Evolution of Galaxies in the Young Universe

本研究旨在研究星暴星系的光谱能量分布，为在宇宙学距离上有效发现原始星系提供一种途径。首先建立了星系SED演化的演化综合模型，在一定的星星形成历史方案下，求解了尘埃和恒星的辐射场以及气体-恒星系统的化学富集。将该模型应用于紫外选择星系（UVSBGs）和超亮红外星系（ULIRGs），我们发现，尽管这些星系的SED表现出相当大的变化，但这并不像以前所认为的那样是由于爆发年龄的扩散，而是由于星星形成区的致密性的差异。更活跃的星暴区域往往更紧凑，并被更密集的尘埃所掩盖。我们还发现，星暴区并没有完全被尘埃覆盖，相反，光子从内部深处泄漏，并显着影响的表面特征的SED。如果不对这些效应进行精确测量，那么推断星星形成区的年龄、光学厚度和大小就毫无意义。这项研究表明，星爆是双峰的。较弱的爆发应该是由气体盘的引力不稳定性引起的，而非常强烈的爆发可能是由外部动力学扰动，如星系-星系合并引发的。年轻宇宙中的恒星爆发也是双峰的，这是非常合理的;因此，当我们在非常大的红移下分析原始星系的SED时，需要谨慎。本研究将提供一个基本的见解，一旦观测数据的高z星系成为新一代的空间望远镜和远红外，亚毫米干涉仪。

This study aimed for to investigating the spectral energy distribution (SED) of starburst galaxies to establish a way to discover efficiently primeval galaxies at cosmological distances. First we built up an evolutionary synthesis model for the SED evolution of galaxies that solves radiation field by dust and stars as well as chemical enrichment of gas-stellar system under a certain scheme of star formation history. Applying the model to UV-selected (UVSBGs) and ultra-luminous IR (ULIRGs) galaxies, we have found that although the SEDs of these galaxies show a rather wide variety, this is not due to a spread in the burst age, as was supposed before, but due to a difference in the compactness of star forming region. More active starburst regions tend to be more compact and be obscured by denser dust. We also find that starburst regions are not entirely covered by the dust, instead photons are leaking from the deep inside and influence significantly the apparent feature of SEDs. Without precise measurements of these effects, it is rather meaningless to derive age, optical depth, and size of the star forming regions. This study suggests that starbursts are bimodal. Weaker bursts should be induced by gravitational instability of gaseous disk, while very intensive bursts are likely to be triggered by external dynamical disturbances such as galaxy-galaxy mergings. It is very much plausible that starbursts in the young universe are also bimodal; thus a caution is required when we analyze the SEDs of primeval galaxies at very large redshifts. The present study will provide a fundamental insight, once observational data of high-z galaxies become available with new generation space telescopes and far-infrared, submm interferometers.