Accretion History of AGNs. III. Radiative Efficiency and AGN Contribution to Reionization
Accretion History of AGNs. III. Radiative Efficiency and AGN Contribution to Reionization
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DOI：
10.3847/1538-4357/abb815
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发表时间：
2020-09
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影响因子：
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通讯作者：
T. Ananna;C. Urry;E. Treister;R. Hickox;F. Shankar;C. Ricci;N. Cappelluti;S. Marchesi;T. Turner-T.
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作者：
T. Ananna;C. Urry;E. Treister;R. Hickox;F. Shankar;C. Ricci;N. Cappelluti;S. Marchesi;T. Turner-T.
超大质量黑洞（SMBH）生长的宇宙历史对于理解星系演化、再电离和吸积物理是非常重要的。最近的努斯塔、Swift-BAT和Chandra硬X射线巡天对严重遮蔽的活动星系核（AGN）的空间密度提供了新的限制。使用新的X射线光度函数从这些数据中得出，我们在这里估计的吸积效率的SMBHs和它们的再电离的贡献。根据X射线辐射和遮蔽柱密度的分布，转换成紫外线波长，我们计算了活动星系核的总电离辐射随红移的变化。将光度函数限制在无遮蔽活动星系核上，我们的结果与目前无遮蔽活动星系核的紫外光度函数一致。对于逃逸分数的现实假设，所有活动星系核对宇宙再电离的贡献比星系贡献（在z = 6时为23%）低2.4倍。我们的研究结果还提供了一个观测约束的处方，可用于星系演化的模拟或模型。为了估计SMBHs将质量转换为光的平均效率，我们将使用热辐射校正从X射线光转换的总辐射能量与最近的局部黑洞质量密度进行比较。最有可能的值η = 0.3-0.34，接近最大旋转克尔黑洞的理论极限η = 0.42，这意味着平均而言，生长的SMBH正在快速旋转。
The cosmic history of supermassive black hole (SMBH) growth is important for understanding galaxy evolution, reionization, and the physics of accretion. Recent NuSTAR, Swift-BAT, and Chandra hard X-ray surveys have provided new constraints on the space density of heavily obscured active galactic nuclei (AGNs). Using the new X-ray luminosity function derived from these data, we here estimate the accretion efficiency of SMBHs and their contribution to reionization. We calculate the total ionizing radiation from AGNs as a function of redshift, based on the X radiation and distribution of obscuring column density, converted to ultraviolet (UV) wavelengths. Limiting the luminosity function to unobscured AGNs only, our results agree with current UV luminosity functions of unobscured AGNs. For realistic assumptions about the escape fraction, the contribution of all AGNs to cosmic reionization is ∼4 times lower than the galaxy contribution (23% at z ∼ 6). Our results also offer an observationally constrained prescription that can be used in simulations or models of galaxy evolution. To estimate the average efficiency with which SMBHs convert mass to light, we compare the total radiated energy, converted from X-ray light using a bolometric correction, with the most recent local black hole mass density. The most likely value, η ∼ 0.3–0.34, approaches the theoretical limit for a maximally rotating Kerr black hole, η = 0.42, implying that on average growing SMBHs are spinning rapidly.