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arXiv 1503.08052astro-ph.COastro-ph.GA
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透镜运动和不均匀放大对图像光谱的影响

Effects of Lens Motion and Uneven Magnification on Image Spectra

Indranil Banik, Hongsheng Zhao

摘要:

与直觉相反,在任何度量引力理论中,一个被移动的星系团透镜化的扩展星系的图像应该有稍微不同的光谱。这主要有两个原因。一种是依赖于运动透镜的引力势随时间变化($\text{Moving}$ $\text{Cluster}$ $\text{Effect}$、$\text{MCE}$)。另一种是由于扩展的旋转源($\text{Differential}$ $\text{Magnification}$ $\text{Effect}$、$\text{DME}$)的放大率不均匀。由于宇宙膨胀,图像之间的时间延迟也会导致它们的红移不同。这种差异膨胀效应可能很小。使用一个简单的模型,我们从第一原理推导出这些效应。一个应用是子弹状星系团,它的大切向速度可能与$ΛCDM$范例不一致。这个速度可以用复杂的流体动力学模型来估计。使用MCE可以避免与这些模型的不一致。我们认为,MCE应该与ALMA观察。然而,如果使用典型的旋涡星系作为源,这样的测量可能会被DME破坏。幸运的是,我们发现,如果详细的谱线配置文件是可用的,然后DME和MCE可以区分。它也可能是可行的,以计算多少DME应该影响每个图像的平均红移。要准确地做到这一点,需要对源进行解析观测。DME的数量级是源的角尺寸除以爱因斯坦半径乘以源上的红移变化。因此,它主要影响在某些方向上的近边缘螺旋星系。这表明,观察者应该通过仔细选择目标来减少DME,我们将详细讨论这种可能性。

英文摘要:

Counter to intuition, the images of an extended galaxy lensed by a moving galaxy cluster should have slightly different spectra in any metric gravity theory. This is mainly for two reasons. One relies on the gravitational potential of a moving lens being time-dependent (the $\text{Moving}$ $\text{Cluster}$ $\text{Effect}$, $\text{MCE}$). The other is due to uneven magnification across the extended, rotating source (the $\text{Differential}$ $\text{Magnification}$ $\text{Effect}$, $\text{DME}$). The time delay between the images can also cause their redshifts to differ because of cosmological expansion. This Differential Expansion Effect is likely to be small. Using a simple model, we derive these effects from first principles. One application would be to the Bullet Cluster, whose large tangential velocity may be inconsistent with the $ΛCDM$ paradigm. This velocity can be estimated with complicated hydrodynamic models. Uncertainties with such models can be avoided using the MCE. We argue that the MCE should be observable with ALMA. However, such measurements can be corrupted by the DME if typical spiral galaxies are used as sources. Fortunately, we find that if detailed spectral line profiles were available, then the DME and MCE could be distinguished. It might also be feasible to calculate how much the DME should affect the mean redshift of each image. Resolved observations of the source would be required to do this accurately. The DME is of order the source angular size divided by the Einstein radius times the redshift variation across the source. Thus, it mostly affects nearly edge-on spiral galaxies in certain orientations. This suggests that observers should reduce the DME by careful choice of target, a possibility we discuss in some detail.

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