Quasars at cosmic dawn provide powerful probes of the formation and growth of the earliest supermassive black holes (SMBHs) in the Universe, their connections to galaxy and structure formation, and the evolution of the intergalactic medium (IGM) at the epoch of reionization (EoR). Hundreds of quasars have been discovered in the first billion years of cosmic history, with the quasar redshift frontier extended to z ∼ 7.6. Observations of quasars at cosmic dawn show the following: ▪The number density of luminous quasars declines exponentially at z > 5, suggesting that the earliest quasars emerge at z ∼ 10; the lack of strong evolution in their average spectral energy distribution indicates a rapid buildup of the active galactic nucleus environment.▪Billion-solar-mass black holes (BHs) already exist at z > 7.5; they must form and grow in less than 700 Myr, by a combination of massive early BH seeds with highly efficient and sustained accretion.▪The rapid quasar growth is accompanied by strong star formation and feedback activity in their host galaxies, which show diverse morphological and kinetic properties, with typical dynamical mass lower than that implied by the local BH/galaxy scaling relations.▪Hi absorption in quasar spectra probes the tail end of cosmic reionization at z ∼ 5.3–6 and indicates the EoR midpoint at 6.9 < z < 7.6, with large spatial fluctuations in IGM ionization. Observations of heavy element absorption lines suggest that the circumgalactic medium also experiences evolution in its ionization structure and metal enrichment during the EoR.

中文翻译：

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宇宙黎明的类星体和星际介质


宇宙黎明的类星体为宇宙中最早的超大质量黑洞 （SMBH） 的形成和生长、它们与星系和结构形成的联系以及再电离 （EoR） 时期星系际介质 （IGM） 的演化提供了有力的探针。在宇宙历史的前十亿年中，已经发现了数百个类星体，类星体红移边界扩展到 z ∼ 7.6。在宇宙黎明时对类星体的观测显示以下内容：▪发光类星体的数量密度在 z > 5 处呈指数下降，这表明最早的类星体出现在 z ∼ 10 处;它们的平均光谱能量分布缺乏强烈的演化表明活跃的星系核环境正在迅速积累.▪十亿太阳质量的黑洞 （BHs） 已经存在于 z > 7.5;它们必须在不到 700 Myr 的时间内形成和生长，由大量早期 BH 种子与高效和持续的吸积相结合。▪类星体的快速生长伴随着宿主星系中强烈的恒星形成和反馈活动，它们显示出不同的形态和动力学特性，典型的动力学质量低于局部 BH/星系缩放关系所暗示的质量。▪类星体光谱中的 Hi 吸收探测了 z 处宇宙再电离的尾端∼ 5.3–6，表示 EoR 中点位于 6.9 < z < 7.6，IGM 电离空间波动很大。对重元素吸收线的观察表明，在 EoR 期间，银河系周围介质也经历了电离结构和金属富集的演变。