Probing Hydrogen and Helium Reionization

Oh博士和他的团队将研究新形成的星系对弥散星系间介质的影响，因为来自年轻恒星和活跃原子核的紫外线辐射会使气体再电离。他们将把蒙特卡罗辐射转移纳入合作者吉田的宇宙流体动力学代码中，并使用该代码研究辐射压力和Lyman-alpha光子的捕获如何调节早期原始星系中的恒星形成和气体流动。几个正在建造的低频射电望远镜将测量宇宙大爆炸后不到5亿年中性氢气发出的21厘米红移辐射。Oh博士和他的团队将开发更好的数值算法和统计数据来分析这些观测结果，并从附近的物体中去除信号。这将更好地测量中性气体的比例如何随时间减少，以及新生星系电离区域的位置和大小。剩余的中性气体在遥远类星体的光谱中产生吸收线。这个团队将通过模拟得出一个改进的模型，以便更好地估计氢和氦再电离的时间，早期星系间气体的状态方程，以及接近今天的星系间气体云集群。研究生和本科生都将通过参与研究得到训练。Oh博士和他的团队将把他们的分析代码提供给天文学界。这是一个与日本研究者合作的国际项目。

Dr Oh and his team will study the effect of newly-forming galaxies on the diffuse intergalactic medium, as the ultraviolet radiation from their young stars and active nuclei reionizes the gas. They will incorporate Monte-Carlo radiative transfer into the cosmological hydrodynamics code of collaborator Yoshida, and use this code to investigate how radiation pressure and the trapping of Lyman-alpha photons can regulate star formation and gas flow in early proto-galaxies. Several low-frequency radio telescopes now under construction will measure the redshifted 21cm radiation emitted by neutral hydrogen gas less than half a billion years after the Big Bang. Dr Oh and his team will develop better numerical algorithms and statistics to analyze these observations, and to remove signals from nearby objects. This will provide better measures of how the fraction of neutral gas decreases with time, and of the location and size of the regions ionized by nascent galaxies. The remaining neutral gas produces absorption lines in the spectra of distant quasars. This team will use simulations to derive an improved model that will allow better estimates for the time that hydrogen and helium were reionized, for the equation of state of the intergalactic gas at early times, and for the clustering of intergalactic gas clouds close to the present day.Both graduate and undergraduate students will be trained by participating in the research. Dr Oh and his team will make their analysis codes available to the astronomical community. This is an international project in collaboration with a Japanese investigator.