致密恒星系统中的一个最大恒星表面密度
A Maximum Stellar Surface Density in Dense Stellar Systems
摘要：
我们汇编观测致密恒星系统的表面质量密度分布，包括银河系和附近星系中的球状星团，附近星爆中的大质量星团，矮球状体和晚型盘中的核星团，超致密矮星，以及从低质量尖突凸起和椭圆到大质量核心椭圆的星系球状体。我们发现，在所有情况下，在这些系统的中心区域获得的最大恒星表面密度都是相似的，σ_max ~ 10^11 M_sun/kpc ^2（~20 g/cm ^2），尽管这些系统的恒星总质量M_star跨越7个数量级，有效半径R_e跨越5个数量级，并且有效表面密度M_star/R_e ^2的范围很宽。在不同的系统中，表面密度极限在各种各样的物理尺度上都能达到，因此不是三维恒星密度的极限。考虑到这些不同类别的物体所涉及的非常不同的形成机制，我们认为，一个单一的物理可能决定西格玛_最大。大质量恒星产生的辐射场和风对星团和星系的形成都有重要影响，而超新星和黑洞吸积对恒星团簇形成都不重要。因此，我们得出结论，来自大质量恒星的反馈可能占观测到的Sigma_max，可能是因为恒星形成达到了一个类似爱丁顿的流量，调节这些不同的系统的增长。这表明，目前的星系形成模型，主要集中在超新星和活动星系核的反馈上，缺少一个关键因素。
英文摘要：
We compile observations of the surface mass density profiles of dense stellar systems, including globular clusters in the Milky Way and nearby galaxies, massive star clusters in nearby starbursts, nuclear star clusters in dwarf spheroidals and late-type disks, ultra-compact dwarfs, and galaxy spheroids spanning the range from low-mass cusp bulges and ellipticals to massive core ellipticals. We show that in all cases the maximum stellar surface density attained in the central regions of these systems is similar, Sigma_max ~ 10^11 M_sun/kpc^2 (~20 g/cm^2), despite the fact that the systems span 7 orders of magnitude in total stellar mass M_star, 5 in effective radius R_e, and have a wide range in effective surface density M_star/R_e^2. The surface density limit is reached on a wide variety of physical scales in different systems and is thus not a limit on three-dimensional stellar density. Given the very different formation mechanisms involved in these different classes of objects, we argue that a single piece of physics likely determines Sigma_max. The radiation fields and winds produced by massive stars can have a significant influence on the formation of both star clusters and galaxies, while neither supernovae nor black hole accretion are important in star cluster formation. We thus conclude that feedback from massive stars likely accounts for the observed Sigma_max, plausibly because star formation reaches an Eddington-like flux that regulates the growth of these diverse systems. This suggests that current models of galaxy formation, which focus on feedback from supernovae and active galactic nuclei, are missing a crucial ingredient.
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