We report that Lyα-emitting galaxies (LAEs) may not faithfully trace the cosmic web of neutral hydrogen (H i), but their distribution is likely biased depending on the viewing direction. We calculate the cross-correlation function (CCF) between galaxies and Lyα forest transmission fluctuations on the near and far sides of the galaxies separately, for three galaxy samples at z ∼ 2: LAEs, [O iii] emitters (O3Es), and continuum-selected galaxies. We find that only LAEs have anisotropic CCFs, with the near side one showing lower signals up to r = 3–4 h ⁻¹ comoving Mpc. This means that the average H i density on the near side of LAEs is lower than that on the far side by a factor of 2.1 under the fluctuating Gunn–Peterson approximation. Mock LAEs created by assigning Lyα equivalent width () values to O3Es with an empirical relation also show similar, anisotropic CCFs if we use only objects with higher than a certain threshold. These results indicate that galaxies on the far side of a dense region are more difficult to be detected (“hidden”) in Lyα because Lyα emission toward us is absorbed by dense neutral hydrogen. If the same region is viewed from a different direction, a different set of LAEs will be selected as if galaxies are playing hide-and-seek using H i gas. Care is needed when using LAEs to search for overdensities.

我们报告说，Ly α发射星系 (LAE) 可能无法忠实地追踪中性氢 (H i )的宇宙网，但它们的分布可能会因观察方向而有所偏差。我们分别计算了星系与星系近侧和远侧Ly α森林传输波动之间的互相关函数 (CCF) ，对于z ∼ 2处的三个星系样本：LAE、[O iii ] 发射体 (O3E) 和连续体选择的星系。我们发现只有 LAE 具有各向异性的 CCF，近侧的 CCF 显示较低的信号，最高r = 3–4 h ^{-1 共}移动 Mpc。这意味着平均 H i在波动的 Gunn-Peterson 近似下，LAE 近侧的密度比远侧的密度低 2.1 倍。如果我们仅使用高于某个阈值的对象，则通过将 Ly α等效宽度 ( ) 值分配给具有经验关系的 O3E创建的模拟LAE 也显示出类似的各向异性 CCF 。这些结果表明，稠密区域远端的星系更难在 Ly α 中被探测到（“隐藏”），因为向我们发射的Ly α被致密的中性氢吸收。如果从不同的方向观察同一区域，将选择一组不同的 LAE，就好像星系正在使用 H i玩捉迷藏一样气体。使用 LAE 搜索超密度时需要小心。