Hot gas in the cold dark matter scenario: X-ray clusters from a high-resolution numerical simulation
Hot gas in the cold dark matter scenario: X-ray clusters from a high-resolution numerical simulation
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冷暗物质场景中的热气体：来自高分辨率数值模拟的 X 射线簇
DOI：
10.1086/174213
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
D. Ryu
中科院分区：
文献类型：
--
作者：
Hyesung Kang;R. Cen;J. Ostriker;D. Ryu
一种新的三维激波捕捉流体动力学程序被用来确定热气体在标准冷暗物质(CDM)宇宙模型中的分布。假设周期边界条件：在270(Exp 3)=10(exp 7.3)个单元的模拟中，跟随具有单元大小为0.31h(exp-1)mpc的85h(exp-1)MPC的盒子。采用由COBE和轻元素核合成确定的标准参数，sigma(Sub8)=1.05，omega(Subb)=0.06，假定h=0.5，我们找到了X射线发射团簇，并计算了几个波长的光度函数、温度分布和估计的尺寸，以及这些量的红移演化。我们发现，在我们的盒子中，大多数总的X射线发射率起源于相对较少的可识别星团，它们占据了盒子体积的大约10(exp-3)。这个标准的清洁发展机制模型，归一化到COBE，从L(子x)大于10(Exp 43)ergs/S的星团产生大约5倍多的排放，这并不是一个意想不到的结果。如果所有其他参数都保持不变，我们预计西格玛(小于8)=0.6会有足够的一致性。这为8h(exp-1)MPC尺度下比标准CDM更低的小尺度功率提供了一个新的、独立的论据。在这个模型中，由于星团而产生的1keV的背景辐射场大约是观测背景的三分之一，在经过数值效应校正后，这再次表明发射增加了大约5倍，Sigma(Sub8)的适宜性=0.6。如果我们使用观测到的星系团中气体与总质量的比率，而不是以轻元素核合成为基础的平均密度，那么每个星系团的计算光度将进一步增加约10倍。星系团的数密度增加到z约为1，但每个典型星系团的光度下降，结果是明亮星系团的数密度在这个红移范围内的演化是适度的，在z=0.7附近显示出一个宽峰，然后在红移z=3以上迅速下降。详细计算了不同能带L(子x)=10(Exp 40)-10(Exp 44)ergs/S的光度函数，并与ROSAT和其他观测数据进行了比较。发现的定量结果与其他使用半分析技术的研究人员发现的结果明显不一致。我们发现核心半径对星团光度的依赖很小，温度对光度的依赖关系由logKT(Subx)=A+B logL(Subx)给出，它比观测结果略陡(B=0.38)。正如预期的那样，计算的温度略高于观测温度，因为COBE归一化的清洁发展机制在相关尺度上具有太大的威力。发现了一个温和的平均温度梯度，在0.4h(exp-1)MPC时温度下降到中心值的90%，在0.9h(exp-1)MPC时温度下降到中心值的70%。检验归一化到欧米茄(B次)h(Exp 2)=0.015的星系团中气体与总质量的比率，并与观测结果相比较，我们得出结论，与White(1991年)一致，星系团观测证明了一个开放的宇宙。
A new, three-dimensional, shock-capturing hydrodynamic code is utilized to determine the distribution of hot gas in a standard cold dark matter (CDM) model of the universe. Periodic boundary conditions are assumed: a box with size 85 h(exp -1) Mpc having cell size 0.31 h(exp -1) Mpc is followed in a simulation with 270(exp 3) = 10(exp 7.3) cells. Adopting standard parameters determined from COBE and light-element nucleosynthesis, sigma(sub 8) = 1.05, omega(sub b) = 0.06, and assuming h = 0.5, we find the X-ray-emitting clusters and compute the luminosity function at several wavelengths, the temperature distribution, and estimated sizes, as well as the evolution of these quantities with redshift. We find that most of the total X-ray emissivity in our box originates in a relatively small number of identifiable clusters which occupy approximately 10(exp -3) of the box volume. This standard CDM model, normalized to COBE, produces approximately 5 times too much emission from clusters having L(sub x) is greater than 10(exp 43) ergs/s, a not-unexpected result. If all other parameters were unchanged, we would expect adequate agreement for sigma(sub 8) = 0.6. This provides a new and independent argument for lower small-scale power than standard CDM at the 8 h(exp -1) Mpc scale. The background radiation field at 1 keV due to clusters in this model is approximately one-third of the observed background, which, after correction for numerical effects, again indicates approximately 5 times too much emission and the appropriateness of sigma(sub 8) = 0.6. If we have used the observed ratio of gas to total mass in clusters, rather than basing the mean density on light-element nucleosynthesis, then the computed luminosity of each cluster would have increased still further, by a factor of approximately 10. The number density of clusters increases to z approximately 1, but the luminosity per typical cluster decreases, with the result that evolution in the number density of bright clusters is moderate in this redshift range, showing a broad peak near z = 0.7, and then a rapid decline above redshift z = 3. Detailed computations of the luminosity functions in the range L(sub x) = 10(exp 40) - 10(exp 44) ergs/s in various energy bands are presented for both cluster central regions and total luminosities to be used in comparison with ROSAT and other observational data sets. The quantitative results found disagree significantly with those found by other investigators using semianalytic techniques. We find little dependence of core radius on cluster luminosity and a dependence of temperature on luminosity given by log kT(sub x) = A + B log L(sub x), which is slightly steeper (B = 0.38) than is indicated by observations. Computed temperatures are somewhat higher than observed, as expected, in that COBE-normalized CDM has too much power on the relevant scales. A modest average temperature gradient is found, with temperatures dropping to 90% of central values at 0.4 h(exp -1) Mpc and 70% of central values at 0.9 h(exp -1) Mpc. Examining the ratio of gas to total mass in the clusters normalized to Omega(sub B) h(exp 2) = 0.015, and comparing with observations, we conclude, in agreement with White (1991), that the cluster observations argue for an open universe.