Morphological decomposition of TNG50 galaxies: methodology and catalogue

We present MORDOR (MORphological DecOmposeR), a new algorithm for structural decomposition of simulated galaxies based on stellar kinematics. The code measures the properties of up to five structural components (a thin/cold and a thick/warm disc, a classical and a secular bulge, and a spherical stellar halo), and determines the properties of a stellar bar (if present). A comparison with other algorithms presented in the literature yields overall good agreement, with MORDOR displaying a higher flexibility in correctly decomposing systems and identifying bars in crowded environments (e.g. with ongoing fly-bys, often observable in cosmological simulations). We use MORDOR to analyse galaxies in the TNG50 simulation and find the following: ( i ) the thick disc component undergoes the strongest evolution in the binding energy-circularity plane, as expected when disc galaxies decrease their turbulent-rotational support with cosmic time; ( ii ) smaller galaxies (with stellar mass, 10 ^9 < M ∗/ Msun<≤5 ×10 9 ) undergo a major growth in their disc components after z ∼1, whereas (iii) the most massive galaxies (5 ×10 10 < M ∗/ M sun≤5 ×10 11 ) evolve to wards more spheroidal dominated objects down to z = 0 due to frequent gravitational interactions with satellites; (iv) the fraction of barred galaxies grows rapidly at high redshift and stabilizes below z ∼2, except for the most massive galaxies that show a decrease in the bar occupation fraction at low redshift; ( v) galaxies with M ∗∼10 11 Msun exhibit the highest relative occurrence of bars at z = 0, in agreement with observational studies. We publicly release MORDOR and the morphological catalogue of TNG50 galaxies.