Low redshift AGN in the Hamburg/ESO Survey - II. The active black hole mass function and the distribution function of Eddington ratios
Low redshift AGN in the Hamburg/ESO Survey - II. The active black hole mass function and the distribution function of Eddington ratios
复制标题
DOI：
10.1051/0004-6361/201014193
复制
发表时间：
2010-04
影响因子：
6.5
通讯作者：
A. Schulze;L. Wisotzki
中科院分区：
文献类型：
--
作者：
A. Schulze;L. Wisotzki
我们根据Hβ线和假设宽线区域维里平衡的标准公式，估算了来自汉堡/欧洲南方天文台的一个定义明确的局部(z<；0.3)宽线活动星系核样本的黑洞质量和爱丁顿比(L/LEdd)。该样本代表了从Seyfert 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数量。从黑洞质量的分布出发，利用HES具有明确的选择函数这一事实，我们导出了局部宇宙中的活动黑洞质量函数(BHMF)和爱丁顿比分布函数(ERDF)。虽然直接确定的ERDF值约为L/LEdd∼0.1%，与先前分析中看到的类似，但我们认为这是样本选择的人为因素。在充分考虑样本选择函数的情况下，我们采用极大似然方法无偏地同时估计黑洞质量和爱丁顿比的内禀分布函数。由此产生的ERDF可以用谢克特函数很好地描述，有证据表明朝着较低的爱丁顿比率稳步增加，定性上类似于从SDSS中发现的2型AGN。将我们最适合的活动黑洞质量函数与非活动黑洞的质量函数进行比较，我们得到了活动黑洞比例的估计值，即活动星系核占空比的估计值。活性分数随黑洞质量的增加而急剧下降。与红移较高的BHMF的比较也表明，在高质量端，黑洞现在处于不太活跃的阶段，而不是在早期的宇宙时期。我们的结果支持黑洞反等级增长的概念，并与大多数质量最大的黑洞在早期宇宙时代增长的图景一致，而目前主要是较小的质量黑洞以显著的速度增长。
We estimated black hole masses and Eddington ratios (L/LEdd) for a well defined sample of local (z < 0.3) broad line AGN from the Hamburg/ESO Survey (HES), based on the Hβ 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 distributionof black hole masses we derived theactive 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/LEdd ∼ 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.