The early stage in the formation of a galaxy inevitably involves a spatially extended distribution of infalling, cold gas. If a central luminous quasar turned on during this phase, it would result in significant extended Lyα emission, possibly accompanied by other lines. For halos condensing at redshifts 3 z 8 and having virial temperatures 2 × 105 K Tvir 2 × 106 K, this emission results in a "fuzz" of characteristic angular diameter of a few arcseconds and surface brightness ~10-18 to 10-16 ergs s-1 cm-2 arcsec-2. The fuzz around bright, high-redshift quasars could be detected in deep narrowband imaging with current telescopes, providing a direct constraint on galaxy formation models. The absence of detectable fuzz might suggest that most of the protogalaxy's gas settles to a self-gravitating disk before a quasar turns on. However, continued gas infall from large radii, or an on-going merger spreading cold gas over a large solid angle, during the luminous quasar phase could also result in extended Lyα emission, and can be constrained by deep narrowband imaging.
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机译：星系形成的早期不可避免地会涉及到进入的冷气体的空间扩展分布。如果在此阶段打开了一个中央发光类星体，它将导致明显延长的Lyα发射，并可能伴有其他谱线。对于光晕在红移3 z 8时冷凝并且病毒温度为2×105 K Tvir 2×106 K的情况，这种发射会导致特征角直径为几弧秒且表面亮度约为10-18至10-16 erg的“模糊” s-1 cm-2 arcsec-2。明亮的，高红移类星体周围的绒毛可以用当前的望远镜在深窄带成像中检测到，这直接限制了星系形成模型。缺乏可检测到的模糊现象可能表明，原恒星系中的大多数气体在类星体开启之前就已经沉降到了自重盘上。但是，在发光类星体阶段，大半径的连续气体侵入或持续不断的合并将冷气散布在较大的立体角上，也可能导致Lyα发射时间延长，并可能受到深窄带成像的限制。
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