THE SPATIAL DISTRIBUTIONS OF COOLING GAS AND INTRINSIC X-RAY-ABSORBING MATERIAL IN COOLING FLOWS
THE SPATIAL DISTRIBUTIONS OF COOLING GAS AND INTRINSIC X-RAY-ABSORBING MATERIAL IN COOLING FLOWS
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冷却流中冷却气体和本征X射线吸收材料的空间分布
DOI：
10.1093/mnras/286.3.583
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发表时间：
1996
影响因子：
4.8
通讯作者：
A. Fabian
中科院分区：
文献类型：
--
作者：
S. Allen;A. Fabian
我们给出了用位置灵敏正比计数器(PSPC)在ROSAT上观测到的一个邻近X射线明亮冷却流团中冷却气体和本征X射线吸收物质的空间分布的研究结果。我们的分析方法使用了X射线颜色分布，它由选定能带中团簇的表面亮度分布的比率形成，以及Fabian等人的去投影代码的改编版本。我们发现，在我们的样本中，所有冷却流团都显示出显著的冷却气体中心浓度。在较大半径时，团簇呈现近似等温状态。详细地说，冷却材料的空间分布和发射率与去投影程序的预测很好地吻合，可以用来约束冷却流动的年龄。X射线颜色分布还表明星系团中有大量的本征X射线吸收。本征吸收随半径的减小而增大，且局限于冷却流所占据的区域。我们探索了吸收气体的一系列可能的空间分布，并讨论了从X射线数据测量柱密度所涉及的复杂性。我们表明，应用简单的光谱模型，其中本征吸收体被视为统一的前景屏幕，自然会导致对真实吸收量的严重低估。将我们的结果与之前用爱因斯坦天文台固态光谱仪进行的观测结果进行了比较，结果显示出合理的一致性，但要求吸收材料只覆盖部分X射线发射区。在吸收物质中太阳金属丰度假设下计算的团簇中心(30弧秒半径)区域的吸收气体质量可以通过冷却流动在几个108年的时间尺度上累积，这比流动的年龄要小得多。这意味着，在这些区域的冷却流中沉积的大部分物质不能留在吸收X射线的气体中。本文的结果为星系团中非均匀冷却流动的标准模型提供了有力的支持。
We present the results from a study of the spatial distributions of cooling gas and intrinsic X-ray-absorbing material in a sample of nearby, X-ray-bright cooling flow clusters observed with the Position Sensitive Proportional Counter (PSPC) on ROSAT. Our method of analysis employs X-ray colour profiles, formed from ratios of the surface brightness profiles of the clusters in selected energy bands, and an adapted version of the deprojection code of Fabian et al. We show that all of the cooling flow clusters in our sample exhibit significant central concentrations of cooling gas. At larger radii the clusters appear approximately isothermal. In detail, the spatial distributions and emissivity of the cooling material are shown to be in excellent agreement with the predictions from the deprojection code, and can be used to constrain the ages of the cooling flows. The X-ray colour profiles also indicate substantial levels of intrinsic X-ray absorption in the clusters. The intrinsic absorption increases with decreasing radius, and is confined to the regions occupied by the cooling flows. We explore a range of likely spatial distributions for the absorbing gas and discuss the complexities involved in the measurement of column densities from X-ray data. We show that the application of simple spectral models, in which the intrinsic absorber is treated as a uniform foreground screen, will naturally lead to significant underestimates of the true amounts of absorption. Comparison of our results with previously reported observations made with the Einstein Observatory Solid State Spectrometer shows reasonable agreement, but requires that the absorbing material only partially covers the X-ray-emitting regions. The mass of absorbing gas in the central (30 arcsec radius) regions of the clusters calculated under the assumption of solar metallicity in the absorbing material can be accumulated by the cooling flows on time scales of a few 108 yr, which are much less than the ages of the flows. This implies that most of the material deposited by the cooling flows in these regions cannot remain in X-ray-absorbing gas. The results presented in this paper provide strong support for the standard model of inhomogeneous cooling flows in clusters of galaxies.