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1.
存在于星系团电离气体中的大量高温电子会对宇宙微波背景的光子产生逆康普顿散射，引起所谓的Sunyaev-Zel‘dovich(SZ)效应，SZ效应是研究星系团的一种非常有效的手段。特别中SZ效应只与星系团的内禀性质有关，而与所处的位置无关，这有利于发现高红移的星系团，因此对星系团的演化有着极其重要的意义，正在建造中的SZ巡天望远望，将提供 条全新的确定宇宙参数的有效途径，如物质密度参量（ΩM），真空能密度参量（ΩΛ）和8h^-1Mpc尺度内的质量涨落均方差（σ8)，SZ星系团巡天确定宇宙参数，特别是定量分析利用SZ星系团巡天确定宇宙参数中可能存在的所有不确定因素，可以更好地限制宇宙学模型。在SZ星系团巡天完成之前，人们必须对这些不确定因素有清楚的了解，以便能利用未来的SZ星系团退天结果有效地测量宇宙参数。 相似文献
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在Ｘ射线观测提高了星系团质量和半径测量精度的新形势下，本文讨论了宇宙常数不等于零的平坦宇宙冷暗物质结构形成模型，利用球对称扰动区在宇宙常数不为零时的动力学方程的解，估计了星系团形成红移与宇宙常数是否为零的关系，计算了星系团质量函数随红移的演化．计算表明，红移为零时星系团的数密度基本上由谱参数Γ决定．若假定星系团质量只有２０％的不确定性，可限定Γ的适用范围约为０．１５－０．３２．高红移星系团的数密度观测不仅有可能对宇宙常数是否为零作出鉴别，而且当精度够高时还能对宇宙物质密度的大小作出限制 相似文献
3.
该文研究了以星系作为透镜体产生的切向弧(即"爱因斯坦环")的强引力透镜现象,并对该领域近年来的观测和研究作了总结.对形成这些强引力透镜"环"的星系所进行的研究表明,其附近存在的质量所产生的会聚和剪切对透镜的质量分布模型非常敏感.在大视场巡天中找到的这种爱因斯坦环的数目相当多,大约是每平方度10个,其中"强引力透镜巡天"(Strong LensingLegacy Survey,SL2S)提供了大量处于星系团视场中的由椭圆星系产生的爱因斯坦环样本.系统地研究星系团外围存在的爱因斯坦环,一方面可以理解星系团环境对爱因斯坦环的影响,另一方面可以利用它们来探测星系团的物质分布,并进而对冷暗物质宇宙学提供新的探测方法. 相似文献
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二维与三维星系巡天观测表明,存在着长纤维状超星系团和巨大的空洞。邻近超星系团的详细研究表明它们互相连通而形成巨大的网络。有效的定量识别图案的集团分析方法用于大天区三维巡天资料,使上述直观印象进一步得到了证实。星系分布的这些特征和它们的拓补结构,可以用绝热模型解释。更深度的巡天观测,多粒子数值模拟和进一步的理论研究正在进行中,会在不久的将来进一步揭示星系在大尺度上的分布特征。 相似文献
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该文利用高精度的大尺度N体数值模拟,研究了WMAP(Wilkinson Microwave Anisotropy Probe)第3年的观测结果对星系团中的巨弧数目的影响,发现预言的巨弧数目比主流的ACDM模型预言的要低80%多。加入绝热气体几乎不会改变巨弧的发生概率,而引入恒星形成和超新星反馈后得到的概率不会大于原来的1.3倍。如此小的贡献是因为虽然有恒星的数值模拟得到的星系团具有更高的中心密度,但同时星系团的形状更趋球对称,这是影响巨弧概率的2个相反的因素。以前基于ACDM模型预言的巨弧概率还不能很好地与观测相符,WMAP第3年的观测结果将更难以解释。 相似文献
8.
基于目前流行的冷暗物质等级成团理论的星系形成的半解析模型取得了很大进展．在引入一系列合理的关于重子物质物理过程的假设，如气体冷却、恒星形成率、超新星能量反馈以后，结合N体数值模拟，星系形成的半解析模型一方面能较成功地预言许多与观测符合的近邻星系的性质，如光度函数、星系的两点相关函数、Thlly-Fisher关系、星系团中椭圆星系的颜色一星等关系等；另一方面还能较成功地预言宇宙的恒星形成历史，以及一部分高红移星系的性质，如Lyman-Break星系的数目随红移的分布．但是最近一些观测表明，半解析模型在高红移预言的大质量星系较少，且红星系数目也较观测少．重点讨论半解析模型成功与不足之处，并指出解决这些问题可能的途径。 相似文献
9.
