This study aims to make a comparative analysis of galaxy kinematics using IllustrisTNG simulations and integral-field spectroscopy (IFS) observations. We identified 2, 342 early-type galaxies (ETGs) from the TNG100 simulation and 236 ETGs from the TNG50 simulation, to compare with those from the MaNGA and ATLAS ̊m 3D R, ̊m intr) (with the λR parameter measured for edge-on viewing), the cylindrical rotational energy fraction (κ_ ̊m rot), and structural mass ratios such as the spheroid mass fraction (f_ ̊m spheroid) and the stellar halo mass fraction f_ ̊m halo. This study performs a comparative kinematic analysis of ETGs using IllustrisTNG simulations and IFS data from MaNGA and ATLAS ̊m 3D. We demonstrate that standard classifiers—the λ_ R (Rₑ) = 0. 31 ∼ 0. 4, the ratio of rotation energy κ_ relation and coefficient (the higher-order term of the Fourier decomposition of velocity fields) —fail to align with kinematic bimodality. Revised thresholds are proposed: the spin λ_ R, intr ̊m rot ∼ 0. 5, and the mass fraction of a spheroid component f_ ̊m spheroid ∼ 0. 6. It provides a universal threshold that classifies all galaxy types into rotation-dominated (fast rotators) and random motion-dominated (slow rotators) cases. Scaling relations derived from TNG enable estimating κ_̊m rot and f_̊m spheroid from observations. TNG simulations exhibit a bimodality deficit, characterized by a lack of fast rotators and suppressed λ_ R, intr, attributable to excess galaxies with intermediate rotation and high spheroid or stellar halo mass. A novel method for estimating stellar halo mass fractions from IFS kinematics is introduced, even though significant uncertainties persist.
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