On the orbits that generate the X-shape in the Milky Way bulge
On the orbits that generate the X-shape in the Milky Way bulge
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关于在银河系核球中生成X形的轨道
DOI：
10.1093/mnras/stx1262
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发表时间：
2017-03
影响因子：
4.8
通讯作者：
Debattista Victor P.
中科院分区：
文献类型：
--
作者：
Abbott Caleb G.;Valluri Monica;Shen Juntai;Debattista Victor P.
银河系（MW）凸起显示为方形/花生状或X形凸起本文研究了一个棒状盘星系的N体模型中的轨道，该模型被缩放以匹配MWbulge的运动学。我们生成了投影的恒星表面密度图，模糊的掩蔽图像，3D多余质量分布图，以及一个星系的轨道。（显示椭球外的质量），视线数计数分布，以及模拟的2D视线运动学以及共同添加的轨道族，以便识别主要负责BP/X形状的轨道。我们估计，在这个模型中的酒吧的质量的19%和23%之间与BP/X形状，大多数酒吧轨道有助于这种形状，这是清楚地看到在投影表面密度图和3D多余的质量为非共振箱轨道，“香蕉”轨道，“鱼/椒盐卷饼”轨道和“brezel”轨道。虽然只有后两个家庭（占总质量的7.5%）显示出明显的X形在unsharp掩蔽图像，我们发现，几乎所有的酒吧轨道家庭贡献一些质量的3D BP/X形。所有共同添加的轨道家庭显示出分歧的恒星数计数分布的距离，类似于在MW中观察到的分歧的红丛星。然而，只有箱形轨道家族显示出随着银河系纬度的增加，峰的分离度也在增加|B|，与观察到的相似。我们的分析表明，没有一个单一的轨道族可以完全解释与MW的BP/X形凸起相关的所有观察到的特征，但非共振盒和各种共振小盒轨道在距离中心不同的距离处共同贡献了这一特征。我们建议，由于盒轨道（这是在酒吧占主导地位的人口）有三个不可分割的轨道基本频率，他们的三维形状是高度灵活的，像李萨如图，这个家庭的轨道是最容易能够适应演变的形状的潜在的潜力。© 2017作者。
The Milky Way (MW) bulge shows a boxy/peanut or X-shaped bulge (hereafter BP/X) when viewed in infrared ormicrowave bands.We examine orbits in an N-body model of a barred disc galaxy that is scaled to match the kinematics of theMWbulge.We generate maps of projected stellar surface density, unsharp masked images, 3D excess-mass distributions (showing mass outside ellipsoids), line-of-sight number count distributions, and 2D line-of-sight kinematics for the simulation as well as co-added orbit families, in order to identify the orbits primarily responsible for the BP/X shape. We estimate that between 19 and 23 per cent of the mass of the bar in this model is associated with the BP/X shape and that the majority of bar orbits contribute to this shape that is clearly seen in projected surface density maps and 3D excess mass for non-resonant box orbits, 'banana' orbits, 'fish/pretzel' orbits and 'brezel' orbits. Although only the latter two families (comprising 7.5 per cent of the total mass) show a distinct X-shape in unsharp masked images, we find that nearly all bar orbit families contribute some mass to the 3D BP/X-shape. All co-added orbit families show a bifurcation in stellar number count distribution with distance that resembles the bifurcation observed in red clump stars in the MW. However, only the box orbit family shows an increasing separation of peaks with increasing galactic latitude |b|, similar to that observed. Our analysis suggests that no single orbit family fully explains all the observed features associated with the MW's BP/X-shaped bulge, but collectively the non-resonant boxes and various resonant boxlet orbits contribute at different distances from the centre to produce this feature. We propose that since box orbits (which are the dominant population in bars) have three incommensurable orbital fundamental frequencies, their 3D shapes are highly flexible and, like Lissajous figures, this family of orbits is most easily able to adapt to evolution in the shape of the underlying potential. © 2017 The Authors.
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