杂色星系团气体含量：平均分数、散射、选择效应和与X射线光度的协方差
Variegate galaxy cluster gas content: Mean fraction, scatter, selection effects and covariance with X-ray luminosity
摘要：
我们使用一个独立于星团内介质含量的具有可靠质量的星团样本来测量平均气体质量分数及其散射、X射线选择对气体质量分数的偏差以及X射线光度与气体质量之间的协方差。该样本是由附近（$0.050<z<0.135$）宇宙中的34个星系团组成的，大部分是$14<\log M_{500}/M_\odot \lesssim 14.5$，质量是用焦散技术计算的。首先，我们发现，集成的气体密度分布有类似的形状，扩展早期的结果的基础上的子群的集群，如那些放松或X射线明亮的质量。其次，我们的样本的X射线无偏选择使我们能够揭示一个多样化的集群人口;气体质量分数显示$0.17\pm0.04$指数的分散，可能表明从集群到集群的反馈量相当可变，这比以前的样本中发现的更大，目标是星系团的亚群，如放松或X射线明亮的集群。的气体密度分布的相似性诱导X射线光度，气体质量和晕质量之间的几乎无散射的关系，并调制选择效应的晕气体质量分数：富含气体的集群优先包括在X射线选定的样品。几乎无散射关系也固定了$L_X-M$和$M_{gas}-M$关系的相对散射和斜率，并使核心切除的X射线光度和气体质量完全协变。因此，涉及X射线或SZ选定样品的宇宙学或天体物理学研究需要考虑选择效应和所研究的量与X射线光度/SZ强度的协方差。
英文摘要：
We use a cluster sample selected independently of the intracluster medium content with reliable masses to measure the mean gas mass fraction and its scatter, the biases of the X-ray selection on gas mass fraction, and the covariance between the X-ray luminosity and gas mass. The sample is formed by 34 galaxy clusters in the nearby ($0.050<z<0.135$) Universe, mostly with $14<\log M_{500}/M_\odot \lesssim 14.5$, and with masses calculated with the caustic technique. First, we found that integrated gas density profiles have similar shapes, extending earlier results based on subpopulations of clusters such as those that are relaxed or X-ray bright for their mass. Second, the X-ray unbiased selection of our sample allows us to unveil a variegate population of clusters; the gas mass fraction shows a scatter of $0.17\pm0.04$ dex, possibly indicating a quite variable amount of feedback from cluster to cluster, which is larger than is found in previous samples targeting subpopulations of galaxy clusters, such as relaxed or X-ray bright clusters. The similarity of the gas density profiles induces an almost scatterless relation between X-ray luminosity, gas mass, and halo mass, and modulates selection effects in the halo gas mass fraction: gas-rich clusters are preferentially included in X-ray selected samples. The almost scatterless relation also fixes the relative scatters and slopes of the $L_X-M$ and $M_{gas}-M$ relations and makes core-excised X-ray luminosities and gas masses fully covariant. Therefore, cosmological or astrophysical studies involving X-ray or SZ selected samples need to account for both selection effects and covariance of the studied quantities with X-ray luminosity/SZ strength.
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