高红移低光度活动星系核的研究进展

摘要

The studies of Active Galactic Nuclei (AGNs) at high redshifts (z ≈ 3) have been mostly limited to color selected quasars (QSOs).QSOs are bright and have point-like morphologies,making them easy to be selected in imaging surveys.However,QSOs are the minorities in the full AGN population,as is well studied in the luminosity function of AGNs.The majority of the AGN population-the low-luminosity AGNs (hereafter LLAGNs)-remains largely inaccessible.Throughout this paper,we refer to AGNs that are at least one or two magnitudes fainter than the SDSS-Ⅲ/BOSS QSOs as LLAGNs.Particularly,the surveys with LLAGNs should be 23 ～ 24 AB mag deep in g-band (-24 ～ Mg[z =3] mag-1 (≦)-23) or deeper (the limiting magnitude for the SDSS-Ⅲ/BOSS survey is r ＜ 21.85 mag or g ＜ 22 mag)[10].LLAGNs are important,for example,for the purpose of constraining the faint end of the luminosity function of AGNs,studying the differences in the fueling mechanisms between weak and strong AGNs,and exploring the potential relationship between supermassive black holes and the large-scale structure in which their host galaxies reside.The sky coverages and the sample sizes of current deep surveys that contain LLAGNs at z ≈ 3 are limited ((≦) 2 deg2,(≈) 102).In this paper,we present both photometric and spectroscopic surveys that include LLAGN samples at z (≈) 3.We also introduce the HETDEX survey,which will be online in 2017 and will observe more than 104 low-luminosity type 1 AGNs at 2 ＜ z ＜ 4.We summarize these surveys according to their luminosity functions,clustering,and Eddington ratios.To better show the power of studies on the clustering of AGNs,we include the results of the clustering of LLAGNs at low redshifts,in addition to those at high redshifts,that are based on relatively limited samples.%低光度活动星系核(Low-Luminosity AGN,简称为LLAGN)指比斯隆数字化巡天第三期SDSS-Ⅲ/BOSS类星体(quasar,QSO)暗大约1～2 mag的活动星系核,如g波段探测极限达到23～24AB mag,约对应Mg[z=3]≈-24～-23 mag.现有的高红移巡天中包含的LLAGN样本还比较有限.从测光巡天和光谱巡天两方面总结已经开展的包含高红移(z≈3) LLAGN样本的深场星系巡天项目,并简单介绍一个刚刚开展的HETDEX巡天项目(该巡天项目将观测到约104个Ⅰ型LLAGN,其z≈3,g＜24 mag).从光度函数、成团性以及爱丁顿吸积率等方面对目前高红移LLAGN的研究进行了总结.由于高红移AGN成团性的研究较为有限,为了更好地解释成团性研究的科学意义,也对低红移AGN在成团性方面的研究进行了介绍.