标题： 变化中的活动星系核（AGN）族群 显示英文标题

标题： The Changing AGN Population

摘要： 我们研究了活动星系核（AGN）群体中宽线源的比例如何随X射线光度和红移而变化。 首先，我们利用Chandra的Lockman Hole-Northwest广域数据、Chandra Deep Field-North 2Ms数据、其他Chandra深场数据以及ASCA大天区巡天数据，在z=0.1-1范围内构建了静止框架下的硬能段（2-8 keV）X射线光度函数（HXLF）。 我们发现宽线AGNs在超过3×10⁴³ erg/s时占主导地位，并且平均光度为1.3×10⁴⁴ erg/s。II型AGNs只能在类似Seyfert的X射线光度下成为X射线群体的重要组成部分。 接着，我们构建了z=0.1-0.5和z=0.5-1的HXLF，并将其与从HEAO-1 A2巡天数据测量的局部HXLF以及从软能段（0.5-2 keV）Chandra和ROSAT数据测量的z=1.5-3 HXLF进行了比较。 我们发现>1×10⁴⁴ erg/s（类星体）的源数密度随着红移减小而稳步下降，而1×10⁴³-1×10⁴⁴ erg/s源的数密度在z=0.5-1处达到峰值。然而，引人注目的是，宽线AGNs的数密度随着红移的变化大致保持恒定，但它们的平均光度在较低红移处下降，展示了另一种宇宙规模缩小的例子。 显示英文摘要

摘要： We investigate how the fraction of broad-line sources in the AGN population changes with X-ray luminosity and redshift. We first construct the rest-frame hard-energy (2-8 keV) X-ray luminosity function (HXLF) at z=0.1-1 using Chandra Lockman Hole-Northwest wide-area data, Chandra Deep Field-North 2 Ms data, other Chandra deep field data, and the ASCA Large Sky Survey data. We find that broad-line AGNs dominate above 3e43 ergs/s and have a mean luminosity of 1.3e44 ergs/s. Type II AGNs can only become an important component of the X-ray population at Seyfert-like X-ray luminosities. We then construct z=0.1-0.5 and z=0.5-1 HXLFs and compare them with both the local HXLF measured from HEAO-1 A2 survey data and the z=1.5-3 HXLF measured from soft-energy (0.5-2 keV) Chandra and ROSAT data. We find that the number density of >1e44 ergs/s sources (quasars) steadily declines with decreasing redshift, while the number density of 1e43-1e44 ergs/s sources peaks at z=0.5-1. Strikingly, however, the number density of broad-line AGNs remains roughly constant with redshift while their average luminosities decline at the lower redshifts, showing another example of cosmic downsizing.