用{ \sl Chandra} CCD谱搜索ICM中的体运动的方法：对Bullet团簇的应用
A method to search for bulk motions in the ICM with {\sl Chandra} CCD spectra: application to the Bullet cluster
摘要：
本文提出了一种基于{ \sl Chandra} CCD数据在合并星系团的团内介质（ICM）中搜索体运动的策略。我们的目标是从$K_α$线发射的质心得到的ICM投影区域的平均红移的鲁棒测量。我们深入探讨了视线方向上未知温度结构的影响，以准确评估系统不确定性对ICM红移的影响。我们把我们的方法应用到“子弹星系团”（1 E ~0657-56）。我们直接确定23个独立的区域的表面亮度轮廓的基础上，并测量的红移平均沿视线在每个ICM。我们发现，在这些地区的红移分布是轻微的不一致的零假设，一个恒定的红移或没有散装运动的ICM，在约$2\, σ$的置信水平。我们尝试性地确定了最可能受整体运动影响的区域，并发现沿视线的最大速度梯度约为$(46\pm 13)$ $\rm km~s^{-1}~kpc^{-1}$，沿“子弹”路径的尺度为$\sim 260 $ kpc。“我们将其解释为一个重要的ICM质量沿着垂直于合并的方向被推开的可能特征。这一初步结果是有希望的系统搜索的基础上空间分辨光谱分析的{ \sl钱德拉} CCD数据的明亮，中等红移星系团的整体运动。这一初步结果是有希望的系统搜索的基础上空间分辨光谱分析的{ \sl钱德拉} CCD数据的明亮，中等红移星系团的整体运动。
英文摘要：
We propose a strategy to search for bulk motions in the intracluster medium (ICM) of merging clusters based on {\sl Chandra} CCD data. Our goal is to derive robust measurements of the average redshift of projected ICM regions obtained from the centroid of the $K_α$ line emission. We thoroughly explore the effect of the unknown temperature structure along the line of sight to accurately evaluate the systematic uncertainties on the ICM redshift. We apply our method to the "Bullet cluster" (1E~0657-56). We directly identify 23 independent regions on the basis of the surface brightness contours, and measure the redshift of the ICM averaged along the line of sight in each. We find that the redshift distribution across these regions is marginally inconsistent with the null hypothesis of a constant redshift or no bulk motion in the ICM, at a confidence level of about $2\, σ$. We tentatively identify the regions most likely affected by bulk motions and find a maximum velocity gradient of about $(46\pm 13)$ $\rm km~s^{-1}~kpc^{-1}$ along the line of sight on a scale of $\sim 260 $ kpc along the path of the "bullet." We interpret this as the possible signature of a significant mass of ICM pushed away along a direction perpendicular to the merging. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of {\sl Chandra} CCD data. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of {\sl Chandra} CCD data.
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