Morphological decomposition of TNG50 galaxies: methodology and catalogue

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, $10^{9} \lesssim M_{*}/~\rm M_{\odot }\le 5 \times 10^{9}$) undergo a major growth in their disc components after z ∼ 1, whereas (iii) the most massive galaxies ($5 \times 10^{10} < M_{*}/~\rm M_{\odot }\le 5\times 10^{11}$) 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 ∼ 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.

Early Results from GLASS-JWST. XVIII. A First Morphological Atlas of the 1 < z < 5 Universe in the Rest-frame Optical

“…Overall, we see strong clues that the Hubble sequence is well developed by z = 1.5. The current generation of cosmological hydrodynamic simulations, such as TNG50 (the highestresolution run of the IllustrisTNG suite), do predict a significant proportion of disks in star-forming galaxies at high redshifts, for instance ∼30% at z ; 3 and ∼50% at z ; 2 for M  10 9.5 M e (Pillepich et al 2019, see their Figure 9), and moreover predict a population of well-developed spirals with bulges at z = 2 visible in rest-frame optical (although this may be sensitive to decomposition morphology; see Zana et al 2022). As additional JWST imaging data becomes available over wider fields, we will be better able to empirically confirm (or challenge) these predictions.…”

Bar formation in submaximal discs: a challenge for ΛCDM

“…The lack of barred galaxies remains clear for M * < 10 10.5 M in TNG50 even when comparing with other observational bar fraction estimates (Oh et al 2012). Note that the measured bar fraction in TNG50 at M * < 10 10.5 M is however higher in Zana et al (2022) than in Roshan et al (2021), but still not quite as high as in Oh et al (2012). Note that Masters et al (2012); Melvin et al (2014) found even smaller observational bar fractions at small masses, as well as an increasing bar fraction with mass in contradistinction with various other studies (Díaz-García et al 2016;Consolandi 2016).…”

The role of impact parameter in typical close galaxy flybys

“…Examining luminous face-on spiral galaxies from the COSMOS survey, Sheth et al (2008) found that the fraction of barred galaxies is highly dependent on the redshift, sharply increasing from ∼20% at z ∼ 0.84 to ∼65% in the local Universe, which was confirmed in cosmological simulations (e.g. Cavanagh et al 2022;Zana et al 2022). Such a high difference cannot be explained by the flybys alone.…”

“…Using a tool for the structural decomposition of galaxies based on stellar kinematics (e.g. MORDOR algorithm, Zana et al, 2022) could help us estimate the amount of transferred mass since the majority of particles associated with the bar would be flagged as a pseudo-bulge component. A strong bar in simulation B30, which accounts for roughly 20% of the total disc mass (or around 30% of the inner disc, where R < 15 kpc), captures up to 6% of the bulge particles.…”