Exploring the origin of thick disks using the NewHorizon and Galactica simulations

Understand

Ever since a thick disk was proposed to explain the vertical distribution of the Milky Way disk stars, its origin has been a recurrent question.

• We aim to answer this question by inspecting 19 disk galaxies with stellar mass greater than $10^{10}\,\rm M_\odot$ in recent cosmological high-resolution zoom-in simulations: Galactica and NewHorizon.
• The thin and thick disks are reasonably reproduced by the simulations with scale heights and luminosity ratios as observed.
• We then spatially classify the thin and thick disks and find that the thick disk stars are older, metal-poorer, kinematically-hotter, and higher in accreted star fraction, while both disks are dominated by the stars formed in situ.