SkyFACT：使用自适应模板和惩罚似然度的gamma-ray发射的高维建模
SkyFACT: High-dimensional modeling of gamma-ray emission with adaptive templates and penalized likelihoods
摘要：
我们提出了SkyFACT（Sky Factorization with Adaptive Constrained Templates），这是一种研究、建模和分解弥散伽马射线辐射的新方法。像以前的大多数分析一样，这种方法依赖于宇宙射线传播代码（如GALPROP和DRAGON）的预测。然而，在以前的方法相比，我们占的事实，模型是不完美的，并允许一个非常大的数量（$\gtrsim10^5$）的滋扰参数参数，这些缺陷。我们结合图像重建和自适应空间-光谱模板回归的方法在一个相干的混合方法。为此，我们使用惩罚泊松似然回归，正则化函数的动机是最大熵方法。我们介绍的方法，有效地处理高维的凸优化问题，以及相关的半稀疏协方差矩阵，使用L-BFGS-B算法和Cholesky分解。我们测试的方法都在合成数据，以及从银河系内部，$|\ell|<90^\circ$和$|b|<20^\circ$，观测费米大天区望远镜的伽马射线发射。最后，我们定义了一个简单的参考模型，删除了大部分的残留排放的内部星系，根据传统的扩散排放组件以及组件的费米气泡，费米银河系中心过剩，并沿银河系盘扩展源。这个参考模型的变体可以作为未来研究银河系盘内外弥散辐射的基础。
英文摘要：
We present SkyFACT (Sky Factorization with Adaptive Constrained Templates), a new approach for studying, modeling and decomposing diffuse gamma-ray emission. Like most previous analyses, the approach relies on predictions from cosmic-ray propagation codes like GALPROP and DRAGON. However, in contrast to previous approaches, we account for the fact that models are not perfect and allow for a very large number ($\gtrsim10^5$) of nuisance parameters to parameterize these imperfections. We combine methods of image reconstruction and adaptive spatio-spectral template regression in one coherent hybrid approach. To this end, we use penalized Poisson likelihood regression, with regularization functions that are motivated by the maximum entropy method. We introduce methods to efficiently handle the high dimensionality of the convex optimization problem as well as the associated semi-sparse covariance matrix, using the L-BFGS-B algorithm and Cholesky factorization. We test the method both on synthetic data as well as on gamma-ray emission from the inner Galaxy, $|\ell|<90^\circ$ and $|b|<20^\circ$, as observed by the Fermi Large Area Telescope. We finally define a simple reference model that removes most of the residual emission from the inner Galaxy, based on conventional diffuse emission components as well as components for the Fermi bubbles, the Fermi Galactic center excess, and extended sources along the Galactic disk. Variants of this reference model can serve as basis for future studies of diffuse emission in and outside the Galactic disk.
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