AI 中文总结
本文提出Gal3D框架，通过超椭球拟合量化IllustrisTNG与EAGLE模拟星系的径向三维结构，揭示不同质量星系的形态差异及模拟间的形态特征区别，为对比宇宙学模拟的星系形态提供实用工具。
AI 中文摘要
星系的形态与结构是星系形成和演化的关键示踪体，因此准确测量星系的本征三维形状，对关联形态与星系并合过程、开展数值模拟对比研究至关重要。本文提出Gal3D框架，该框架可从粒子数据中重建平滑密度场，并通过将超椭球拟合到等密度面，量化模拟星系的径向三维结构。该方法可获取轴比、取向、中心偏移量及超椭球指数（$S_a$、$S_b$、$S_c$），能灵活表征盘、经典核球、箱形/花生形核球、三轴分量等多种星系结构。将Gal3D应用于IllustrisTNG与EAGLE模拟中的星系，研究发现：扁平盘区的径向范围随恒星质量$M_{*,30}$增大，在$M_{*,30}\backsim10^{11}\\,M_\odot$时达到峰值后急剧下降，其中EAGLE星系在$M_{*,30}\backsim10^{10.5}\\,M_\odot$时出现饱和；两个模拟中，与棒相关的参量$\varepsilon_{ab}\equiv1-b/a$在$M_{*,30}\backsim10^{10.5}\\,M_\odot$以上时均增强，但EAGLE星系的该参量系统性更弱；TNG星系的外棒区域通常伴随$S_a$与$S_c$升高，表明其箱形特征增强、箱形/花生形核球更显著，而EAGLE星系的此类高阶特征较弱或不存在；在最高恒星质量端，扁平盘的显著性降低，内部长椭球或三轴结构仍普遍存在，且大质量EAGLE星系的外部恒星天体比TNG对应星系更偏向长椭球或三轴结构。这些结果表明，Gal3D为量化本征径向三维结构、对比宇宙学模拟间的形态差异提供了实用框架。
英文摘要
Galaxy morphology and structure are key tracers of galaxy formation and evolution, making accurate measurements of intrinsic three-dimensional (3D) shape essential for linking morphology to galaxy assembly and for comparing numerical simulations. We present Gal3D, a framework that reconstructs smoothed density fields from particle data and quantifies the radial 3D structure of simulated galaxies by fitting superellipsoids to iso-density surfaces. The method recovers axis ratios, orientations, center offsets, and superellipsoid indices ($S_a$, $S_b$, $S_c$), enabling a flexible characterization of diverse galactic structures such as disks, classical bulges, box/peanut bulges, and triaxial components. Applying Gal3D to galaxies in the IllustrisTNG and EAGLE simulations, we find that the radial extent of flattened disk regions increases with stellar mass up to $M_{*,30}\sim10^{11}\,M_\odot$ and then declines sharply, with EAGLE galaxies showing a saturation at $M_{*,30}\sim10^{10.5}\,M_\odot$. The bar-related $ \varepsilon_{ab}\equiv 1-b/a$ strengthens above $M_{*,30}\sim10^{10.5}\,M_\odot$ in both simulations, but remains systematically weaker in EAGLE. In TNG, outer bar regions are commonly associated with elevated $S_a$ and $S_c$, indicating enhanced boxiness and more prominent box/peanut-shaped bulges, whereas such higher-order signatures are weak or absent in EAGLE. At the highest stellar masses, flattened disks become less prominent, while inner prolate or triaxial structures remain common and massive EAGLE galaxies have more prolate or triaxial outer stellar bodies than their TNG counterparts. These results demonstrate that Gal3D provides a practical framework for quantifying intrinsic radial 3D structure and comparing morphology across cosmological simulations.
Comments22 pages, 11 figures. Accepted for publication in ApJ. Source code: https://github.com/GalaxySimAnalytics/gal3d, and data: https://osf.io/k9x3e/
