Way, despite not matching in detail. Wedemonstrate that the vertex deviation also varies with stellar age and is largefor stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertexdeviation. When we exclude stars that have been accreted, the vertex deviationis not significantly changed, demonstrating that the observed variation ofvertex deviation with metallicity is not necessarily due to an accretedpopulation.

Formation, vertex deviation and age of the Milky Way's bulge: input from a cosmological simulation with a late-forming bar