作者:J. S. Sanders、A. C. Fabian、S. W. Allen
DOI:10.1046/j.1365-8711.2000.03782.x
日期:2000.11
We present an analysis of X-ray colour maps of the cores of clusters of galaxies, formed from the ratios of counts in different X-ray bands. Our technique groups pixels lying between contours in an adaptively smoothed image of a cluster. We select the contour levels to minimize the uncertainties in the colour ratios, whilst preserving the structure of the object. We extend the work of Allen & Fabian by investigating the spatial distributions of cooling gas and absorbing material in cluster cores. Their sample is almost doubled: we analyse archive ROSAT Position Sensitive Proportional Counter (PSPC) data for 33 clusters from the sample of the 55 brightest X-ray clusters in the sky. Many of our clusters contain strong cooling flows. We present colour maps of a sample of the clusters, in addition to adaptively smoothed images in different bands. Most of the cooling flow clusters display little substructure, unlike several of the non-cooling-flow clusters.We fitted an isothermal plasma model with galactic absorption and constant metallicity to the mid-over-high energy colours in our clusters. Those clusters with known strong cooling flows have inner contours which fit a significantly lower temperature than the outer contours. Clusters in the sample without strong cooling flows show no significant temperature variation. The inclusion of a metallicity gradient alone was not sufficient to explain the observations. A cooling flow component plus a constant temperature phase did account for the colour profiles in clusters with known strong cooling flow components. We also had to increase the levels of absorbing material to fit the low-over-high colours at the cluster centres. Our results provide more evidence that cooling flows accumulate absorbing material. No evidence for increased absorption was found for the non-cooling-flow clusters.
我们对星系团核心的 X 射线颜色图进行了分析,这些颜色图是由不同 X 射线波段的计数比形成的。我们的技术将位于星系团自适应平滑图像中轮廓线之间的像素分组。我们选择等高线水平,以尽量减少颜色比的不确定性,同时保留天体的结构。我们对 Allen 和 Fabian 的工作进行了扩展,研究了星团核心中冷却气体和吸收物质的空间分布。他们的样本几乎增加了一倍:我们分析了天空中 55 个最亮 X 射线星团样本中 33 个星团的 ROSAT 位置敏感比例计数器(PSPC)存档数据。我们的许多星团都含有强烈的冷却流。除了不同波段的自适应平滑图像外,我们还展示了这些星团样本的彩色图。与几个非冷却流星团不同的是,大多数冷却流星团显示出很少的子结构。我们对星团的中高能量颜色拟合了一个具有银河系吸收和恒定金属性的等温等离子体模型。那些已知有强冷却流的星团,其内部轮廓拟合的温度明显低于外部轮廓。样本中没有强冷却流的星团则没有明显的温度变化。仅加入金属性梯度不足以解释观测结果。在已知有强冷却流成分的星团中,冷却流成分加上恒温阶段确实可以解释颜色剖面。我们还必须提高吸收物质的水平,以适应星团中心的低过高色彩。我们的结果提供了更多证据,证明冷却流积累了吸收物质。在非冷却流星团中没有发现吸收增加的证据。