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Dissecting the 3D chemo-dynamical structures of NGC~1381: A galaxy hosting an ancient slow bar with an accretion-related bulge and thick disc

  • Yunpeng Jin
  • Ling Zhu
  • Shude Mao
  • Marie Martig
  • Francesca Pinna
  • Glenn van de Ven
  • Yuchen Ding
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Abstract

We applied the barred population-orbit superposition method developed in our 2025 papers 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 fnucl∼5%; (2) a rigidly rotating, BP/X-shaped bar with fbar∼30%; (3) a dynamically hot, spheroidal bulge with fbulge∼17%; (4) a dynamically cold thin disc with fthin∼28%; (5) a vertically extended thick disc with fthick∼16%; and (6) a dynamically hot, spatially diffuse stellar halo with fhalo∼5%. The nuclear disc, bar, and thin disc are metal-rich ([Z/H]≳0), α-poor ([Mg/Fe]≲0.2), and old (∼13 Gyr), corresponding to in situ formation in the early Universe. The bulge, thick disc, and stellar halo are metal-poor ([Z/H]≲0), α-rich ([Mg/Fe]≳0.2), and younger than or comparable in age to the in situ components, suggesting ex situ formation via minor mergers. Further analysis of stellar population gradients reveals that the thick disc and stellar halo, with their flat metallicity and [Mg/Fe] gradients, are likely dominated by a similar ex situ population. In contrast, the bulge exhibits a negative metallicity gradient (∇[Z/H]bulge<0), which might originate from either predominantly ex situ stars or a mixture of in situ and ex situ stars; its ex situ fraction cannot be quantified with the current data. Our modelling also reveals a slow bar (ℛ=2.40−0.27+0.54), with a bar pattern speed of Ωp=34−7+4 km s−1 kpc−1, a bar length of Rbar=2.24−0.22+0.43 kpc, and a corotation radius of RCR=5.38−0.28+1.59 kpc, consistent with its ancient formation time.

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Cite

BibTeXRIS
BibTeX
@misc{jin2026dissecting,
  title = {{Dissecting the 3D chemo-dynamical structures of NGC~1381: A galaxy hosting an ancient slow bar with an accretion-related bulge and thick disc}},
  author = {Yunpeng Jin and Ling Zhu and Shude Mao and Marie Martig and Francesca Pinna and Glenn van de Ven and Yuchen Ding},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2607.00497},
  eprint = {2607.00497},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.00497},
}
RIS
TY  - UNPB
TI  - Dissecting the 3D chemo-dynamical structures of NGC~1381: A galaxy hosting an ancient slow bar with an accretion-related bulge and thick disc
AU  - Yunpeng Jin
AU  - Ling Zhu
AU  - Shude Mao
AU  - Marie Martig
AU  - Francesca Pinna
AU  - Glenn van de Ven
AU  - Yuchen Ding
PY  - 2026
DA  - 2026/10/15
PB  - arXiv
DO  - 10.48550/arxiv.2607.00497
UR  - https://arxiv.org/abs/2607.00497
AB  - We applied the barred population-orbit superposition method developed in our 2025 papers 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_nucl∼5%; (2) a rigidly rotating, BP/X-shaped bar with f_bar∼30%; (3) a dynamically hot, spheroidal bulge with f_bulge∼17%; (4) a dynamically cold thin disc with f_thin∼28%; (5) a vertically extended thick disc with f_thick∼16%; and (6) a dynamically hot, spatially diffuse stellar halo with f_halo∼5%. The nuclear disc, bar, and thin disc are metal-rich ([Z/H]≳0), α-poor ([Mg/Fe]≲0.2), and old (∼13 Gyr), corresponding to in situ formation in the early Universe. The bulge, thick disc, and stellar halo are metal-poor ([Z/H]≲0), α-rich ([Mg/Fe]≳0.2), and younger than or comparable in age to the in situ components, suggesting ex situ formation via minor mergers. Further analysis of stellar population gradients reveals that the thick disc and stellar halo, with their flat metallicity and [Mg/Fe] gradients, are likely dominated by a similar ex situ population. In contrast, the bulge exhibits a negative metallicity gradient (∇[Z/H]_bulge<0), which might originate from either predominantly ex situ stars or a mixture of in situ and ex situ stars; its ex situ fraction cannot be quantified with the current data. Our modelling also reveals a slow bar (ℛ=2.40_−0.27^+0.54), with a bar pattern speed of Ω_p=34_−7^+4 km s^−1 kpc^−1, a bar length of R_bar=2.24_−0.22^+0.43 kpc, and a corotation radius of R_CR=5.38_−0.28^+1.59 kpc, consistent with its ancient formation time.
ER  -