直杆观测特性的反投影不变性
Uncertainties in the Deprojection of the Observed Bar Properties
摘要：
在观测中，重要的是将表征棒的两个基本量进行反投影，即，它的长度（$a$）和椭圆率（$e$），在任何仔细的分析之前，面对的价值观。然而，目前对常用的解投影方法的不确定度还缺乏系统的估计。模拟星系非常适合这项研究。我们将两个模拟棒星系投影到一个具有不同棒取向和盘倾角（$i$）的二维平面上。棒的性能测量和反投影与流行的反投影方法在文献中。一般来说，解投影不确定度随着$i$的增加而增加。当$i$大于$60^\circ$时，由于杆的垂直厚度，所有的解投影方法都表现得很差。因此，未来棒星系的统计研究应该排除比$60^\circ$更倾斜的星系。在中等倾斜角（$i\leq60^\circ$），2D解投影方法（分析和图像拉伸）和基于傅立叶的方法（傅立叶分解和杆间对比度）在杆长度和椭圆度的不确定性$\sim10\%$的情况下表现得相当好。而在某些极端情况下，一维解析解投影的不确定度可高达$100\%$。我们发现，不同的酒吧测量方法显示出系统的差异，在解投影的不确定性。我们进一步讨论了去投影不确定性因素，重点是最重要的一个，即，酒吧本身的3D结构。我们构建了两个三轴玩具酒吧模型，可以定性地再现的1D和2D分析deprojunctions的结果，他们确认，酒吧的垂直厚度是不确定性的主要来源。
英文摘要：
In observations, it is important to deproject the two fundamental quantities characterizing a bar, i.e., its length ($a$) and ellipticity ($e$), to face-on values before any careful analyses. However, systematic estimation on the uncertainties of the commonly used deprojection methods is still lacking. Simulated galaxies are well suited in this study. We project two simulated barred galaxies onto a 2D plane with different bar orientations and disk inclination angles ($i$). Bar properties are measured and deprojected with the popular deprojection methods in the literature. Generally speaking, deprojection uncertainties increase with increasing $i$. All the deprojection methods behave badly when $i$ is larger than $60^\circ$, due to vertical thickness of the bar. Thus, future statistical studies of barred galaxies should exclude galaxies more inclined than $60^\circ$. At moderate inclination angles ($i\leq60^\circ$), 2D deprojection methods (analytical and image stretching) and Fourier-based methods (Fourier decomposition and bar-interbar contrast) perform reasonably well with uncertainties $\sim10\%$ in both the bar length and ellipticity. Whereas the uncertainties of the 1D analytical deprojection can be as high as $100\%$ in certain extreme case. We find that different bar measurement methods show systematic differences in the deprojection uncertainties. We further discuss the deprojection uncertainty factors with the emphasis on the most important one, i.e., the 3D structure of the bar itself. We construct two triaxial toy bar models that can qualitatively reproduce the results of the 1D and 2D analytical deprojections; they confirm that the vertical thickness of the bar is the main source of uncertainties.
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