Regulating star formation in diverse galactic environments

在我们的银河系和其他星系中，恒星形成于密集的氢分子云中。星系如何随时间形成和演化与恒星形成的过程密切相关。然而，更大尺度环境对星系分子气体含量的影响却知之甚少。我将测量附近螺旋星系样本中的分子气体含量和性质，探测从孤立星系到星系群再到巨大的室女座星系团的环境。一种可能性是，与邻近星系的引力相互作用是导致原子氢气通过径向流入转化为分子氢气的原因。这项独特的工作将确定环境在塑造星系分子气体含量方面的作用，并将这项工作置于星系恒星形成和星系演化模型的背景下。**两个星系的剧烈合并在本地宇宙中产生了一些最极端的恒星形成环境，恒星形成的速度比正常星系快10到100倍。我将测量分子气体的物理和动力学特性在合并过程中是如何变化的，以查明星系合并中恒星形成速度增加的机制，以及气体消耗速度的类似增加。我还将测量分子气体中的冷却速率，并使用辐射传输模型来约束气体的热源，如紫外线光子、x射线光子或冲击。我的工作将为星系合并的数值模型以及早期宇宙中星系形成的模型提供输入物理的关键测试。**当今天体物理学最重要的问题之一是理解是什么决定了恒星诞生时的质量分布。我将对银河系分子云中致密核的特性进行详细研究，以补充我在河外恒星形成方面的工作。这些密集的核心被认为是单个恒星形成的地方。我将测量岩心质量的分布，并确定岩心的性质是否随当地环境而变化，从孤立的岩心到沿着细丝的岩心，再到小的岩心簇。我还将确定细丝是否为致密核的形成提供了必要的环境。我的工作将测试我们对致密核心与恒星诞生时质量分布之间关系的理解的稳健性。

In our own Milky Way and in other galaxies, stars form inside dense clouds of molecular hydrogen gas. How galaxies form and evolve with time is intimately tied to this process of star formation. However, the effect of the larger scale environment on the molecular gas content of galaxies is poorly understood. I will measure the molecular gas content and properties in a sample of nearby spiral galaxies probing environments from isolated galaxies to galaxy groups to the massive Virgo cluster of galaxies. One possibility is that gravitational interactions with neighbouring galaxies are responsible for driving the conversion of atomic hydrogen gas to molecular hydrogen gas through radial inflows. This unique work will determine the role of environment in shaping the molecular gas content of galaxies and place this work in the context of models of galactic star formation and galaxy evolution. **The violent mergers of two galaxies produce some of the most extreme star formation environments in the local universe, with stars forming at a rate that is ten to one hundred times faster than in normal galaxies. I will measure how the physical and dynamical properties of the molecular gas change during the merger process to pinpoint the mechanisms responsible for the increase in the rate of star formation in galaxy mergers as well as the similar increase in the rate of gas consumption. I will also measure the rate of cooling in the molecular gas and use radiative transfer models to constrain the heating sources for the gas, such as ultraviolet photons, X-ray photons, or shocks. My work will provide a critical test of the input physics to numerical models of galaxy mergers, as well as models of galaxy formation in the early universe. **One of the most important issues in astrophysics today is understanding what sets the distribution of masses with which stars are born. I will complement my work on extragalactic star formation with a detailed study of the properties of dense cores in molecular clouds in our own Milky Way. These dense cores are known to be the sites where individual stars are formed. I will measure the distribution of masses of the cores and determine whether the properties of the cores change with the local environment, from isolated cores to cores along filaments to small clusters of cores. I will also determine whether filaments provide the necessary environment for the formation of dense cores. My work will test the robustness of our understanding of the relationship between the dense cores and the distribution of masses with which stars are born.