arXiv 2303.016372023-03astro-ph.GA

银河系球状星团的多质量建模——I. 对1 M$_{\odot}$以上恒星初始质量函数的启示

Multimass modelling of Milky Way globular clusters -- I. Implications on their stellar initial mass function above 1 M$_{\odot}$

Nolan Dickson, Vincent Hénault-Brunet, Holger Baumgardt, Mark Gieles, Peter Smith

备注：: 21 pages, 10 figures, MNRAS accepted
DOI：: 10.1093/mnras/stad1254

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AI总结：

本研究通过多质量模型分析37个银河系球状星团的多源观测数据，发现1倍太阳质量以上的高质量端恒星初始质量函数符合Salpeter形式，与顶重IMF假说不符，且该斜率与星团金属丰度无显著关联。

摘要：

球状星团内恒星与恒星遗迹（白矮星、中子星、黑洞）的分布蕴藏着其形成与长期演化的线索，对研究星团的初始质量函数（IMF）及黑洞并合的形成具有重要意义。本研究中，我们给出了37个银河系球状星团的最佳拟合多质量模型，这些模型由多类数据集推导得出，包括Gaia EDR3和哈勃空间望远镜（HST）的自行数据、地基光谱观测的视向速度数据，以及HST的深场恒星质量函数数据。我们采用与金属丰度相关的恒星演化配方，从初始质量函数推导得到恒星与遗迹的现今质量函数。通过动力学探测星团内所有天体的现今质量函数（包括遗迹的质量分布），这些模型使我们能够详细探究大样本银河系球状星团（GCs）的恒星（初始）质量函数。研究表明，尽管低质量端的质量函数斜率强烈依赖于星团的动力学年龄，但高质量端斜率（$α_3$；质量$m > 1 M_\odot$）并非如此，说明该质量区间的质量函数通常受动力学质量损失的影响较小。对该高质量端质量函数斜率的分析显示，此质量区间的IMF需与Salpeter IMF（萨尔彼得初始质量函数）一致才能重现观测结果。该高质量端IMF与近期提出的顶重IMF（top-heavy IMF）并不相符。最后，基于对银河系球状星团样本的多质量模型拟合，我们未发现高质量端IMF斜率与星团金属丰度之间存在显著相关性。

英文摘要：

The distribution of stars and stellar remnants (white dwarfs, neutron stars, black holes) within globular clusters holds clues about their formation and long-term evolution, with important implications for their initial mass function (IMF) and the formation of black hole mergers. In this work, we present best-fitting multimass models for 37 Milky Way globular clusters, which were inferred from various datasets, including proper motions from Gaia EDR3 and HST, line-of-sight velocities from ground-based spectroscopy and deep stellar mass functions from HST. We use metallicity dependent stellar evolution recipes to obtain present-day mass functions of stars and remnants from the IMF. By dynamically probing the present-day mass function of all objects in a cluster, including the mass distribution of remnants, these models allow us to explore in detail the stellar (initial) mass functions of a large sample of Milky Way GCs. We show that, while the low-mass mass function slopes are strongly dependent on the dynamical age of the clusters, the high-mass slope ($α_3; m > 1 M_\odot$) is not, indicating that the mass function in this regime has generally been less affected by dynamical mass loss. Examination of this high-mass mass function slope suggests an IMF in this mass regime consistent with a Salpeter IMF is required to reproduce the observations. This high-mass IMF is incompatible with a top-heavy IMF, as has been proposed recently. Finally, based on multimass model fits to our sample of Milky Way GCs, no significant correlation is found between the high-mass IMF slope and cluster metallicity.

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