Probing Galaxy-Formation Physics: A Bayesian Inference Approach

星系形成和演化的半解析模型(SAM)使用相对简单但物理驱动的参数化处方来描述复杂过程的影响，如合并、气体吸积、恒星形成和反馈，以跟踪整个宇宙时间的模拟星系群。虽然不准确，但SAM是必要的，因为对这些过程的直接模拟仍然超出了计算硬件和技术的能力范围。SAMS的缺点是可调参数之间的简并度可能很大，而且很难理解。对此，提出建议的团队开发了基于贝叶斯推理的SAM。贝叶斯方法给出了给定数据集的SAM参数的后验概率分布，并评估了数据对特定模型的支持程度。在这个项目中，该团队将把他们的分析应用于高红移星系的档案数据，并解决以下问题：(1)星系如何聚集它们的质量，不同星系中的恒星形成如何进行，以及普遍的恒星初始质量函数是否与数据一致；(2)反馈如何影响星系中的气体成分，以及为什么今天大多数重子不在星系中；(3)超大质量黑洞的增长，以及来自活动星系核(AGN)的反馈如何影响星系的形成和演化；(4)高红移电离源的性质和宇宙是如何重新电离的；(5)冷暗物质(CDM)范式是否能适应星系的所有观测性质。这些模型将被用来创建针对特定星系调查的属性量身定做的模拟星系星表；该团队将向社区提供这些模拟星表。该项目将支持研究生的工作和专业培训，并旨在为本科生提供研究机会。

Semi-analytic models of galaxy formation and evolution (SAMs) use relatively simple, but physically motivated parameterized prescriptions for the effects of complex processes such as merging, gas accretion, star formation, and feedback to follow a simulated population of galaxies through cosmic time. Though inexact, SAMs are necessary since direct simulation of these processes is still beyond the reach of computational hardware and techniques. The disadvantage of SAMs is that the degeneracies among the adjustable parameters can be large and poorly understood. In response, the proposing team has developed a Bayesian inference based SAM. The Bayesian approach yields the posterior probability distribution of the SAM parameters for a given set of data, and an assessment of how well a particular model is supported by the data. In this project, the team will apply their analysis to archival data on high-redshift galaxies, and address the following issues: (1) how galaxies assemble their masses, how star formation proceeds in different galaxies, and whether a universal stellar initial mass function is consistent with the data; (2) how feedback affects the gas component in galaxies, and why most of the baryons today are not in galaxies; (3) the growth of supermassive black holes, and how feedback from active galactic nuclei (AGN) affects galaxy formation and evolution; (4) the properties of ionizing sources at high redshift and how the Universe was re-ionized; (5) whether the Cold Dark Matter (CDM) paradigm can accommodate all observational properties of galaxies. These models will be used to create mock galaxy catalogs tailored to the properties of specific galaxy surveys; the team will make these mock catalogs available to the community. The project will support the work and professional training of a graduate student, and is intended to provide research opportunities for undergraduates.