Suppression of dwarf galaxy formation by cosmic reionization
Suppression of dwarf galaxy formation by cosmic reionization
复制标题
宇宙再电离抑制矮星系的形成
作者：
J. Wyithe;A. Loeb
最近发现了大量在宇宙大爆炸后不到10亿年诞生的微弱星系。沿着已知最早的类星体的视线观察到，这些星系分布的波动导致了宇宙氢的电离部分在几十兆秒差距的尺度上的散射。理论模拟预测，在宇宙氢被再电离后，矮星系的形成应该被抑制，从而导致宇宙恒星形成速度的下降。在这里，我们报告了这种抑制的证据。我们表明，在红移z≈5.5处产生大部分电离辐射的后再电离星系的质量必须超过~ 1010.9±0.5太阳质量（M[圆点]），否则上述散射将比观测到的要小。这个极限质量比被认为主导宇宙氢再电离的星系质量（~ 108M[圆点]）大两个数量级。我们预测，未来的天基红外望远镜调查将探测到一群较小的星系，它们在矮星系抑制时代之前的较早时间使宇宙再电离。
A large number of faint galaxies, born less than a billion years after the Big Bang, have recently been discovered. Fluctuations in the distribution of these galaxies contributed to a scatter in the ionization fraction of cosmic hydrogen on scales of tens of megaparsecs, as observed along the lines of sight to the earliest known quasars. Theoretical simulations predict that the formation of dwarf galaxies should have been suppressed after cosmic hydrogen was reionized, leading to a drop in the cosmic star-formation rate. Here we report evidence for this suppression. We show that the post-reionization galaxies that produced most of the ionizing radiation at a redshift z ≈ 5.5 must have had a mass in excess of ∼1010.9 ± 0.5 solar masses (M[circdot]) or else the aforementioned scatter would have been smaller than observed. This limiting mass is two orders of magnitude larger than the galaxy mass that is thought to have dominated the reionization of cosmic hydrogen (∼108M[circdot]). We predict that future surveys with space-based infrared telescopes will detect a population of smaller galaxies that reionized the Universe at an earlier time, before the epoch of dwarf galaxy suppression.