标题： 中性氢都去哪儿了？ 显示英文标题

标题： Where has all the neutral hydrogen gone?

摘要： 我们对河外HI（HIDEEP）的极端深度调查没有发现星际气体云，也没有发现HI在推断的全局柱密度低于10^20 cm^-2的星系，而我们本可以检测到柱密度低至4 x 10^18 cm^-2的天体。 我们推测低表面密度的氢要么被电离，要么被冻结在“冻结盘”中，即局部Ly-alpha不足以激发21厘米跃迁到高于宇宙背景的自旋温度的结构。 这些“冻结盘”可能是许多QSO ALSs的原因。 显示英文摘要

摘要： Our extremely deep survey for extragalactic HI (HIDEEP) finds no intergalactic gas clouds, and no galaxies with HI at inferred global column-densities below 10^20 cm^-2 when we could have detected such objects down to a completeness limit of 4 x 10^18 cm^-2. We speculate that low surface-density hydrogen is either ionised or locked up in ``frozen discs'', i.e. structures where the local Ly-alpha is insufficient to excite the 21-cm transition to a spin-temperature above the cosmic background. Such ``frozen discs'' might be responsible for many QSOALSs.