Bias from gas inhomogeneities in the pressure profiles as measured from X-ray and Sunyaev–Zeldovich observations
Bias from gas inhomogeneities in the pressure profiles as measured from X-ray and Sunyaev–Zeldovich observations
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根据 X 射线和 Sunyaev-Zeldovich 观测测量的压力剖面中气体不均匀性造成的偏差
DOI：
10.1093/mnras/stt224
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发表时间：
2012
影响因子：
4.8
通讯作者：
R. Sunyaev
中科院分区：
文献类型：
--
作者：
S. Khedekar;E. Churazov;A. Kravtsov;I. Zhuravleva;E. Lau;D. Nagai;R. Sunyaev
星系团的X射线观测提供了发射测量加权光谱，这些光谱是由星系团内介质（ICM）的密度和温度波动引起的。这是一个单一的温度等离子体发射模型，以提供气体密度和温度，这是敏感的气体不均匀性的估计。因此，X射线观测产生了热气体压力PX的潜在偏差估计。同时，Sunyaev-Zeldovich（SZ）观测直接测量积分气体压力PSZ。如果X射线压力分布相对于SZ有很强的偏差，那么人们就有可能探测气体的不均匀性（它们的振幅和物理性质），即使是在目前这一代望远镜无法分辨的尺度上。与此同时，一个弱的偏见的影响，可互换使用的质量代理，如YSZ和YX作为宇宙学探针。在本文中，我们研究了偏差（定义为bP（r）<$PX（r）/PSZ（r）−1）对ICM中涨落特性的依赖性，并考虑了温度和密度涨落之间的相关性。本文用多温等离子体发射模型对理想X射线与SZ观测中的不可约偏差作了简单的预测。我们还提供了一个简单的拟合形式来估计给定波动分布的偏差。在真实的观测中，由于仪器背景、光子统计量不足、非球面性、解投影方法等因素的影响，可能会产生额外的复杂情况。通过对流体动力学模拟中提取的16个团簇样本的分析，我们发现偏差的中值在R500范围内在±3%以内。在R500 < r < 1.5 R500时，它下降到−5%，然后在r & 2 R500时又上升到10%。单个弛豫簇之间的bP（r）的分散度很小-在R500内< 0.03的水平，但在r & 1.5 R500时变得显著更大（0.25）和高度偏斜（bP（r）<0）。对于我们发现的任何一个松弛的星系团|bP（r）|< 15%在R500内，在模拟中不同的输入物理实现中。非松弛团簇在bP（r）中表现出更大的分散（从半径到半径和从团簇到团簇）。
X-ray observations of galaxy clusters provide emission measure weighted spectra, arising from a range of density and temperature fluctuations in the intra-cluster medium (ICM). This is fitted to a single temperature plasma emission model to provide an estimate of the gas density and temperature, which are sensitive to the gas inhomogeneities. Therefore, X-ray observations yield a potentially biased estimate of the thermal gas pressure, PX. At the same time Sunyaev-Zeldovich (SZ) observations directly measure the integrated gas pressure, PSZ. If the X-ray pressure profiles are strongly biased with respect to the SZ, then one has the possibility to probe the gas inhomogeneities (their amplitude and physical nature), even at scales unresolved by the current generation of telescopes. At the same time, a weak bias has implications for the interchangeable use of mass proxies like YSZ and YX as cosmological probes. In this paper we investigate the dependence of the bias, defined as bP(r) ≡ PX(r)/PSZ(r)−1, on the characteristics of fluctuations in the ICM taking into account the correlation between temperature and density fluctuations. We made a simple prediction of the irreducible bias in idealised X-ray vs SZ observations using multi-temperature plasma emission model. We also provide a simple fitting form to estimate the bias given the distribution of fluctuations. In real observations there can be additional complications arising from instrumental background, insufficient photon statistics, asphericity, method of deprojection, etc. Analysing a sample of 16 clusters extracted from hydrodynamical simulations, we find that the median value of bias is within ±3% within R500, it decreases to −5% at R500 < r < 1.5 R500 and then rises back to ∼ 0% at r & 2 R500. The scatter of bP(r) between individual relaxed clusters is small – at the level of < 0.03 within R500, but turns significantly larger (0.25) and highly skewed (bP(r) ≫ 0) at r & 1.5 R500. For any relaxed cluster we find |bP(r)| < 15% within R500, across different implementations of input physics in the simulations. Unrelaxed clusters exhibit a larger scatter in bP(r) (both from radius to radius and from cluster to cluster).
簇内介质中气体团簇的性质和气体团簇因子
影响因子：
4.8
作者：
Eckert;Simionescu;Brüggen;Ettori
通讯作者：
Ettori