Lensing Properties of Cored Galaxy Models
Lensing Properties of Cored Galaxy Models
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核心星系模型的透镜特性
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发表时间：
2002
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通讯作者：
Ññññ Óùòò
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作者：
Aeº Ϻ;Úò;Ðððôøøø Ööööù׸»´¾ · Ü ¾ · Ý ¾ Õ ¾ Μ ¬¬ ¾ ¸ Øøø Òùñö;Ó Úú×××ðð;Ññññ Óùòò
发展了一种方法来评估类似同心椭圆上具有透镜势的星系图像的放大率。在四胞胎系统中，有两个偶数奇偶图像和两个奇数奇偶图像，以及一个消磁的、通常缺失的中心图像。给出了一种简单的轮廓积分，使偶奇偶像或奇偶像或中心像的放大倍数之和可以单独计算，而不需要显式解透镜方程。我们发现，图像对的和通常随源的位置而变化很大，而在没有裸露尖点的情况下，两对图像的符号和在切向焦散线内可以非常均匀。对于透镜势是椭圆半径的幂定律ψ∝(a2+x2+y2q-2)β/2的一族模型，得到了可见像的数目是平坦化q、外剪切γ和核半径a的函数。中心像的放大依赖于核的大小和引力势的斜率β。对于典型的光源和透镜红移，丢失的中心图像会导致很强的约束；斜率β必须是≲1，核心半径a必须是≲300pC。透镜星系群中的质量分布必须接近于尖点，尖点必须是等温的或更强的。这与附近大质量早期星系的高分辨率测光中看到的尖顶核心非常一致，这些星系通常在几百秒的破裂半径之外具有0.7%的β≈(或表面密度下降为-1.3%的距离)。Cuspy核心本身可以为缺失的中心图像提供解释。大半径的暗物质可能会改变投影密度的斜率；然而，如果斜率保持等温或更陡峭，而破裂半径仍然很小，那么中心图像仍然不可见。无线电地图的灵敏度必须提高50倍才能找到丰富的中心图像。
A method is developed to evaluate the magnifications of the images of galaxies with lensing potentials stratified on similar concentric ellipses. In a quadruplet system, there are two even-parity images and two odd-parity images, together with a demagnified and usually missing central image. A simple contour integral is provided which enables the sums of the magnifications of the even-parity or the odd-parity images or the central image to be separately calculated without explicit solution of the lens equation. We find that the sums for pairs of images generally vary considerably with the position of the source, while the signed sums of the two pairs can be remarkably uniform inside the tangential caustic in the absence of naked cusps. For a family of models in which the lensing potential is a power law of the elliptic radius, ψ ∝ (a2 + x2 + y2q-2)β/2, the number of visible images is found as a function of flattening q, external shear γ, and core radius a. The magnification of the central image depends on the size of the core and the slope β of the gravitational potential. It grows strongly with the source offset if β > 1, but weakly if β < 1. For typical source and lens redshifts, the missing central image leads to strong constraints; the slope β must be ≲1 and the core radius a must be ≲300 pc. The mass distribution in the lensing galaxy population must be nearly cusped, and the cusp must be isothermal or stronger. This is in good accord with the cuspy cores seen in high-resolution photometry of nearby, massive, early-type galaxies, which typically have β ≈ 0.7 (or surface density falling as distance-1.3) outside a break radius of a few hundred parsecs. Cuspy cores by themselves can provide the explanation of the missing central images. Dark matter at large radii may alter the slope of the projected density; however, provided the slope remains isothermal or steeper and the break radius remains small, then the central image remains unobservable. The sensitivity of the radio maps must be increased fifty-fold to find the central images in abundance.