Ongoing hierarchical massive cluster assembly: The LISCA II structure in the Perseus complex
Ongoing hierarchical massive cluster assembly: The LISCA II structure in the Perseus complex
复制标题
正在进行的分层大规模星团组装：英仙座复合体中的 LISCA II 结构
DOI：
10.1051/0004-6361/202346095
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发表时间：
2023
影响因子：
6.5
通讯作者：
Della Croce A
中科院分区：
文献类型：
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作者：
Della Croce A
我们报告了在银河系英仙座复合体中发现的一个巨大的（∼105M⊙）亚结构恒星系统，可能正在进行分级星团组装。该系统由九个星团（包括众所周知的星团 NGC 654 和 NGC 663）和一个扩展的低密度恒星晕组成。Gaia-DR3 和可用的光谱数据表明，其所有组成部分在 6D 相空间（位置、视差和 3D 运动）中物理上一致，并且年龄（14-44 Myr）和化学含量（半太阳）均质。 金属度）。此外，该系统的全球恒星密度分布是典型星团的分布，并显示出明显的质量偏聚证据。我们发现，层次结构主要以高达 ≃4 − 5 km s−1 的速度向中心收缩，而最内部区域以较低的速率（约 ≃1 km s−1）扩张，并且以随机运动为主。有趣的是，这种模式主要由大质量恒星的运动学主导，而低质量恒星（M< 2M⊙）的特征是整个星团的收缩。最后，系统中的九个星团都具有相对平坦的速度分散剖面，这可能是由持续的相互作用和潮汐加热造成的。我们表明，观测结果与星团剧烈弛豫阶段后的 N 体模拟结果基本一致，强烈表明该系统在早期组装阶段是一个巨大的星团。这是我们银河系中第二个具有这些特性的结构，根据我们之前工作的命名法，我们将其命名为 LISCA II。
We report on the identification of a massive (∼105M⊙) substructured stellar system in the Galactic Perseus complex likely undergoing hierarchical cluster assembly. This system comprises nine star clusters (including the well-known clusters NGC 654 and NGC 663) and an extended and low-density stellar halo.Gaia-DR3 and available spectroscopic data show that all its components are physically consistent in 6D phase-space (position, parallax, and 3D motion), and homogeneous in age (14–44 Myr) and chemical content (half-solar metallicity). In addition, the system’s global stellar density distribution is that of typical star clusters and shows clear evidence of mass segregation. We find that the hierarchical structure is mostly contracting toward the center with a speed of up to ≃4 − 5 km s−1, while the innermost regions expand at a lower rate (about ≃1 km s−1) and are dominated by random motions. Interestingly, this pattern is dominated by the kinematics of massive stars, while low-mass stars (M< 2M⊙) are characterized by contraction across the entire cluster. Finally, the nine star clusters in the system are all characterized by a relatively flat velocity dispersion profile possibly resulting from ongoing interactions and tidal heating. We show that the observational results are generally consistent with those found inN-body simulations following the cluster violent relaxation phase, strongly suggesting that the system is a massive cluster in the early assembly stages. This is the second structure with these properties identified in our Galaxy and, following the nomenclature of our previous work, we named it LISCA II.