大质量黑洞生长的精确约束
Toward precise constraints on growth of massive black holes
摘要：
星系中心大质量黑洞的生长主要来自于它们的类星体/活动星系核阶段的气体吸积。在本文中，我们应用一个扩展的Soltan参数，连接本地MBH质量函数与时间积分的类星体光度函数，MBH和类星体的人口从最近的光学和X射线调查，并获得强大的约束的光度演化（或质量增长历史）的个别类星体（或MBH）。我们发现，光度演化可能包含两个阶段：一个是由爱丁顿极限决定的初始指数增长阶段，另一个是由盘吸积的自相似长期演化决定的光度随时间呈幂律下降（斜率为-1.2--1.3）的阶段。既不可能出现只涉及具有单一爱丁顿比的增加阶段的演化，也不可能出现第二阶段的指数下降模式。类星体以高于其峰值10%的光度辐射的周期约为（2-3）x10^8年，在此期间MBH获得其质量的80%。质量到能量的转换效率是$0.16\pm0.04 ^{+0.05}_{-0}$，后者的误差占最大的不确定性，由于康普顿厚的活动星系核。从约束的光度演化类星体的预期爱丁顿比集群在一个单一的值接近0.5-1的高光度类星体和扩展到一个广泛的低光度的值。高光度类星体的爱丁顿比似乎与通过使用类星体中MBH的维里质量估计器从观测中估计的值（~0.25）相冲突，除非估计器系统地高估MBH质量2-4倍。我们还推断光学遮蔽类星体的比例约为60- 80%。本文还讨论了类星体光度演化的进一步应用。
英文摘要：
Growth of massive black holes (MBHs) in galactic centers comes mainly from gas accretion during their QSO/AGN phases. In this paper we apply an extended Soltan argument, connecting the local MBH mass function with the time-integral of the QSO luminosity function, to the demography of MBHs and QSOs from recent optical and X-ray surveys, and obtain robust constraints on the luminosity evolution (or mass growth history) of individual QSOs (or MBHs). We find that the luminosity evolution probably involves two phases: an initial exponentially increasing phase set by the Eddington limit and a following phase in which the luminosity declines with time as a power law (with a slope of -1.2--1.3) set by a self-similar long-term evolution of disk accretion. Neither an evolution involving only the increasing phase with a single Eddington ratio nor an exponentially declining pattern in the second phase is likely. The period of a QSO radiating at a luminosity higher than 10% of its peak value is about (2-3)x10^8 yr, during which the MBH obtains ~80% of its mass. The mass-to-energy conversion efficiency is $0.16\pm0.04 ^{+0.05}_{-0}$, with the latter error accounting for the maximum uncertainty due to Compton-thick AGNs. The expected Eddington ratios in QSOs from the constrained luminosity evolution cluster around a single value close to 0.5-1 for high-luminosity QSOs and extend to a wide range of lower values for low-luminosity ones. The Eddington ratios for high luminosity QSOs appear to conflict with those estimated from observations (~0.25) by using some virial mass estimators for MBHs in QSOs unless the estimators systematically over-estimate MBH masses by a factor of 2-4. We also infer the fraction of optically obscured QSOs ~60-80%. Further applications of the luminosity evolution of individual QSOs are also discussed.
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