Search for dark baryon in the universe using oxygen emission lines in soft X-ray band

1)我们和我们的德国合作者Klaus Dolag博士一起开发并运行了一个宇宙水密码。该代码考虑了各种物理过程，包括辐射冷却、恒星形成、超新星引起的气体加热、化学演化。2)利用上述模拟结果，我们在局部宇宙中构建了模拟星系目录，并讨论了通过氧发射线探测邻近星系团外围相关的WHIM （warm-hot intergalactic medium）的可行性（Yoshikawa et al. 2004）。3)我们还研究了利用背景类星体和伽玛射线爆发后的x射线探测WHIM吸收谱线的可行性（Kawahara et al. 2006）。4)指出了WHIM中的元素丰度不服从电离平衡。我们利用模拟数据跟踪了氧电离态的时间演化，确实证明了在WHIM中电离平衡是不成立的。我们发现，不同电离状态下氧谱线的强度比是偏离电离平衡的一个很好的指标（Yoshikawa和Sasaki 2006）。5)提出了一种新的星系团内介质温度和密度不均匀性的经验分析模型，并证明该模型很好地解释了钱德拉x射线卫星对A3667星系团的观测数据（kawahar et al.2007,2008）。

1) We developed and ran a cosmological hydro-code with our German collaborator, Dr. Klaus Dolag. The code takes account of a variety of physical processes including radiative cooling, star formation, gas heating due to supernovae, chemical evolution.2) Using the above simulation results, we constructed a mock galaxy catalog in the Local Universe, and discussed the detection feasibility of WHIM (warm-hot intergalactic medium) associated with outskirts of nearby galaxy clusters via oxygen emission lines (Yoshikawa et al. 2004).3) We also studied the detection feasibility of absorption lines of WHIM using the background quasars and X-ray after glow of gamma-ray bursts (Kawahara et al. 2006).4) It has been pointed out that the element abundance in WHIM does not obey the ionization equilibrium. We followed the time evolution of the oxygen ionization states using the simulation data, and indeed showed that the ionization equilibrium is not valid in WHIM. We found that the intensity ratio of oxygen lines in different ionization states is a good indicator of the departure from the ionization equilibrium (Yoshikawa and Sasaki 2006).5) We proposed a new empirical analytic model for temperature and density inhomogeneities in intra-cluster medium, and showed that this nice explains the observation data of galaxy cluster A3667 from Chandra X-ray satellite (kawahar et al.2007,2008).