汉堡/欧洲南方天文台巡天中的低红移AGN：II。活动黑洞质量函数和爱丁顿比分布函数
Low redshift AGN in the Hamburg/ESO Survey: II. The active black hole mass function and the distribution function of Eddington ratios
摘要：
我们估计黑洞的质量和爱丁顿比的一个定义良好的本地（z <0.3）宽线AGN从汉堡/ESO调查（HES）的样本，基于H β线和标准配方假设维里平衡的宽线区域。该样本代表了从塞弗特1星系到发光类星体的广泛光度范围内的低红移活动星系核人口。从黑洞质量的分布出发，利用HES具有一个定义良好的选择函数的事实，导出了局域宇宙中的活动黑洞质量函数（BHMF）和爱丁顿比分布函数（ERDF）.虽然直接测定的ERDF在L/L_Edd~0.1附近翻转，与先前分析中所见相似，但我们认为这是样本选择的人为因素。我们采用极大似然方法，在充分考虑样本选择函数的情况下，无偏地同时估计了黑洞质量和爱丁顿比的内禀分布函数.由此产生的ERDF很好地描述了一个Schechter函数，有证据表明，一个稳定的增加，向低爱丁顿比，定性相似，已发现的2型活动星系核从SDSS。比较我们的最佳拟合的活动BHMF与不活动的黑洞的质量函数，我们得到的活动黑洞的分数的估计，即活动星系核占空比的估计。随着黑洞质量的增加，活动部分强烈减少。与BHMF在更高红移处的比较也表明，在高质量端，黑洞现在处于比早期宇宙时代更不活跃的阶段。我们的结果支持了黑洞反分层生长的概念，并且与宇宙早期质量最大的黑洞生长的图像一致，而目前主要是质量较小的黑洞以显着的速度增生。
英文摘要：
We estimated black hole masses and Eddington ratios for a well defined sample of local (z<0.3) broad line AGN from the Hamburg/ESO Survey (HES), based on the Hbeta line and standard recipes assuming virial equilibrium for the broad line region. The sample represents the low-redshift AGN population over a wide range of luminosities, from Seyfert 1 galaxies to luminous quasars. From the distribution of black hole masses we derived the active black hole mass function (BHMF) and the Eddington ratio distribution function (ERDF) in the local universe, exploiting the fact that the HES has a well-defined selection function. While the directly determined ERDF turns over around L/L_Edd ~ 0.1, similar to what has been seen in previous analyses, we argue that this is an artefact of the sample selection. We employed a maximum likelihood approach to estimate the intrinsic distribution functions of black hole masses and Eddington ratios simultaneously in an unbiased way, taking the sample selection function fully into account. The resulting ERDF is well described by a Schechter function, with evidence for a steady increase towards lower Eddington ratios, qualitatively similar to what has been found for type~2 AGN from the SDSS. Comparing our best-fit active BHMF with the mass function of inactive black holes we obtained an estimate of the fraction of active black holes, i.e. an estimate of the AGN duty cycle. The active fraction decreases strongly with increasing black hole mass. A comparison with the BHMF at higher redshifts also indicates that, at the high mass end, black holes are now in a less active stage than at earlier cosmic epochs. Our results support the notion of anti-hierarchical growth of black holes, and are consistent with a picture where the most massive black holes grew at early cosmic times, whereas at present mainly smaller mass black holes accrete at a significant rate.
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