倾斜冷暗物质谱与宇宙中可观测结构 总被引：1，自引：1，他引：0
为了缓解标准冷暗物质模型在解释一些观测现象时所遇到的困难，本考察了倾斜冷暗物质谱模型。在ＢＢＫＳ原初扰动场统计理论的基础上，本根据天体质量函数的计算公式和背景－天体相互作用的估计方法，计算了星系群和星系团的质量函数，并与最新观测质量函数作了对比，又分析和计算了在各种空洞尺度上天体密度的变化。计算结果表明，倾斜冷暗物质谱模型在与ＣＯＢＥ卫星观测结果相容的前提下，能在上述两个方面缓解标准冷暗物质模 相似文献
10.
马駬 《中国天文和天体物理学报》1995,(1)
为了缓解标准冷暗物质模型在解释一些观测现象时所遇到的困难，本文考察了倾斜冷暗物质谱模型。在ＢＢＫＳ原初扰动场统计理论的基础上，本文根据天体质量函数的计算公式和背景－天体相互作用的估计方法，计算了星系群和星系团的质量函数，并与最新观测质量函数作了对比，又分析和计算了在各种空洞尺度上天体密度的变化。计算结果表明，倾斜冷暗物质谱模型在与ＣＯＢＥ卫星观测结果相容的前提下，能在上述两个方面缓解标准冷暗物质模型所遇到的困难。 相似文献
11.
Jia-Yu Tang Zu-Hui FanDepartment of Astronomy Peking University Beijing tangjy@vega.bac.pku.edu.cnChinese Academy of Sciences-Peking University Joint Beijing Astrophysics Center Beijing 《中国天文和天体物理学报》2003,3(3):191-202
We study the counts of resolved SZE(Sunyaev-Zel‘dovich effect)clusters expected from an interferometric survey in different cosmological models under different conditions.The self-similar universal gas model and Press-Schechter mass function are used.We take the observing frequency to be 90GHz,and consider two dish diameters,1.2m and 2.5m.We calculate the number density of the galaxy clusters dN/(dΩdz)at a high flux limit Sv^lim=100mJy and at a relative low Sv^lim=10mJy.The total numbers of SZE clusters N in two low-Ω0 models are compared.The results show that the inθuence of the resolved effect depends not only on D,but also on Sv^lim;at a given D,the effect is more significant for a high than for a low Sv^lim.Also,the resolved effect for a flat universe is more impressive than tnat for an open universe.ForD=1.2m and Sv^lim=10mJy,the resolved effect is very weak.Considering the designed interferometers which will be used to survey SZE clusters,we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys. 相似文献
12.
《Chinese Astronomy and Astrophysics》2006,30(2):121-132
In the near future a large number of galaxy clusters will be observed in surveys based on the Sunyaev-Zel'dovich effect (SZE) . Both the spherical and ellipsoidal models of the dark matter of galaxy clusters are adopted to make theoretical predictions of the number of observable S-Z galaxy clusters, and to asses the effect of the cluster shape on the calculation. By means of the virial equilibrium condition the mass lower limit of the observable galaxy clusters is determined from given survey flux lower limit and the prediction of the number count of galaxy clusters is carried out by the mass function. The calculated results show that if the cosmological parameters are to be constrained by the S-Z surveys, then the uncertainty in the shape of the clusters should be taken into account. 相似文献
13.
J. M. Diego J. Mohr J. Silk G. Bryan 《Monthly notices of the Royal Astronomical Society》2003,341(2):599-608
We develop a new method to estimate the redshift of galaxy clusters through resolved images of the Sunyaev–Zel'dovich effect (SZE). Our method is based on morphological observables which can be measured by actual and future SZE experiments. We test the method with a set of high-resolution hydrodynamical simulations of galaxy clusters at different redshifts. Our method combines the observables in a principal component analysis. After calibrating the method with an independent redshift estimation for some of the clusters, we show – using a Bayesian approach – how the method can give an estimate of the redshift of the galaxy clusters. Although the error bars given by the morphological redshift estimation are large, it should be useful for future SZE surveys where thousands of clusters are expected to be detected; a first preselection of the high-redshift candidates could be done using our proposed morphological redshift estimator. Although not considered in this work, our method should also be useful to give an estimate of the redshift of clusters in X-ray and optical surveys. 相似文献
14.
