The Study of QSO Absorption Lines using 3D Radiative Transfer

最近，人们认为类星体光谱中的LYA吸收系统可以用星际过密集涨落的吸收来解释。然而，以前的所有工作都是基于光学厚度或局部光学深度近似。在这里，我们给出了宇宙电离和类星体吸收线系统形成的三维辐射传输计算，宇宙中所产生的电离度在不同的地方相差三个数量级以上。由于这种不均匀的电离结构，相对较低的电离区在类星体光谱中会产生较强的吸收。为了与观测结果进行直接比较，我们模拟了吸收线。首先，我们关注LYA吸收。事实证明，所谓的Gunn-Peterson效应就是在进行低色散光谱时，吸收线的重叠效应。为了将模拟结果与观察值…进行定量比较此外，我们还对连续谱抑制D_A进行了评估，发现任何具有恒定UV强度的模型都不符合D_A在高红移达5的情况下快速增长的观测趋势。这意味着元银河系的UV强度必须在z&gt；5处随z迅速减小至少两个数量级。如果z=5的UV强度在较高的红移时保持不变，则再电离周期估计为z&lt；reion&gt；&gt；7-然而，Lya吸收不适合于更准确地确定再电离周期，因为即使平均中性分数小于10^&lt；-2&gt；，Lyα也过于强烈地亏损。因此，为了研究z&gt；处的宇宙，一条线需要三个条件；5：(1)线发射是可探测的，(2)它的线不透明度比LYA低，(3)它对尘埃的消光较低，因为年轻的恒星形成星系经常被尘埃覆盖。最有利的溶液是Ha吸收线。事实上，我们已经发现，Ha连续谱凹陷更准确地追踪了再电离历史。哈林的波长在3μm[小于或相似]λ_&lt；Hα&gt；[小于或相似]7μm处下降到4[小于或相似]z[小于或相似]10。因此，可以用斯巴鲁红外光谱仪进行观测。较少

Recently, it has been considered that the Lya absorption systems in QSO spectra can be accounted for in terms of the absorption by intergalactic overdense fluctuations. However, all of previous works have been based upon optically-thin or local optical-depth approximations. Here, we present 3D radiative transfer calculations on the cosmic reionization and the formation of QSO absorption line systems.The resultant ionization degrees in the universe are different from place to place by more than three orders of magnitude. Due to such inhomogeneous ionization structure, relatively low ionization regions could produce strong absorption in QSO spectra. To make a direct comparison with the observations, we have simulated absorption lines. First, we focus on Lya absorption. It has turned out that the so-called Gunn-Peterson effect appears as the overlapping effect of absorption lines just when low dispersion spectroscopy is made. In order to compare the simulations quantitatively with observa … More tions, we have assessed the continuum depression, D_A. It is found that any model with a constant UV intensity does not match the observed trend that D_A tends to grow quickly at higher redshifts up to 5. This implies that the metagalactic UV intensity must decrease rapidly with z at z > 5 by two orders of magnitude at least. If the well fitted value of UV intensity at z = 5 is unchanged at higher redshifts, the reionization epoch is estimated to be z_<reion> > 7- However, the Lya absorption is not appropriate to determine the reionization epoch more accurately, because Lyα is too strongly depleted even if the mean neutral fraction is less than 10^<-2>.Therefore, three conditions are required for a line in order to investigate the universe at z > 5 : (1) line emission is detectable, (2) it has lower line opacity than Lya, and (3) it has lower extinction against dust because young star-forming galaxies are often dust-enshrouded. The most favorable solution is Ha absorption lines. Actually, we have found that the Ha continuum depression traces the reionization history more accurately. Therefore, it is concluded that Ha forest is a more powerful tool to probe the universe at z > 5. The wavelengths of Ha forest drop on 3μm【less than or similar】λ_<Hα>【less than or similar】7μm at 4【less than or similar】z【less than or similar】10. Thus, the observations can be done with Subaru IRCS. Less