Dissecting the 3D chemo-dynamical structures of NGC 1381: a galaxy hosting an ancient slow bar with an accreted bulge and thick disc

Author(s): Yunpeng Jin, Ling Zhu, Shude Mao, Marie Martig, Francesca Pinna, Glenn van de Ven, Yuchen Ding
Abstract: We applied the barred population-orbit superposition method developed in \citet{Jin2025a,Jin2025b} to construct 3D chemo-dynamical models for the barred S0 galaxy NGC~1381 in the Fornax cluster. Based on the stellar orbits in the models, we decomposed NGC~1381 into six components: (1) a dynamically warm nuclear disc with $f_{\rm nucl}\sim5\%$; (2) a rigidly rotating, BP/X-shaped bar with $f_{\rm bar}\sim30\%$; (3) a dynamically hot, spheroidal bulge with $f_{\rm bulge}\sim17\%$; (4) a dynamically cold thin disc with $f_{\rm thin}\sim28\%$; (5) a vertically extended thick disc with $f_{\rm thick}\sim16\%$; and (6) a dynamically hot, spatially diffuse stellar halo with $f_{\rm halo}\sim5\%$. The nuclear disc, bar, and thin disc are metal-rich ($[Z/\rm H]\gtrsim0$), $α$-poor ($\rm[Mg/Fe]\lesssim0.2$), and old ($\sim13\rm\,Gyr$), corresponding to in situ formation in the early Universe. The bulge, thick disc, and stellar halo are metal-poor ($[Z/\rm H]\lesssim0$), $α$-rich ($\rm[Mg/Fe]\gtrsim0.2$), and younger than or comparable in age to the in situ components, suggesting their relations with ex situ formation contributed by minor mergers. The flat metallicity and [Mg/Fe] gradients in the thick disc and stellar halo indicate they are dominated by a similar population of ex situ stars. In contrast, the bulge exhibits a negative metallicity gradient ($\nabla[Z/\rm H]_{bulge}
Organisation(s): Department of Astrophysics
Journal: Astronomy & Astrophysics
ISSN: 0004-6361
Publication date: 07-2026
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
Portal url: https://ucrisportal.univie.ac.at/en/publications/d0a4e3e4-7aeb-4547-9c75-b15270878087

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