发表机构
Pontificia Universidad Católica de Chile; Instituto de Astrofísica, Pontificia Universidad Católica de Chile; Centro de AstroIngeniería, Pontificia Universidad Católica de Chile; Instituto de Astronomía y Física del Espacio, CONICET-UBA（智利天主教 Pontificia 大学; 智利天主教 Pontificia 大学天体物理研究所; 智利天主教 Pontificia 大学天文工程中心; 空间天文与物理研究所，阿根廷国家科学研究委员会-布宜诺斯艾利斯大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用CIELO模拟识别出星系核球中心的恒星结，发现它们富α元素、形成更早更快，多为原位形成，可能是早期核球组装的化石遗迹。
AI 中文摘要
在宇宙化学流体动力学放大模拟套件CIELO的一部分星系中，发现了位于核球中心、尺度约1千秒差距的深束缚恒星亚结构。这些结构是通过每个星系圆度-能量$(\epsilon, E)$平面上最低束缚能处的恒星过密度识别出来的。我们将这些过密度称为恒星结。我们旨在利用CIELO模拟星系（其恒星质量范围广泛，为$10^{8.0}$至$10^{10.7}\\,\mathrm{M}_{\odot}$，且形成历史多样）来表征它们在核球组装背景下的性质。我们检查了54个星系核球。在其中，我们在$(\epsilon, E)$空间中分离出恒星结候选体，并识别出28个满足连续选择标准（运动学、浓度和形态）的稳健恒星结。我们表征了它们的化学增丰、形成时标、形成位置、前身气体来源和空间分布。在所有星系质量中，恒星结系统性地富集α元素，其恒星质量的主体形成于更早的时期且时标更短（中位数约2吉年，而其他核球族群约为5吉年），与其他核球族群相比。关于其起源，恒星结主要是在原位形成的（吸积质量分数为5%，约为核球其余部分的一半），盘生恒星贡献可忽略不计，且最大气体分数来自原始中心球体（21%，而周围族群为16%至17%），这与作为α元素增丰的主要气体燃料一致。在结构方面，恒星结表现出多种形态，以球状形状为主。在CIELO星系的$(\epsilon, E)$空间中进行动力学选择证明了其在恢复同年龄恒星族群方面的有效性，表明恒星结可能是早期原位核球组装的化石遗迹。
英文摘要
Deeply bound stellar substructures of about 1 kpc at the center of bulges are found in a subset of galaxies from the cosmological chemo-hydrodynamical zoom-in CIELO simulation suite. They were identified as stellar overdensities at the lowest binding energies in each galaxy's circularity-energy $(ε, E)$ plane. We refer to these overdensities as stellar knots. We aim to characterize their properties in the context of bulge assembly using CIELO simulated galaxies spanning a wide range of stellar masses ($10^{8.0}$-$10^{10.7}\,\mathrm{M}_{\odot}$), with diverse formation histories. We inspect 54 galactic bulges. Within them, we isolate stellar knot candidates in $(ε, E)$ space, and identify 28 robust knots satisfying successive selection criteria: kinematic, concentration, and morphology. We characterize their chemical enrichment, formation timescales, formation sites, progenitor gas origin, and spatial distributions. Across all galaxy masses, knots are systematically alpha-element enhanced, having assembled the bulk of their stellar mass at earlier epochs and on shorter timescales than other bulge populations, with a median of $\sim$2$\,$Gyr versus $\sim$5$\,$Gyr. Regarding their origin, knots are predominantly in-situ ($5\%$ accreted mass fraction, roughly half that of the rest of the bulge), with negligible disk-born stars contribution and the largest gas fractions originating from a primordial central spheroid ($21\%$ versus 16--17$\%$ for the surrounding populations), consistent with being the primary gas fuel for the alpha-element enhancement. In terms of structure, knots exhibit a variety of morphologies, with spheroidal shapes predominating. Dynamical selection in $(ε, E)$ space of CIELO galaxies demonstrates its effectiveness in recovering coeval stellar populations, pointing to stellar knots as plausible fossil signatures of early in-situ bulge assembly.
CommentsAccepted for publication in Astronomy & Astrophysics
