标题： 形态不对称性与低红移星系核活动之间的关系 显示英文标题

标题： The Relation between Morphological Asymmetry and Nuclear Activity in Low-redshift Galaxies

摘要： 星系的形态反映了它们的形成历史以及环境带来的持续动力扰动。 分析来自Pan-STARRS1巡天的i波段图像，我们研究了一个大而定义明确的附近活动星系核（AGN）样本的宿主星系的光学形态不对称性，以探讨合并和相互作用在触发核活动中的作用。 这些AGN包括245个类型1和4514个类型2天体，与4537个在红移和恒星质量上匹配的恒星形成星系进行比较。 我们开发了一种全面的掩码策略，以隔离目标天体的发射，同时排除前景恒星和其他污染源，同时保留亮度相近的投影伴星，这些伴星可能是主要的合并体。 在三种非参数指标中，流行的CAS不对称参数和外层不对称参数（A_outer）对于恒星形成星系和类型2 AGN都能提供稳健的形态扭曲度量，而只有A_outer对类型1 AGN有效。 相比之下，形状不对称性更容易受到背景噪声的影响。 不对称指数>0.4能有效追踪可能正在进行合并的系统。 与理论预期相反，星系相互作用和合并并不是核活动的主要驱动因素，至少在我们研究的低红移、相对低光度的AGN样本中不是这样，其宿主星系的不对称性明显低于恒星形成星系的对照样本。 此外，类型2 AGN在形态上与它们的类型1对应物无法区分。 AGN活动水平与不对称性之间没有相关性，甚至在主要合并候选者中也没有。 作为副产品，我们发现，与之前的研究一致，恒星形成星系的平均不对称性在主序列之上增加，尽管并非所有主要合并都表现出增强的恒星形成。 显示英文摘要

摘要： The morphology of galaxies reflects their assembly history and ongoing dynamical perturbations from the environment. Analyzing i-band images from the Pan-STARRS1 Survey, we study the optical morphological asymmetry of the host galaxies of a large, well-defined sample of nearby active galactic nuclei (AGNs) to investigate the role of mergers and interactions in triggering nuclear activity. The AGNs, comprising 245 type 1 and 4514 type 2 objects, are compared with 4537 star-forming galaxies matched in redshift and stellar mass. We develop a comprehensive masking strategy to isolate the emission of the target from foreground stars and other contaminating sources, all the while retaining projected companions of comparable brightness that may be major mergers. Among three variants of nonparametric indices, both the popular CAS asymmetry parameter and the outer asymmetry parameter (A_outer) yield robust measures of morphological distortion for star-forming galaxies and type 2 AGNs, while only A_outer is effective for type 1 AGNs. The shape asymmetry, by comparison, is affected more adversely by background noise. Asymmetry indices > 0.4 effectively trace systems that are candidate ongoing mergers. Contrary to theoretical expectations, galaxy interactions and mergers are not the main drivers of nuclear activity, at least not in our sample of low-redshift, relatively low-luminosity AGNs, whose host galaxies are significantly less asymmetric than the control sample of star-forming galaxies. Moreover, type 2 AGNs are morphologically indistinguishable from their type 1 counterparts. The level of AGN activity does not correlate with asymmetry, not even among the major merger candidates. As a by-product, we find, consistent with previous studies, that the average asymmetry of star-forming galaxies increases above the main sequence, although not all major mergers exhibit enhanced star formation.