Probing Hydrogen and Helium Reionization

Oh博士和他的团队将研究新形成的星系对弥漫的星系际介质的影响，因为来自年轻恒星和活动核的紫外线辐射使气体重新电离。 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，并使用该代码来研究辐射压力和莱曼α光子的捕获如何调节早期原星系中的星星形成和气体流动。 目前正在建造的几个低频射电望远镜将测量大爆炸后不到5亿年中性氢气发出的红移21厘米辐射。 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，并消除附近物体的信号。 这将提供更好的测量中性气体的比例如何随着时间的推移而减少，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的类星体的光谱中产生吸收线。 该团队将使用模拟来导出一个改进的模型，该模型将允许更好地估计氢和氦被再电离的时间，早期星系际气体的状态方程，以及接近今天的星系际气体云的聚集。研究生和本科生都将通过参与研究进行培训。 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人员合作的国际项目。

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.