arXiv 0708.37372007-08-28astro-ph

星系团的Sunyaev-Zeldovich和X射线图像的联合解投影

Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters

S. Ameglio, S. Borgani, E. Pierpaoli, K. Dolag

备注：: 17 pages, 15 figures, accepted by MNRAS
DOI：: 10.1111/j.1365-2966.2007.12384.x

摘要：

我们提出了两个非参数的反投影方法，旨在恢复三维的密度和温度分布的星系团从空间分辨的热Sunyaev-Zeldovich（tSZ）和X射线表面亮度图，从而避免使用X射线光谱数据。在这两种方法中，集群被假定为球对称的，并与洋葱皮结构建模。第一种方法遵循直接的几何方法。第二种方法是基于最大化的一个单一的联合（tSZ和X射线）的似然函数，它允许一个同时适合两个信号通过以下的蒙特卡洛马尔可夫链方法。这些技术进行了测试对一组宇宙学模拟集群，有和没有仪器噪声。我们沿着惯性动量张量主轴定义的三个正交方向投影每个簇。这使我们能够检查与沿着视线的簇伸长相关的去投影中的任何偏差。在对所有三个投影方向进行平均后，我们发现整体重建效果良好，对气体密度分布的高估较小（<~ 10%）。这变成了一个相当高估的维里半径内的气体质量，我们归因于残余气体结块的存在。除了这个小的偏差，重建有一个内在的散射约5%，这是由气体团块为主。沿着视线的簇伸长使分解的温度分布在r<~0.2r_vir处向上偏置并且在较大半径处向下偏置。一个类似的偏见也被发现在deprojected温度分布。总的来说，这变成了对气体质量的系统性低估，高达10%。（节录）

英文摘要：

We present two non-parametric deprojection methods aimed at recovering the three-dimensional density and temperature profiles of galaxy clusters from spatially resolved thermal Sunyaev-Zeldovich (tSZ) and X-ray surface brightness maps, thus avoiding the use of X-ray spectroscopic data. In both methods, clusters are assumed to be spherically symmetric and modeled with an onion-skin structure. The first method follows a direct geometrical approach. The second method is based on the maximization of a single joint (tSZ and X-ray) likelihood function, which allows one to fit simultaneously the two signals by following a Monte Carlo Markov Chain approach. These techniques are tested against a set of cosmological simulations of clusters, with and without instrumental noise. We project each cluster along the three orthogonal directions defined by the principal axes of the momentum of inertia tensor. This enables us to check any bias in the deprojection associated to the cluster elongation along the line of sight. After averaging over all the three projection directions, we find an overall good reconstruction, with a small (<~10 per cent) overestimate of the gas density profile. This turns into a comparable overestimate of the gas mass within the virial radius, which we ascribe to the presence of residual gas clumping. Apart from this small bias the reconstruction has an intrinsic scatter of about 5 per cent, which is dominated by gas clumpiness. Cluster elongation along the line of sight biases the deprojected temperature profile upwards at r<~0.2r_vir and downwards at larger radii. A comparable bias is also found in the deprojected temperature profile. Overall, this turns into a systematic underestimate of the gas mass, up to 10 percent. (Abridged)

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