We study the stellar and star formation (SF) properties of the host galaxies of 58 X-ray selected AGN in the GOODS portion of the Chandra Deep Field South (CDF-S) region at z~0.5-1.4. The AGN are selected such that their rest-frame UV to near-IR SEDs are dominated by stellar emission, i.e., they show a prominent 1.6micron bump, thus minimizing the AGN emission 'contamination'. This AGN population comprises approximately 50% of the X-ray selected AGN at these redshifts. Using models of stellar and dust emission we model their SEDs to derive stellar masses (M*) and total (UV+IR) star formation rates (SFR). AGN reside in the most massive galaxies at the redshifts probed here. Their characteristic stellar masses (M*~7.8x10^10 Msun and M*~1.2x10^11 Msun at median z of 0.67 and 1.07, respectively) appear to be representative of the X-ray selected AGN population at these redshifts, and are intermediate between those of local type 2 AGN and high redshift (z~2) AGN. The inferred black hole masses (MBH~ 2x10^8 Msun) of typical AGN are similar to those of optically identified quasars at similar redshifts. Since the AGN in our sample are much less luminous (L(2-10keV)<10^44 erg/s) than quasars, typical AGN have low Eddington ratios (eta~0.01-0.001). This suggests that, at least at intermediate z, the cosmic AGN 'downsizing' is due to both a decrease in the characteristic stellar mass of typical host galaxies, and less efficient accretion. Finally there is no strong evidence in AGN host galaxies for either highly suppressed SF (expected if AGN played a role in quenching SF) or elevated SF when compared to mass selected (i.e., IRAC-selected) galaxies of similar stellar masses and redshifts. This may be explained by the fact that galaxies with M*~5x 10^10 - 5x10^11 Msun are still being assembled at the redshifts probed here.
我们使用HST/ACS图像和COSMOS场的光度表来分析大约400个活动星系核候选者在红移0.3 < z < 1.0的宿主星系的形态。我们比较了活动星系核主机与非活动星系的样本从宇宙领域相匹配的幅度和红移分布的活动星系核主机。我们执行2-D表面亮度建模与GALFIT产生主机星系和核点源的幅度。X射线选择的活动星系核宿主星系的形态跨越了相当大的范围，峰值之间的早期型，隆起为主和晚期型，磁盘为主的系统。我们还测量了宿主星系的不对称性和浓度。未考虑到，核点源可以显着偏差的结果，这些测量的结构参数，所以我们减去最佳拟合点源组件，以获得图像的基础主机星系。我们的浓度测量结果加强了我们的2-D形态拟合的结果，将X射线活动星系核主机之间的早期和晚期类型的不活跃星系。活动星系核宿主的不对称性分布与控制星系一致。再加上活动星系核周围缺乏多余的伴星系，这种不对称分布表明活动星系核中的强相互作用并不比正常星系中的强。根据最近的工作，这些结果表明，在这些X射线光度的活动星系核的宿主星系可能是在一个过渡，从磁盘为主的膨胀为主，但这种过渡通常不是由重大合并触发。
Understanding AGN-Host Connection in Partially Obscured Active Galactic Nuclei. Part I: The Nature of AGN+HII Composites
我们的系列论文的目标是研究活动星系核和恒星形成之间的进化联系，在其宿主星系的部分模糊活动星系核（即，Seyfert 1.8和1.9星系）。利用这些星系，可以通过直接测量来研究这两个组成部分的性质。本文主要研究位于[NII]/Ha vs. [OIII]/Hb图中理论分离线和经验分离线之间的宽线复合星系（复合活动星系核）。这些星系是从SDSS DR 4 MPA/JHU星表提供的复合星系中寻找的。在重新分析光谱后，我们根据BPT图对85个复合活动星系核进行了精细分类。位于三条理论分离线以下的所有天体都与年轻的恒星星族（<1 Gyrs）有关，而在单个多重分类天体中，可以识别出年轻或年老的恒星星族。在[OI]/Ha与[OIII]/Hb图中，具有非常古老的恒星星族的多重分类天体位于LINER区域。然后，我们考虑活动星系核和恒星形成之间的联系，得出的关键结果。由宽Ha辐射推断的Eddington比、由D_n（4000）估算的活动星系核宿主恒星星族年龄和谱线比[OI]/Ha之间存在一定的相关性。这些关系强有力地支持了活动星系核随着年轻恒星星族的老化和衰落而从具有软谱的高L/LEdd态演化到具有硬谱的低L/LEdd态的演化过程。谱线比[OI]/Ha与D_n（4000）之间的显著相关性表明，谱线比可以用来追踪I型活动星系核中恒星星族的年龄。