L. Moscardini S. Matarrese F. Lucchin P. Rosati 《Monthly notices of the Royal Astronomical Society》2000,316(2):283-298
We present a model to predict the clustering properties of X-ray selected clusters in flux-limited surveys. Our technique correctly accounts for past light-cone effects on the observed clustering and follows the non-linear evolution in redshift of the underlying dark matter correlation function and cluster bias factor. The conversion of the limiting flux of a survey into the corresponding minimum mass of the hosting dark matter haloes is obtained by using theoretical and empirical relations between mass, temperature and X-ray luminosity of galaxy clusters. Finally, our model is calibrated to reproduce the observed cluster counts adopting a temperature–luminosity relation moderately evolving with redshift. We apply our technique to three existing catalogues: the ROSAT Brightest Cluster Sample (BCS); the X-ray Brightest Abell-type Cluster sample (XBACs); and the ROSAT –ESO Flux-Limited X-ray sample (REFLEX). Moreover, we consider an example of possible future space missions with fainter limiting flux. In general, we find that the amplitude of the spatial correlation function is a decreasing function of the limiting flux and that the Einstein–de Sitter models always give smaller correlation amplitudes than open or flat models with low matter density parameter Ω0m . In the case of the XBACs catalogue, the comparison with previous estimates of the observational spatial correlation shows that only the predictions of models with Ω0m =0.3 are in good agreement with the data, while the Einstein–de Sitter models have too low a correlation strength. Finally, we use our technique to discuss the best strategy for future surveys. Our results show that, to study the clustering properties of X-ray selected clusters, the choice of a wide area catalogue, even with a brighter limiting flux, is preferable to a deeper, but smaller area, survey. 相似文献
15.
J. M.Diego E.Martínez-González J. L.Sanz N.Benitez J.Silk 《Monthly notices of the Royal Astronomical Society》2002,331(3):556-568
We show how future measurements of the Sunyaev–Zel'dovich effect (SZE) can be used to constrain the cosmological parameters. We combine the SZ information expected from the Planck full-sky survey, N ( S ), where no redshift information is included, with the N ( z ) obtained from an optically identified SZ-selected survey covering less than 1 per cent of the sky. We demonstrate how with a small subsample (≈300 clusters) of the whole SZ catalogue observed optically it is possible to reduce the degeneracy among the cosmological parameters drastically. We have studied the requirements for performing the optical follow-up and we show the feasibility of such a project. Finally, we have compared the cluster expectations for Planck with those expected for Newton–XMM during their lifetimes. It is shown that, owing to its larger sky coverage, Planck will detect a factor of ∼5 times more clusters than Newton–XMM and also provide a larger redshift coverage. 相似文献
16.
J. M. Ferreira 《Monthly notices of the Royal Astronomical Society》2000,316(3):647-656
We analyse the spatial clustering properties of the ROSAT All-Sky Survey (RASS) 1 Bright Sample, an X-ray flux-limited catalogue of galaxy clusters selected from the southern part of the survey. The two-point correlation function ( r ) of the whole sample is well fitted (in an Einsteinde Sitter model) by the power law =( r r 0 ) , with and (95.4 per cent confidence level with one fitting parameter). We use the RASS 1 Bright Sample as a first application of a theoretical model that aims to predict the clustering properties of X-ray clusters in flux-limited surveys for different cosmological scenarios. The model uses the theoretical and empirical relations between mass, temperature and X-ray cluster luminosity, and fully accounts for the redshift evolution of the underlying dark matter clustering and cluster bias factor. The comparison between observational results and theoretical predictions shows that the Einsteinde Sitter models display too low a correlation length, while models with a matter density parameter 0m =0.3 (with or without a cosmological constant) are successful in reproducing the observed clustering. The dependence of the correlation length r 0 on the X-ray limiting flux and luminosity of the sample is generally consistent with the predictions of all our models. Quantitative agreement is however only reached for 0m =0.3 models. The model presented here can be reliably applied to future deeper X-ray cluster surveys: the study of the clustering properties will provide a useful complementary tool to the traditional cluster abundance analyses used to constrain the cosmological parameters. 相似文献
17.
