Morphological decomposition of TNG50 galaxies: methodology and catalogue

TL;DR

This paper introduces MORDOR, a new algorithm for detailed structural decomposition of simulated galaxies, applied to TNG50 data, revealing galaxy evolution patterns, bar formation, and morphological trends across cosmic time.

Contribution

The paper presents MORDOR, a flexible and accurate algorithm for galaxy structural decomposition, and provides a comprehensive morphological catalogue for TNG50 galaxies.

Findings

Thick disc components evolve significantly over cosmic time.

Smaller galaxies grow their discs after redshift 1.

Massive galaxies become more spheroidal due to interactions.

Abstract

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, $10^{9} \lesssim M_{*} / {\rm M_{\odot}} \leq 5 \times 10^{9}$) undergo a major growth in their disc components after $z\sim 1$, whereas ($iii$) the most massive galaxies ($5 \times 10^{10} < M_{*} / {\rm M_{\odot}} \leq 5\times10^{11}$) evolve toward 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 $z\sim 2$, except for the most massive galaxies that show a decrease in the bar occupation fraction at low redshift; ($v$) galaxies with $M_{*} \sim 10^{11}~{\rm M_{\odot}}$ 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.