Black holes across a broad range of masses play a key role in the evolution of galaxies. The initial seeds of black holes formed at $z \sim 30$ and grew over cosmic time by gas accretion and mergers. Using observational data for quasars and theoretical models for the hierarchical assembly of dark matter halos, we study the relative importance of gas accretion and mergers for black hole growth, as a function of redshift ($0 10^8 \, \mathrm{M_{\odot}}$ and $z>6$; and (ii) growth by mergers is dominant at $M_{\bullet} 5.5$, and at $M_{\bullet} > 10^8 \, \mathrm{M_{\odot}}$ and $z<2$. As the growth channel has direct implications for the black hole spin (with gas accretion leading to higher spin values), we test our model against $\sim 20$ robust spin measurements available thus far. As expected, the spin tends to decline toward the merger-dominated regime, thereby supporting our model. The next generation of X-ray and gravitational-wave observatories (e.g. Lynx, AXIS, Athena and LISA) will map out populations of black holes up to very high redshift ($z\sim 20)$, covering the parameter space investigated here in almost its entirety. Their data will be instrumental to providing a clear picture of how black holes grew across cosmic time.

中文翻译：

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用 X 射线和引力波观测分离黑洞宇宙增长中的吸积和合并

质量范围广泛的黑洞在星系的演化中起着关键作用。黑洞的初始种子在 $z \sim 30$ 形成，并通过气体吸积和合并在宇宙时间内成长。使用类星体的观测数据和暗物质晕分层组装的理论模型，我们研究了气体吸积和合并对黑洞增长的相对重要性，作为红移的函数 ($0 10^8 \, \mathrm{M_{\ odot}}$ 和 $z>6$；以及 (ii) 合并增长在 $M_{\bullet} 5.5$ 和 $M_{\bullet} > 10^8 \, \mathrm{M_{\ odot}}$ 和 $z<2$。由于增长通道对黑洞自旋有直接影响（气体吸积导致更高的自旋值），我们根据迄今为止可用的 $\sim 20$ 稳健自旋测量来测试我们的模型. 正如预期的那样，自旋趋向于以合并为主导的制度，从而支持我们的模型。下一代 X 射线和引力波天文台（例如 Lynx、AXIS、Athena 和 LISA）将绘制出红移非常高 ($z\sim 20)$ 的黑洞群，涵盖此处研究的参数空间几乎全部。他们的数据将有助于提供关于黑洞如何跨越宇宙时间增长的清晰画面。