H. Bhringer 《Astronomische Nachrichten》2008,329(2):135-138
18.
Rados&#;aw Wojtak Ewa L. &#;okas 《Monthly notices of the Royal Astronomical Society》2007,377(2):843-854
We study the effect of contamination by interlopers in kinematic samples of galaxy clusters. We demonstrate that without the proper removal of interlopers the inferred parameters of the mass distribution in the cluster are strongly biased towards higher mass and lower concentration. The interlopers are removed using two procedures previously shown to work most efficiently on simulated data. One is based on using the virial mass estimator and calculating the maximum velocity available to cluster members and the other relies on the ratio of the virial and projected mass estimators. We illustrate the performance of the methods in detail using the example of A576, a cluster with a strong uniform background contamination, and compare the case of A576 to 15 other clusters with different degree of contamination. We model the velocity dispersion and kurtosis profiles obtained for the cleaned data samples of these clusters solving the Jeans equations to estimate the mass, concentration and anisotropy parameter. We present the mass–concentration relation for the total sample of 22 clusters. 相似文献
19.
J.-J. Fleck C. M. Boily A. Lançon S. Deiters 《Monthly notices of the Royal Astronomical Society》2006,369(3):1392-1406
The mass of unresolved young star clusters derived from spectrophotometric data may well be off by a factor of 2 or more once the migration of massive stars driven by mass segregation is accounted for. We quantify this effect for a large set of cluster parameters, including variations in the stellar initial mass function (IMF), the intrinsic cluster mass, and mean mass density. Gas-dynamical models coupled with the Cambridge stellar evolution tracks allow us to derive a scheme to recover the real cluster mass given measured half-light radius, one-dimensional velocity dispersion and age. We monitor the evolution with time of the ratio of real to apparent mass through the parameter η. When we compute η for rich star clusters, we find non-monotonic evolution in time when the IMF stretches beyond a critical cut-off mass of 25.5 M⊙ . We also monitor the rise of colour gradients between the inner and outer volume of clusters: we find trends in time of the stellar IMF power indices overlapping well with those derived for the Large Magellanic Cloud cluster NGC 1818 at an age of 30 Myr. We argue that the core region of massive Antennae clusters should have suffered from much segregation despite their low ages. We apply these results to a cluster mass function, and find that the peak of the mass distribution would appear to observers shifted to lower masses by as much as 0.2 dex. The star formation rate derived for the cluster population is then underestimated by from 20 to 50 per cent. 相似文献
20.
Rados&#;aw Wojtak Ewa L. &#;okas Gary A. Mamon Stefan Gottlöber 《Monthly notices of the Royal Astronomical Society》2009,399(2):812-821
We present a new method of constraining the mass and velocity anisotropy profiles of galaxy clusters from kinematic data. The method is based on a model of the phase-space density, which allows the anisotropy to vary with radius between two asymptotic values. The characteristic scale of transition between these asymptotes is fixed and tuned to a typical anisotropy profile resulting from cosmological simulations. The model is parametrized by two values of anisotropy, at the centre of the cluster and at infinity, and two parameters of the NFW density profile, the scale radius and the scale mass. In order to test the performance of the method in reconstructing the true cluster parameters, we analyse mock kinematic data for 20 relaxed galaxy clusters generated from a cosmological simulation of the standard Λ cold dark matter model. We use Bayesian methods of inference and the analysis is carried out following the Markov Chain Monte Carlo approach. The parameters of the mass profile are reproduced quite well, but we note that the mass is typically underestimated by 15 per cent, probably due to the presence of small velocity substructures. The constraints on the anisotropy profile for a single cluster are in general barely conclusive. Although the central asymptotic value is determined accurately, the outer one is subject to significant systematic errors caused by substructures at large clustercentric distance. The anisotropy profile is much better constrained if one performs joint analysis of at least a few clusters. In this case, it is possible to reproduce the radial variation of the anisotropy over two decades in radius inside the virial sphere. 相似文献