Probing Hydrogen and Helium Reionization

吴博士和他的团队将研究新形成的星系对弥漫星际介质的影响，因为来自年轻恒星和活动核的紫外线辐射会使气体重新电离。他们将把蒙特卡罗辐射传输纳入合作者吉田的宇宙流体力学程序中，并使用这个程序来研究辐射压力和莱曼-阿尔法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。几个正在建设中的低频射电望远镜将测量宇宙大爆炸后不到5亿年的中性氢气发出的红移21厘米的辐射。吴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，并删除附近天体的信号。这将更好地测量中性气体的比例如何随时间减少，以及被新生星系电离的区域的位置和大小。剩下的中性气体在遥远类星体的光谱中产生了吸收谱线。这个团队将使用模拟来得出一个改进的模型，该模型将允许更好地估计氢和氦重新电离的时间，早期星系间气体的状态方程，以及接近现在的星系间气体云的聚集。研究生和本科生都将通过参与这项研究进行培训。吴博士和他的团队将向天文学社区提供他们的分析代码。这是一个与日本调查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.