解码恒星形成主序列或：我如何学会停止担心并爱上中心极限定理
Decoding the Star-Forming Main Sequence or: How I Learned to Stop Worrying and Love the Central Limit Theorem
摘要：
盘状星系的恒星形成率（SFR）与恒星质量密切相关，在固定质量时，SSFR的离散度很小，σ ~ 0.3dex。由于这种小的分散，恒星形成主序列（SFMS）被解释为确定性和基本的。这里我们证明它是中心极限定理的一个简单推论。我们的推导开始近似原位恒星质量增长作为一个随机过程，很像一个随机行走（在任何时候的期望SFR等于SFR在前一个时间）。然后，我们得出期望值的中位数SSFR的恒星形成磁盘和他们的分散随着时间的推移。我们推广的随机变化的SFR，不是相互独立的，但随着时间的推移相关的结果。对于无偏样本（盘）星系，我们得到的期望，<SSFR>应该是独立的质量，下降为1/T，并有一个相对的分散，是独立的质量和时间。导出的SFMS及其演变与已发表的数据相匹配，z=10，具有足够的精度来约束宇宙学参数。该框架再现了几个重要的可观测量，包括：在固定质量的SSFR的散射;附近矮星系和银河系的SFH;和塔利-费舍尔关系的散射。质量函数的演变是不太好再现，我们讨论的方法来概括的框架，包括其他来源的恒星质量，如合并。在SSFR中预测的色散对静止星系的分类有影响，因为这样的星系有异质的形成历史，许多可能只是暂时减少了它们的恒星形成活动。SFH中隐含的分散性，以及SFMS对随机性时间尺度的不敏感性，因此大大限制了在长宇宙基线上连接大质量星系与其祖先的能力。[TRUCH.]
英文摘要：
Star-formation rates (SFR) of disk galaxies strongly correlate with stellar mass, with a small dispersion in SSFR at fixed mass, sigma~0.3 dex. With such small scatter this star-formation main sequence (SFMS) has been interpreted as deterministic and fundamental. Here we demonstrate that it is a simple consequence of the central limit theorem. Our derivation begins by approximating in situ stellar mass growth as a stochastic process, much like a random walk (where the expectation of SFR at any time is equal to the SFR at the previous time). We then derive expectation values for median SSFR of star-forming disks and their scatter over time. We generalize the results for stochastic changes in SFR that are not independent of each other but are correlated over time. For unbiased samples of (disk) galaxies, we derive an expectation that <SSFR> should be independent of mass, decline as 1/T, and have a relative scatter that is independent of mass and time. The derived SFMS and its evolution matches published data to z=10 with sufficient accuracy to constrain cosmological parameters. The framework reproduces several important observables, including: the scatter in SSFR at fixed mass; the SFHs of nearby dwarf galaxies and the Milky Way; and the scatter in the Tully-Fisher relation. The evolution of the mass function is less well reproduced and we discuss ways to generalize the framework to include other sources of stellar mass such as mergers. The predicted dispersion in SSFR has consequences for the classification of quiescent galaxies, as such galaxies have heterogeneous formation histories, and many may only be temporarily diminished in their star-formation activity. The implied dispersion in SFHs, and the SFMS's insensitivity to timescales of stochasticity, thus substantially limits the ability to connect massive galaxies to their progenitors over long cosmic baselines. [TRUNC.]
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