[论文解读] Local Black Hole Scaling Relations Imply Compton Thick or Super Eddington Accretion

Gregory S. Novak|arXiv (Cornell University)|Oct 14, 2013

Astrophysical Phenomena and Observations被引用 6

一句话总结

本文认为，修订后的局部黑洞质量关系（将有效质量归一化从0.1%提高到0.5%的星系盘质量）表明，黑洞吸积的平均辐射效率远低于薄盘模型预期的最小值，因此必须通过康普顿厚遮蔽或超爱丁顿吸积来解释质量预算的缺失。关键结果是，超爱丁顿吸积强烈支持以解决z=7类星体快速增长的矛盾。

ABSTRACT

A recent analysis of black hole scaling relations, used to estimate the local mass density in black holes, has indicated that the normalization of the scaling relations should be increased by approximately a factor of five. The local black hole mass density is connected to the mean radiative efficiency of accretion through the time integral of the quasar volume density. The correspondence between this estimate of the radiative efficiency and that expected theoretically from thin-disk accretion has long been used as an argument that most of the growth in black holes occurs via luminous accretion. The increase of the mass density in black holes pushes the mean observed radiative efficiency to values below that expected for thin-disk accretion for any value of the black hole spin, including retrograde accretion disks. This can be accommodated via black hole growth channels that are intrinsically radiatively inefficient, such as super-Eddington accretion, or via growth channels that are intrinsically radiatively efficient but for which few of the photons are observed, such as Compton thick accretion. Measurements of the 30 keV peak in the X-ray background indicate a significant population of Compton thick sources which can explain some, but not all, of the change in the local black hole mass density. If this result is taken as evidence that super-Eddington accretion is common, it greatly reduces the tension associated with the growth timescale of observed z=7 quasars compared to the age of the universe at that redshift.

研究动机与目标

• 基于Kormendy & Ho (2013)提供的更新版关系，重新评估本地黑洞质量密度。
• 评估观测到的平均辐射效率与薄盘吸积理论预期的一致性。
• 确定康普顿厚吸积或超爱丁顿吸积是否能解释观测到的与预期吸积效率之间的差异。
• 解决高红移z=7类星体增长 timescale 的矛盾。

提出的方法

• 使用更新后的M_BH–M_bulge关系归一化（0.5%而非0.1%）重新计算本地黑洞质量密度。
• 应用Soltan论证，将时间积分的类星体光度函数与本地黑洞质量函数联系起来。
• 通过积分光度密度与本地质量密度的比值计算平均辐射效率。
• 将推导出的平均效率与薄盘吸积的理论极限（3.7%至42%）以及非旋转黑洞的理论极限（5.7%）进行比较。
• 利用X射线背景在30 keV处的峰值评估康普顿厚源的贡献。
• 评估超爱丁顿吸积是否能解释观测到的辐射效率不足。

实验结果

研究问题

• RQ1 基于更新的标定关系，本地黑洞质量密度的修订估计值是多少？
• RQ2 推导出的平均辐射效率是否低于薄盘吸积的理论最小值？
• RQ3 康普顿厚吸积是否足以解释辐射效率的差异？
• RQ4 是否需要超爱丁顿吸积来调和观测到的质量密度与吸积物理之间的矛盾？
• RQ5 修订后的效率如何影响z=7类星体的增长 timescale？

主要发现

• 当M_BH–M_bulge关系的归一化从0.1%提高到0.5%的星系盘质量时，本地黑洞质量密度提高了五倍。
• 推导出的平均辐射效率从6.5%下降至1.3%，低于非旋转黑洞的理论最小值5.7%。
• 仅靠康普顿厚吸积无法完全解释观测到的辐射效率不足，因为X射线背景数据表明其仅能解释五倍增长中的一部分。
• 低效率表明，大多数黑洞增长通过本质上辐射效率低下或观测上被隐藏的吸积模式发生。
• 超爱丁顿吸积被强烈支持为解释观测到的低效率并解决z=7类星体增长 timescale 矛盾的机制。
• 若存在超爱丁顿吸积的证据，将显著缩短z=7类星体所需的生长 timescale，使其与该红移处宇宙年龄一致。