Kinematic scaling of thin and thick discs from SAMI to NewHorizon
Year: 2026
Type: article
Abstract: ABSTRACT We revisit the relation between disc stellar mass and disc velocity dispersion ($M_*$–$\sigma _{\rm e}$) and extend it to thin and thick subcomponents using orbit-based dynamical models of 161 SAMI galaxies and counterpart measurements for 31 disc galaxies in the NewHorizon simulation. On the observational side, we apply Schwarzschild orbit superposition to recover orbital circularity distributions and component kinematics. On the simulation side, we sample thin and thick discs by circularity and, separately, by stellar age to test classification dependence. Our analysis reveals three main results. (1) Discs follow a tight $M_*$–$\sigma _{\rm e}$ relation, nearly parallel to the bulge relation. (2) For both circularity- and age-based definitions, the thick-disc component is systematically hotter than the thin-disc component, and the thin-thick dispersion ratio varies only weakly with mass. However, age cuts yield a smaller kinematic contrast, indicating that stellar age and orbital circularity do not map one-to-one and that no single global age threshold reproduces the circularity-based split. (3) Method and data systematics are present, with Schwarzschild modelling returning slightly higher disc $\sigma _{\rm e}$ than spectroscopic bulge–disc decompositions, and simulated discs showing lower $\sigma _{\rm e}$ at fixed mass than observed. All these results are consistent with a baseline set by vertical-equilibrium scalings, with secular heating accumulating over time and modulating the dispersion at fixed mass. Occasional minor interactions may add localized heating but do not appear to be essential for explaining the qualitative, global trends reported here. Future tests with chemo-dynamical modelling and higher-resolution, chemistry-tracking simulations will provide stronger constraints on disc substructures in external galaxies.
Institutions: Yonsei University, Commonwealth Scientific and Industrial Research Organisation, Australian National University, The University of Sydney, Centre National de la Recherche Scientifique, Institut d'Astrophysique de Paris, Sorbonne Université, Kyung Hee University, Kavli Institute for the Physics and Mathematics of the Universe, International Laboratory for Astrophysics, Neutrino and Cosmology Experiments, The University of Tokyo, ASTRO-3D, ARC Centre of Excellence for All-sky Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W7171045382