莱曼α发射体的奇异事例：从z ~ 3到z ~ 2的年轻化？
The Curious Case of Lyman Alpha Emitters: Growing Younger from z ~ 3 to z ~ 2?
摘要：
Lyman Alpha Emitting（LAE）星系被认为是现今L* 星系的祖先。聚类分析表明z ~ 3的LAEs可能演化为z ~ 2的LAEs，但尚不清楚这些星系的物理性质是否与这一假设相符。几个研究小组已经研究了LAEs的性质，使用光谱能量分布（SED）拟合，但直接比较他们的结果是复杂的不一致的数据处理和建模的恒星星族，这是退化的星系演化的影响的假设。通过使用相同的数据分析管道和SED拟合软件在z = 3.1和z = 2.1的LAEs的两个堆叠样本，并通过消除几个系统的不确定性，可能会导致差异，我们确定这两个星系样本的物理性质是显着不同的。发现z = 3.1的LAEs是古老的（年龄约为1 Gyr）和贫金属（Z < 0.2 Z_Sun），而z = 2.1的LAEs似乎是年轻的（年龄约为5000万年）和富金属（Z > Z_Sun）。观测到的恒星年龄的差异使得z = 3.1的LAEs不太可能直接演化为z = 2.1的LAEs。需要更大的星系样本，对单个物体的研究和在这些红移处对金属丰度的光谱测量来证实这一图像，这很难与1 Gyr宇宙演化的影响相一致。
英文摘要：
Lyman Alpha Emitting (LAE) galaxies are thought to be progenitors of present-day L* galaxies. Clustering analyses have suggested that LAEs at z ~ 3 might evolve into LAEs at z ~ 2, but it is unclear whether the physical nature of these galaxies is compatible with this hypothesis. Several groups have investigated the properties of LAEs using spectral energy distribution (SED) fitting, but direct comparison of their results is complicated by inconsistencies in the treatment of the data and in the assumptions made in modeling the stellar populations, which are degenerate with the effects of galaxy evolution. By using the same data analysis pipeline and SED fitting software on two stacked samples of LAEs at z = 3.1 and z = 2.1, and by eliminating several systematic uncertainties that might cause a discrepancy, we determine that the physical properties of these two samples of galaxies are dramatically different. LAEs at z = 3.1 are found to be old (age ~ 1 Gyr) and metal-poor (Z < 0.2 Z_Sun), while LAEs at z = 2.1 appear to be young (age ~ 50 Myr) and metal-rich (Z > Z_Sun). The difference in the observed stellar ages makes it very unlikely that z = 3.1 LAEs evolve directly into z = 2.1 LAEs. Larger samples of galaxies, studies of individual objects and spectroscopic measurements of metallicity at these redshifts are needed to confirm this picture, which is difficult to reconcile with the effects of 1 Gyr of cosmological evolution.
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