Reionization, Environment, and the Galaxy Content of Milky-Way Mass Halos

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。Wechsler博士和她的团队将探索氢气如何被最早的恒星和活动星系核的紫外线辐射重新电离，以及如何影响小星系中的星星形成。 标准的冷暗物质宇宙学预测了更多的低质量暗晕，聚集在更大的暗晕周围，而不是我们观察到的更大星系的卫星。 但来自较大星系的紫外线辐射可能会阻止最小卫星暗晕中的气体坍缩形成恒星，因此那里没有星系诞生。 韦克斯勒博士的工作将改进目前的研究，这些研究假设整个宇宙在同一时间重新电离。 她和她的团队将首先运行仅包括暗物质的大型宇宙学N体模拟。 然后，他们将研究紫外线辐射水平的变化如何改变可能容纳微弱卫星星系的下沉subhalos的数量。 然后，该团队将使用大规模模拟，以及再电离模型，来估计像我们银河系这样的星系周围可能的紫外线辐射水平的范围。 计算将预测斑块再电离如何影响银河系大小的星系的预期卫星人口，并研究星系的再电离历史与其卫星人口，形成过程和环境之间存在什么关系。一名西班牙裔博士后和一名研究生将在参与研究时接受培训。 韦克斯勒博士所在机构的一个项目中，来自代表性不足群体的学生也将参与其中。 她将继续参加公共宣传讲座和为高中编写课程材料。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Wechsler and her team will explore how hydrogen gas is re-ionized by the ultraviolet radiation from the earliest stars and active galactic nuclei, and how that affects star formation in small galaxies. The standard Cold Dark Matter cosmologies predict many more low-mass dark halos, clumped around much larger dark halos, than we observe as satellites of larger galaxies. But ultraviolet radiation from the larger galaxy may prevent gas in the smallest satellite dark halos from collapsing to form stars, so that no galaxy is born there. Dr. Wechsler's work will improve on current studies, which assume that the entire cosmos reionizes at a single time. She and her team would first run large cosmological N-body simulations including only the dark matter. They will then examine how changing the level of ultraviolet radiation alters the number of infalling subhalos that could host faint satellite galaxies. The team will then use the large-scale simulations, together with models for reionization, to estimate the range of possible ultraviolet radiation levels around a galaxy like our Milky Way. The calculations will predict how patchy reionization affects the expected satellite population of Milky-Way-sized galaxies, and examine what relations exist between a galaxy's reionization history and its satellite population, formation process, and environment.A Hispanic postdoc and a graduate student will be trained as they participate in the research. Students from under-represented groups in a program at Dr. Wechsler's institution will also be involved. She will continue to participate in public outreach lectures and in developing curriculum material for high schools.