| Strong emission lines in spectrum is the prominent observation feature of ac-tive galactic nuclei (AGNs). Using emission lines to study the physical properties of AGNs is the most widely used method, which provide numerous information to understand the nature of AGNs. Whether broad emission lines or narrow emis-sion lines, originated from ionization of gases by high-energy photons from center nuclear, can be used to infer AGNs properties. There are a variety of links be-tween the characteristics of the emission lines (such as flux intensity, equivalent width, and speed offset) and the various natures of AGNs. Many tremendous achievements in this field have been made. With the help of constantly updated observation equipment and approaches, using the emission lines to study the physical properties of AGNs become more deeper and more wider.This thesis mainly focused on the studies of some special astrophysical phe-nomena of AGNs, including the existence and the nature of dual AGNs, the rela-tionships between outflows of AGNs and nuclear activities, and the host galaxy evolution, by analysis of [O Ⅲ λλ4959,5007narrow emission lines. These are the latest progress in the formation and evolution of galaxies over the past decade. For dual AGNs, it has been found a considerable number of instances, and there are some large-scale survey for it. While outflow of AGNs, or feedback, has been considered to be an indispensable mechanism in AGNs activity and the evolution of the host galaxies. The paper is organized as follows:The first Chapter is a review of AGNs, including the standard model and the regions in which emission lines originated. We then describe the relationship between AGNs and their host galaxies in the hierarchical cosmological model, as well as the significance of our study. Furthermore, We briefly depict the complex structure of the [O Ⅲ] narrow emission line and its significance for AGN research, as well as the SDSS sky survey project.In Chapter2, we introduce a candidate for dual AGNs. We analyze the optical spectrum of type1QSO SDSS J1425+3231. After subtracting the contin-uum spectrum, its narrow emission lines such as [OⅢ] λλ4959,5007are double peaked. Then we carefully fit the double-peaked [OⅢ]lines using multiple Gaus-sian components. The black hole mass is estimated from the fitting parameters, and the origin of the double-peaked narrow emission lines is discussed. At last we suggest this QSO might be a dual AGN system. We also discuss the method and the possibility of finding dual AGNs.The third Chapter focuses on statistical studies of outflows in AGNs. We explore the asymmetric behavior of the narrow emission line [O Ⅲ] A5007in a type2AGNs sample with the blue shift narrow emission lines. It shows that there exists a strong correlation between the flux of core component and the wing. However, no correlation is found between the blueshift velocity of the broad wing and the host properties, such as Eddington ratio. We also compare the broad blueshift wing component in type1and type2AGNs. A higher blueshift velocity in type1AGNs sample indicates that the blueshift wing component is located nearer to the center of AGN. Finally, the broad blueshift wing of narrow emission line is suggested to be caused by the outflow of AGN, it is consistent with previous researches.Chapter four summarizes our works and presents ideas for future research. The prospect of a broadened application of our works has been proposed too. |
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