大型早型星系，包含橢圓與透鏡星系，主要來源於星系的合併。因此大型早型星系的許多性質都與合併星系的過程有關，例如星系的外形與暗物質分佈。本論文研究不同環境下的早型星系的形狀，發現相對而言在高密度區的早型星系要比低密度區的早型星系接近球對稱。一個可能的原因是兩者在星系合併前的空間分佈不同，或是高密度區的早型星系受到周圍星系的潮汐力的影響而變圓。另外，透過比較早型星系與螺旋星系的動力學質量分佈得知，早型星系的暗物質比例至少與螺旋星系相當，且早型星系的衛星星系有較橢的繞行軌道。我們推測是因為在星系合併過程中合併星系的角動量會傳遞給其衛星星系而讓其有較橢的軌道。;Large early-type galaxies (ETGs), including elliptical and lenticular galaxies, are mainly formed from major mergers of galaxies. Therefore, some of the properties of large ETGs would be related to the process of merging galaxies, such as the shapes of galaxies and the distribution of dark matter. This thesis studies the shapes of ETGs in different environments. The results show that the ETGs in higher density environments are relatively closed to spherically symmetric than those in lower density environments. One possible reason is that the spatial distributions of the progenitor galaxies of the mergers are different, or the ETGs in the high-density environments become rounder due to the tidal force of the surrounding galaxies. Furthermore, the results of comparing the dynamical mass distributions of ETGs with those of spiral galaxies show that the dark matter fraction of ETGs should be at least equivalent to that of spiral galaxies and that the orbital shapes of satellite galaxies of ETGs should be relatively elliptical than those of spiral galaxies. One possible reason is that the angular momentum of the merging galaxies will be transferred to their satellite galaxies during the merging process, causing the orbital shapes relatively elliptical.
