Stellar initial mass function varies with metallicity and time
Stellar initial mass function varies with metallicity and time
复制标题
恒星初始质量函数随金属丰度和时间而变化
DOI：
10.1038/s41586-022-05488-1
复制
发表时间：
2023
期刊：
影响因子：
64.8
通讯作者：
Yan Zhi-Qiang
中科院分区：
文献类型：
--
作者：
Li Jiadong;Liu Chao;Zhang Zhi-Yu;Tian Hao;Fu Xiaoting;Li Jiao;Yan Zhi-Qiang
星系的大多数结构和演化特性强烈依赖于恒星初始质量函数（IMF），即在恒星形成的每个阶段形成的恒星质量的分布， , – 。 IMF 塑造了所有恒星系统中的恒星种群，因此已成为现代天文学最基本的概念之一。尽管进行了大量的理论和观测工作，但不同环境下的恒定国际货币基金组织和可变国际货币基金组织已被声称。然而，银河系恒星群中 IMF 的测量受到光度观测恒星数量相对较少的限制，导致高度不确定性 , , , – 。在这里，我们报告了基于大约 93,000 颗光谱观测到的 M 矮星的恒星计数结果，比之前的研究多了一个数量级，位于 100-300 秒差距的太阳附近。我们发现了变量 IMF 的明确证据，该变量取决于金属丰度和恒星年龄。具体来说，与标准 IMF 相比，早期形成的恒星群包含较少的低质量恒星，与恒星金属丰度无关。然而，在最近的时期，低质量恒星的比例随着恒星金属丰度的增加而增加。银河系中低质量恒星的丰度变化为恒星形成模型建立了强大的基准，并且可以严重影响银河系化学富集建模、星系质量估计和行星形成效率的结果。
Most structural and evolutionary properties of galaxies strongly rely on the stellar initial mass function (IMF), namely the distribution of the stellar mass formed in each episode of star formation, , –. The IMF shapes the stellar population in all stellar systems, and so has become one of the most fundamental concepts of modern astronomy. Both constant and variable IMFs across different environments have been claimed despite a large number of theoretical, –and observational efforts, , , , , , –. However, the measurement of the IMF in Galactic stellar populations has been limited by the relatively small number of photometrically observed stars, leading to high uncertainties, , , –. Here we report a star-counting result based on approximately 93,000 spectroscopically observed M-dwarf stars, an order of magnitude more than previous studies, in the 100–300 parsec solar neighbourhood. We find unambiguous evidence of a variable IMF that depends on both metallicity and stellar age. Specifically, the stellar population formed at early times contains fewer low-mass stars compared with the canonical IMF, independent of stellar metallicities. In more recent times, however, the proportion of low-mass stars increases with stellar metallicity. The variable abundance of low-mass stars in our Milky Way establishes a powerful benchmark for models of star formation and can heavily affect results in Galactic chemical-enrichment modelling, mass estimation of galaxies and planet-formation efficiency.