Assessing the redshift evolution of massive black holes and their hosts
Assessing the redshift evolution of massive black holes and their hosts
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评估大质量黑洞及其宿主的红移演化
DOI：
--
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
D. Stark
中科院分区：
文献类型：
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作者：
M. Volonteri;D. Stark
基于最近对高红移黑洞的观测结果，我们探讨了散射和观测偏差对恢复高红移黑洞群固有特性的影响。我们发现，分散和选择偏差可以隐藏黑洞与其宿主之间的内在相关性，整个种群的“可观察”子样本表明，平均而言，即使潜在种群的特征是没有进化或负进化，也会出现正进化。我们创建了黑洞的理论质量函数，将暗物质晕的质量函数与黑洞与其宿主的标准关系进行卷积。在这些假设下，我们发现局部MBH -σ相关性不能拟合由Willott等人提出的z = 6黑洞质量函数，过高估计了除了质量最大的黑洞之外的所有黑洞的数量密度。正演化或在MBH -σ相关中包含散射使差异更大，因为它进一步增加了可观测黑洞的数量密度。我们注意到，如果MBH -σ相关性atz = 6比现在更陡峭，那么质量函数就会变得更浅。这有助于再现Willott等人提出的z = 6黑洞的质量函数。另一种可能是，极少量的光晕（1/1000数量级）在z = 6处拥有一个活跃的大质量黑洞，或者大多数AGN被遮挡，阻碍了它们在光学调查中的探测。如果活跃部分或光度是宿主或黑洞质量的函数，那么目前对高红移黑洞质量函数的测量可能低估了低质量黑洞的密度。最后，我们讨论了在高红移时可能导致更陡峭的MBH -σ关系的物理情形。
Motivated by recent observational results that focus on high-redshift black holes, we explore the effect of scatter and observational biases on the ability to recover the intrinsic properties of the black hole population at high redshift. We find that scatter and selection biases can hide the intrinsic correlations between black holes and their hosts, with ‘observable’ subsamples of the whole population suggesting, on average, positive evolution even when the underlying population is characterized by no or negative evolution. We create theoretical mass functions of black holes convolving the mass function of dark matter haloes with standard relationships linking black holes with their hosts. Under these assumptions, we find that the local MBH–σ correlation is unable to fit the z = 6 black hole mass function proposed by Willott et al., overestimating the number density of all but the most massive black holes. Positive evolution or including scatter in the MBH–σ correlation makes the discrepancy worse, as it further increases the number density of observable black holes. We note that if the MBH–σ correlation atz = 6 is steeper than today, then the mass function becomes shallower. This helps reproducing the mass function of z = 6 black holes proposed by Willott et al. Alternatively, it is possible that very few haloes (of order 1/1000) host an active massive black hole at z = 6, or that most AGN are obscured, hindering their detection in optical surveys. Current measurements of the high-redshift black hole mass function might be underestimating the density of low-mass black holes if the active fraction or luminosity is a function of host or black hole mass. Finally, we discuss physical scenarios that can possibly lead to a steeper MBH–σ relation at high redshift.
影响因子：
64.8
作者：
J. Kormendy;R. Bender
通讯作者：
J. Kormendy;R. Bender