标题： CANDELS：通过z~2的宿主形态学约束活动星系核与合并的关系 显示英文标题

标题： CANDELS: Constraining the AGN-Merger Connection with Host Morphologies at z~2

摘要： 使用作为宇宙组装近红外深外星系遗产调查（CANDELS）一部分的哈勃空间望远镜/宽视场相机3（HST/WFC3）成像，我们研究了主要星系合并在触发红移约为2的活动星系核（AGN）活动中的作用。我们的样本包括72个中等光度（Lx ~ 1E42-1E44 erg/s）的AGN，在1.5<z<2.5范围内，这些AGN是通过Chandra深空南区的4 Msec Chandra观测选择的，这是迄今为止最深的X射线观测。采用视觉分类，我们分析了AGN宿主星系的rest-frame光学形态，并与同一红移下的216个非活跃星系的质量匹配对照样本进行了比较。我们发现大多数AGN位于盘状星系中（51.4%），而较小比例的AGN位于球状星系中（27.8%）。大约16.7%的AGN宿主具有高度扰动的形态，似乎参与了主要的合并或相互作用，而大多数宿主（55.6%）看起来相对平静且未受扰动。这些比例在统计上与对照样本中表现出类似形态扰动的星系比例一致。这些结果表明，中等光度AGN的宿主星系在红移约为2时，与相似质量的非活跃星系相比，不太可能参与正在进行的合并或相互作用。AGN宿主中观察到的高盘状比例似乎与预测相矛盾，即在红移约为2时，即使是在中等X射线光度下，由合并驱动的吸积应是主导的AGN燃料模式。尽管我们不能排除小规模合并可能是这些系统的触发因素，但相对未受扰动的盘状宿主的大群体存在表明，在红移约为2时，恒定过程在为AGN活动提供燃料方面比之前认为的起着更重要的作用。 显示英文摘要

摘要： Using HST/WFC3 imaging taken as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), we examine the role that major galaxy mergers play in triggering active galactic nuclei (AGN) activity at z~2. Our sample consists of 72 moderate-luminosity (Lx ~ 1E42-1E44 erg/s) AGN at 1.5<z<2.5 that are selected using the 4 Msec Chandra observations in the Chandra Deep Field South, the deepest X-ray observations to date. Employing visual classifications, we have analyzed the rest-frame optical morphologies of the AGN host galaxies and compared them to a mass-matched control sample of 216 non-active galaxies at the same redshift. We find that most of the AGN reside in disk galaxies (51.4%), while a smaller percentage are found in spheroids (27.8%). Roughly 16.7% of the AGN hosts have highly disturbed morphologies and appear to be involved in a major merger or interaction, while most of the hosts (55.6%) appear relatively relaxed and undisturbed. These fractions are statistically consistent with the fraction of control galaxies that show similar morphological disturbances. These results suggest that the hosts of moderate-luminosity AGN are no more likely to be involved in an ongoing merger or interaction relative to non-active galaxies of similar mass at z~2. The high disk fraction observed among the AGN hosts also appears to be at odds with predictions that merger-driven accretion should be the dominant AGN fueling mode at z~2, even at moderate X-ray luminosities. Although we cannot rule out that minor mergers are responsible for triggering these systems, the presence of a large population of relatively undisturbed disk-like hosts suggests that secular processes play a greater role in fueling AGN activity at z~2 than previously thought.