2026/07/21 by Youngmin Baek, Sree Oh, Sukyoung K. Yi +5
#astro-ph.GA
The spin parameter λ_\rmRe is a proxy for the specific stellar angular momentum of galaxies and is a useful metric for classifying kinematic morphology. This study aims to quantify the relative importance of galaxy properties in explaining λ_\rmRe, using data from the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. We apply partial correlation analysis and partial least squares regression to assess the relative contributions of different parameters in explaining λ_\rmRe. We find that morphology indicators, bulge-to-total ratio within one effective radius (B/T_\rme) and ellipticity (ε_\rme), show the strongest correlations with λ_\rmRe and play a leading role in the regression analysis. This result statistically confirms the established fast-rotator sequence, in which fast-rotating early-type galaxies form a continuous structural and kinematic sequence with spiral galaxies, with λ_\rmRe decreasing as bulge prominence increases. The light-weighted age and stellar mass also exhibit significant correlations, but their contributions are secondary to the morphology indicators in multivariate analyses. We also examine whether the observed trends in λ_\rmRe can be reproduced using galaxy properties alone. The morphology indicators (B/T_\rme, ε_\rme) reproduce the overall distribution of observed λ_\rmRe with a scatter of about 0.12, while the inclusion of AgeLW and M_⋆ provides only modest additional improvement. However, these relations do not reproduce the slow-rotator regime well. Overall, our results show that photometric structural parameters best explain λ_\rmRe and suggest that statistical inference of galaxy spin from non-IFS observables may become feasible with improved models and a broader set of parameters.