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We investigate the stellar kinematics of a sample of galaxies extracted fromthe hydrodynamic cosmological Magneticum Pathfinder simulations out to $5$half-mass radii. We construct differential radial stellar spin profilesquantified by the observationally widely used $\lambda_\mathrm{R}$ and theclosely related $(V/\sigma)$ parameters. We find three characteristic profileshapes: profiles exhibiting a (i) peak within $2.5$ half-mass radii and asubsequent decrease (ii) continuous increase that plateaus at larger radiitypically with a high amplitude (iii) completely flat behaviour typically withlow amplitude, in agreement with observations. This shows that the kinematicstate of the stellar component can vary significantly with radius, suggesting adistinct interplay between in-situ star formation and ex-situ accretion ofstars. Following the evolution of our sample through time, we provide evidencethat the accretion history of galaxies with decreasing profiles is dominated bythe anisotropic accretion of low mass satellites that get disrupted beyond $\sim 2.0$ half-mass radii, building up a stellar halo with non-ordered motionwhile maintaining the central rotation already present at $z=2$. In fact, at$z=2$ decreasing profiles are the predominant profile class. Hence, we canpredict a distinct formation pathway for galaxies with a decreasing profile andshow that the centre resembles an old embedded disk. Furthermore, we show thatthe radius of the kinematic transition provides a good estimation for thetransition radius from in-situ stars in the centre to accreted stars in thehalo.

Kinematics of Simulated Galaxies II: Probing the Stellar Kinematics of Galaxies out to Large Radii