星系并合会产生不同尺度距离的星系对甚至双活动星系核 , 同时在过程中会触发星暴以及超大质量黑洞的活动。 在光谱上, 当两个星系并合到kpc尺度时, 其两个核的相互绕转在总光谱上会表现出窄线双峰谱线轮廓。 以这个观测特性为起点, 从郭守敬望远镜巡天的第四次释放数据(LAMOST DR4)中系统的搜寻带有窄发射线双峰特征的双AGN候选体。 AGN的发射线光谱轮廓由发射线的若干种不同的动力学成分构成, 主要可以分为三类, 窄线成分(Hβ, [OⅢ], Hα and [NⅡ]), [OⅢ]的线翼、 以及宽的Balmer发射线。 基于LAMOST DR4河外光谱数据, 应用了一套搜寻流程, 在初始筛选(涉及到发射线的信噪比、 等值宽度和红移)及目视检查挑选之后, 通过建立的多高斯拟合模型挑选出在发射线的流量、 半高全宽、 窄线双峰之间速度分离程度等一系列参数上符合我们限制要求的样本, 并借助于Baldwin-Phillips-Terlevich (BPT) 图来鉴别每个成分的来源, 确定出了28个双AGN候选体。 为了获取更准确的星族成分并发现这类双AGN候选体样本的共有特性, 对28个双AGN候选体的光谱流量用一个低阶多项式重新进行了修正并采用传统的统一插值和中值方法对其进行合并得到一条高信噪比光谱, 并以目前已有的来源于LAMOST星系光谱数据的Ⅱ型AGN(单AGN)的复合光谱作为对照样本, 采用STARLIGHT软件分别拟合了合并的双AGN和对照的单AGN的光学光谱中的吸收线和连续谱。 通过研究它们的星族特性及两者间的异同, 发现与单AGN复合谱相比, 双AGN候选体样本的合并谱具有更多中等年龄及老年星族的贡献, 反映出更剧烈的中心黑洞。 在金属丰度方面, 单AGN的主导星族为太阳金属丰度的星族Z_☉, 而双AGN候选体合并谱中贡献较多的星族为亚太阳金属丰度星族0.2 Z_☉和富金属丰度星族2.5 Z_☉, 表现出了差异性特征, 也预示着这类样本中恒星形成历史更加复杂, 呈现出了多样化。 在幂律谱成分贡献方面在单、 双AGN中老年星族都贡献了其大部分质量, 但单AGN复合谱中幂律成分占比为8.2%, 明显高于双AGN候选体合并谱中幂律成分的贡献。

The merger of massive galaxies can also invoke a series of phenomena such as the starburst and SMBH activities, besides galaxies pairing and dual AGNs. When two galaxies merger to kiloparsec (kpc) scale and begin to co-rotate with each other, and the adjacent narrow line regions are sensed by a single spectrograph slit or fiber, double-peaked emission lines would appear in the integrated spectra. In this paper, starting from this observation characteristic, we systematically search for dual AGN candidates whose spectra display double-peaked narrow emission line features in the Data Release 4 of LAMOST survey (LAMOST DR4). The profiles of emission lines of AGN spectra are composed of several different dynamic components, which can be divided into three types including narrow line components (Hβ, [OⅢ], Hα and [NⅡ]), wings of [OⅢ] lines, and broad Balmer emission lines. Based on LAMOST DR4 extragalactic spectra, we apply a set of search process, after the initial screening (involving the signal-to-noise ratio, the equivalent width and redshift cuts) and visual check and selection, we establish a sample with double-peaked narrow emission lines, which meets with our criteria of fluxes, full-width-half-maximum and velocity gap between two narrow components in their multi-gaussians fitting. Based on the Baldwin-Phillips-Terlevich (BPT) diagnosis, we finally detect 28 dual AGN candidates. In order to obtain more accurate and find the common characteristics of this kind of dual AGN candidates, we re-correct the spectral flux of these 28 objects with a low-order polynomial and combine them with the traditional interpolation and median method to obtain a high signal-to-noise ratio spectrum. We also take a composite spectra constructed from single type Ⅱ AGNs in LAMOST DR4 as the control sample. The software STARLIGHT is carried out to fit these two spectra, and the contributions of stars of different ages and metallicities are quantified for more direct comprehension. We find that dual AGN candidates will host more contributions from the middle age and the old populations than the single AGN composite, indicating a more intense central black hole activity. As for the metallicity effects, the dominant stellar population of single AGN is the population with solar metallicity Z_☉, while the spectra from dual AGN candidates show a significant contribution from populations with metallicities 0.2 Z_☉ and 2.5 Z_☉, showing a heterogeneous feature and revealing a more complicated star formation history encodes in these possible dual AGNs than it exists in corresponding regular sample. A power-law is considered when we conduct the fitting, and the contributions of this featureless continuum component in single AGN account for 8.2%, which is significantly higher than that in the dual AGN candidates.