Evolution of neutral gas at high redshift: implications for the epoch of galaxy formation
Evolution of neutral gas at high redshift: implications for the epoch of galaxy formation
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高红移下中性气体的演化：对星系形成时代的影响
DOI：
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发表时间：
1996
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通讯作者：
M. Irwin
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作者：
L. Storrie;R. McMahon;M. Irwin
尽管观测上很少见，但阻尼 Lyα 吸收系统在宇宙中中性气体的质量密度中占主导地位。在 APM z > 4 QSO 调查的 26 个 QSO 中发现了 11 个覆盖 2.8 ≤ z ≤ 4.4 的高红移阻尼 Lyα 系统，将这些吸收系统调查扩展到目前可能的最高红移。将我们的新数据集与之前的调查相结合，我们发现中性气体中的宇宙质量密度 Ωg 在 z ∼ 2 之前并没有像之前的研究表明的那样急剧上升。观察到的 Ωg 有证据表明 z ∼ 2 处出现平坦化，并且 z ∼ 3 处可能发生翻转。当与柱密度 log NHI ≥ 21 原子 cm^(−2) 的阻尼系统的单位红移数密度 z > 3.5 时的下降相结合时，这些结果表明 z ≳ 3 处的纪元在此之前最高柱密度阻尼系统仍在形成。我们发现，在红移范围 2 < z < 4 内，中性气体的总质量与当今星系中恒星的总可见质量略有可比。然而，如果仅考虑恒星盘中可见的总质量，即排除银河核球，则这两个值具有可比性。我们正在观察中性气体的质量，其质量与可见盘状恒星的质量相当。 Lanzetta、Wolfe 和 Turnshek 发现 Ω(z ≈ 3.5) 是 Ω(z ≈ 2) 的两倍，这意味着在 z = 3.5 和 2 之间发生的恒星形成量一定比金属丰度研究表明的要多得多。这就产生了“宇宙 G 矮星问题”。我们发现 Ωg 的渐进演化缓解了这一问题。这些结果对星系形成理论具有深远的影响。
Although observationally rare, damped Lyα absorption systems dominate the mass density of neutral gas in the Universe. 11 high-redshift damped Lyα systems covering 2.8 ≤z ≤ 4.4 were discovered in 26 QSOs from the APM z > 4 QSO survey, extending these absorption system surveys to the highest redshifts currently possible. Combining our new data set with previous surveys, we find that the cosmological mass density in neutral gas, Ωg, does not rise as steeply prior to z ∼ 2 as indicated by previous studies. There is evidence in the observed Ωg for a flattening at z ∼ 2 and a possible turnover at z ∼ 3. When combined with the decline at z > 3.5 in number density per unit redshift of damped systems with column densities log NHI ≥ 21 atom cm^(−2), these results point to an epoch at z ≳ 3 prior to which the highest column density damped systems are still forming. We find that, over the redshift range 2 < z < 4, the total mass in neutral gas is marginally comparable to the total visible mass in stars in present-day galaxies. However, if one considers the total mass visible in stellar discs alone, i.e. excluding galactic bulges, the two values are comparable. We are observing a mass of neutral gas that is comparable to the mass of visible disc stars. Lanzetta, Wolfe & Turnshek found that Ω(z ≈ 3.5) was twice Ω(z ≈ 2), implying that a much larger amount of star formation must have taken place between z = 3.5 and 2 than is indicated by metallicity studies. This created a ‘cosmic G-dwarf problem’. The more gradual evolution of Ωg that we find alleviates this. These results have profound implications for theories of galaxy formation.