超越椭圆：用$Isofit$和$Cmodel$精确模拟半导体的等光结构
Beyond Ellipse(s): Accurately Modelling the Isophotal Structure of Galaxies with $Isofit$ and $Cmodel$
摘要：
这项工作介绍了一种新的拟合形式主义的等照度线，使更准确的建模的星系与非椭圆形的形状，如盘星系的边缘或星系与X形/花生凸起。在这个计划中，定义准椭圆等照度线的角度参数是从常用的，但不合适的，极坐标的“偏心异常”。这提供了对椭圆度偏差的更好描述，更好地捕捉真实的等照度线形状。此外，这使得有可能准确地恢复表面亮度轮廓，使用正确的方位平均等照度线，和任何星系的二维模型：迄今无处不在的，但人为的，交叉状的功能，在残留的图像被完全删除。该形式已在IRAF任务$Ellipse$和$Bmodel$中实施，以创建新任务“$Isofit$”和“$Cmodel$”。新的工具在这里演示应用到五个星系，选择有代表性的案例研究的几个领域，这种技术使人们有可能获得新的科学见解。具体而言：通过边缘星系中的四次谐波阶数正确量化盒状/盘状等照度线，量化X形/花生状凸起，用于模拟盘中棒的高阶傅立叶矩，以及复杂的等照度线形状。高阶（n > 4）谐波现在变得有意义，并且可以与结构性质相关，如已知的盒状/盘状。这项工作还说明了如何准确的建设，和减法，从星系图像的模型，有利于识别和恢复重叠的来源，如球状星团和光学对应的X射线源。
英文摘要：
This work introduces a new fitting formalism for isophotes which enables more accurate modelling of galaxies with non-elliptical shapes, such as disk galaxies viewed edge-on or galaxies with X-shaped/peanut bulges. Within this scheme, the angular parameter which defines quasi-elliptical isophotes is transformed from the commonly used, but inappropriate, polar co-ordinate to the `eccentric anomaly'. This provides a superior description of deviations from ellipticity, better capturing the true isophotal shape. Furthermore, this makes it possible to accurately recover both the surface brightness profile, using the correct azimuthally-averaged isophote, and the two-dimensional model of any galaxy: the hitherto ubiquitous, but artificial, cross-like features in residual images are completely removed. The formalism has been implemented into the IRAF tasks $Ellipse$ and $Bmodel$ to create the new tasks `$Isofit$', and `$Cmodel$'. The new tools are demonstrated here with application to five galaxies, chosen to be representative case-studies for several areas where this technique makes it possible to gain new scientific insight. Specifically: properly quantifying boxy/disky isophotes via the fourth harmonic order in edge-on galaxies, quantifying X-shaped/peanut bulges, higher-order Fourier moments for modelling bars in disks, and complex isophote shapes. Higher order (n > 4) harmonics now become meaningful and may correlate with structural properties, as boxyness/diskyness is known to do. This work also illustrates how the accurate construction, and subtraction, of a model from a galaxy image facilitates the identification and recovery of over-lapping sources such as globular clusters and the optical counterparts of X-ray sources.
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