绘制外部星系的非轴对称速度场
Mapping non-axisymmetric velocity fields of external galaxies
AI总结：
开发了基于普通最小二乘法的非轴对称模型拟合算法，通过环与弧段结合重建外部星系各向异性非圆运动，并应用于THINGS样本25个盘状星系生成二维速度图。
摘要：
盘状星系通常处于物质沿几乎闭合的圆轨道运动的稳定构型中。然而，由扭曲、翘曲、不对称或卫星相互作用引起的非圆运动很普遍，并在星系速度图上留下独特特征。我们开发了一种算法，使用普通最小二乘法将非轴对称模型拟合到外部星系观测到的二维视线速度图上，该算法允许各向异性的非圆运动。该方法将星系近似为平坦圆盘，这对于光学半径内翘曲罕见的旋涡星系是一个合理的假设。在可能延伸至翘曲区域的HI分布外围，我们将该方法与标准的旋转倾斜环模型结合，以保守地约束平坦圆盘假设可被认为有效的半径范围。在此范围内，环内平均的横向和径向速度剖面可直接从速度图重建。该算法的创新之处在于除环之外还使用弧段：这样可以在两个分量中测量空间速度各向异性，从而重建角分辨的粗粒化二维速度图。我们将该算法应用于THINGS样本中的25个盘状星系，为其提供了两个速度分量的2D图。
英文摘要：
Disk galaxies are typically in a stable configuration where matter moves in almost closed circular orbits. However, non-circular motions caused by distortions, warps, lopsidedness, or satellite interactions are common and leave distinct signatures on galaxy velocity maps. We develop an algorithm that uses an ordinary least square method for fitting a non-axisymmetric model to the observed two-dimensional line-of-sight velocity map of an external galaxy, which allows for anisotropic non-circular motions. The method approximates a galaxy as a flat disk, which is an appropriate assumption for spiral galaxies within the optical radius where warps are rare. In the outer parts of HI distributions, which may extend well into the warp region, we use this method in combination with a standard rotating tilted ring model to constrain the range of radii where the flat disk assumption can be conservatively considered valid. Within this range, the transversal and radial velocity profiles, averaged in rings, can be directly reconstructed from the velocity map. The novelty of the algorithm consists in using arc segments in addition to rings: in this way spatial velocity anisotropies can be measured in both components, allowing for the reconstruction of angularly resolved coarse-grained two-dimensional velocity maps. We applied this algorithm to 25 disk galaxies from the THINGS sample for which we can provide 2D maps of both velocity components.
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