Taking the Milky Way for a spin: disc formation in the ARTEMIS simulations

Abstract

We investigate the formation (spin-up) of galactic discs in the ARTEMIS simulations of Milky Way-mass galaxies. In almost all galaxies discs spin up at higher [Fe/H] than the Milky Way (MW). Those that contain an analogue of the Gaia Sausage-Enceladus (GSE) spin up at a lower average metallicity than those without. We identify six galaxies with spin-up metallicity similar to that of the MW, which form their discs $\sim 8-11$ Gyr ago. Five of these experience a merger similar to the GSE. The spin-up times correlate with the halo masses at early times: galaxies with early spin-up have larger virial masses at a lookback time $t_L=12$ Gyr. The fraction of stars accreted from outside the host galaxy is smaller in galaxies with earlier spin-ups. Accreted fractions small enough to be comparable to the MW are only found in galaxies with the earliest disc formation and large initial virial masses ($M_{200c}\approx 2\times 10^{11}{M}_{\odot }$ at $t_L=12$ Gyr). We find that discs form when the halo's virial mass reaches a threshold of $M_{200c}\approx (6\pm 3)\times 10^{11}{M}_{\odot }$, independent of the spin-up time. However, the failure to form a disc in other galaxies appears to be instead related to mergers at early times. We also find that discs form when the central potential is not particularly steep. Our results indicate that the MW assembled its mass and formed its disc earlier than the average galaxy of a similar mass.

arXiv comment9 pages, 7 figures, published in MNRAS

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• The dawn of disks: unveiling the turbulent ionised gas kinematics of the galaxy population at $z\sim 4-6$ with JWST/NIRCam grism spectroscopy
• On the metal-poor edge of the Milky Way "thin disc"
• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) II. Unveiling the formation and evolution of the kinematically selected Thick and Thin Discs
• Deciphering the Milky Way disc formation time encrypted in the bar chrono-kinematics
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• Two-phase formation of galaxies: the coevolution between galaxies and dark matter halos