是什么决定了边缘星系中X形结构的平坦性
What determines the flatness of X-shaped structures in edge-on galaxies
摘要：
最近对X形结构的观测研究表明，它们的张角值在一个很窄的范围内：从20度到43度，较小的X形结构似乎遵循一个特征张角~ 27度-31度。我们使用自洽的数值模拟来揭示什么参数的宿主星系管理的张开角蔓延。我们构建了一系列具有高空间分辨率的星系平衡模型，改变了暗晕和隆起在整体引力势中的贡献，模型的初始盘厚度和Toomre参数Q，并跟踪了近8 Gyrs的演化。每个模型都证明了具有不同平坦度的清晰X结构的形成。我们已经得到，在整个演化过程中，张开角在25度至42度的范围内。这些数值与观测数据大致一致。张角的最大变化是通过改变暗晕的质量来获得的。盘的初始厚度和Toomre参数是负责较小的变化的角度和较短的X-结构。这两个参数的增加改变了平面内酒吧和X-结构的形态。在某些情况下，我们甚至观察到双X结构。隆起的主要作用是防止在盘演化的中期和后期阶段发生屈曲。具有不同晕质量的模型的比较表明，可观察到的最小值的开口角可以与存在一个沉重的黑暗晕（超过3质量的光盘内的光学半径）。
英文摘要：
Recent observational studies of X-shaped structures revealed that values of their opening angles lie in a narrow range: from 20 deg to 43 deg with smaller X-shaped structures appearing to follow a characteristic opening angle ~ 27 deg - 31 deg. We use self-consistent numerical simulations to uncover what parameters of host galaxies govern the opening angle spread. We constructed a series of equilibrium models of galaxies with high spatial resolution, varying the dark halo and bulge contribution in the overall gravitational potential, the initial disc thickness of models and the Toomre parameter Q and followed their evolution for almost 8 Gyrs. Each model demonstrated the formation of clear X-structures with different flatness. We have obtained that opening angles lie in the range from 25 deg to 42 deg throughout the entire evolution. These values are roughly consistent with observational data. The greatest variation in the opening angles is obtained by varying the mass of the dark halo. The initial thickness of the disc and the Toomre parameter are responsible for smaller variations of the angle and shorter X-structures. An increase of both parameters changes the morphology of in-plane bars and X-structures. In some cases we observed even double X-structures. The main effect of the bulge is to prevent buckling at intermediate and late stages of the disc evolution. Comparison of models with different halo masses indicates that the smallest observable values of opening angles can be associated with the presence of a heavy dark halo (more than 3 masses of the disc within the optical radius).
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