共查询到20条相似文献，搜索用时 15 毫秒
1.
Pia Mukherjee Andrew R. Liddle 《Monthly notices of the Royal Astronomical Society》2008,389(1):231-236
We use Bayesian model selection tools to forecast the Planck satellite's ability to distinguish between different models for the re-ionization history of the Universe, using the large angular scale signal in the cosmic microwave background polarization spectrum. We find that Planck is not expected to be able to distinguish between an instantaneous re-ionization model and a two-parameter smooth re-ionization model, except for extreme values of the additional re-ionization parameter. If it cannot, then it will be unable to distinguish between different two-parameter models either. However, Bayesian model averaging will be needed to obtain unbiased estimates of the optical depth to re-ionization. We also generalize our results to a hypothetical future cosmic variance limited microwave anisotropy survey, where the outlook is more optimistic. 相似文献
2.
Luigi Ferraioli Edward K. Porter Michele Armano Heather Audley Giuseppe Congedo Ingo Diepholz Ferran Gibert Martin Hewitson Mauro Hueller Nikolaos Karnesis Natalia Korsakova Miquel Nofrarias Eric Plagnol Stefano Vitale 《Experimental Astronomy》2014,37(1):109-125
We present a parameter estimation procedure based on a Bayesian framework by applying a Markov Chain Monte Carlo algorithm to the calibration of the dynamical parameters of the LISA Pathfinder satellite. The method is based on the Metropolis-Hastings algorithm and a two-stage annealing treatment in order to ensure an effective exploration of the parameter space at the beginning of the chain. We compare two versions of the algorithm with an application to a LISA Pathfinder data analysis problem. The two algorithms share the same heating strategy but with one moving in coordinate directions using proposals from a multivariate Gaussian distribution, while the other uses the natural logarithm of some parameters and proposes jumps in the eigen-space of the Fisher Information matrix. The algorithm proposing jumps in the eigen-space of the Fisher Information matrix demonstrates a higher acceptance rate and a slightly better convergence towards the equilibrium parameter distributions in the application to LISA Pathfinder data. For this experiment, we return parameter values that are all within ～1σ of the injected values. When we analyse the accuracy of our parameter estimation in terms of the effect they have on the force-per-unit of mass noise, we find that the induced errors are three orders of magnitude less than the expected experimental uncertainty in the power spectral density. 相似文献
3.
Martin White Yong-Seon Song Will J. Percival 《Monthly notices of the Royal Astronomical Society》2009,397(3):1348-1354
Observations of redshift-space distortions in spectroscopic galaxy surveys offer an attractive method for observing the build-up of cosmological structure, which depends both on the expansion rate of the Universe and our theory of gravity. In this paper, we present a formalism for forecasting the constraints on the growth of structure which would arise in an idealized survey. This Fisher matrix based formalism can be used to study the power and aid in the design of future surveys. 相似文献
4.
We develop a general formalism for analysing parameter information from non-Gaussian cosmic fields. The method can be adapted to include the non-linear effects in galaxy redshift surveys, weak lensing surveys and cosmic velocity field surveys as part of parameter estimation. It can also be used as a test of non-Gaussianity of the cosmic microwave background. Generalizing maximum-likelihood analysis to second order, we calculate the non-linear Fisher information matrix and likelihood surfaces in parameter space. To this order we find that the information content is always increased by including non-linearity. Our methods are applied to a realistic model of a galaxy redshift survey, including non-linear evolution, galaxy bias, shot-noise and redshift-space distortions to second order. We find that including non-linearities allows all of the degeneracies between parameters to be lifted. Marginalized parameter uncertainties of a few per cent will then be obtainable using forthcoming galaxy redshift surveys. 相似文献
5.
P. J. Marshall M. P. Hobson A. Slosar 《Monthly notices of the Royal Astronomical Society》2003,346(2):489-500
As the quality of the available galaxy cluster data improves, the models fitted to these data might be expected to become increasingly complex. Here we present the Bayesian approach to the problem of cluster data modelling: starting from simple, physically motivated parametrized functions to describe the cluster's gas density, gravitational potential and temperature, we explore the high-dimensional parameter spaces with a Markov-Chain Monte Carlo sampler, and compute the Bayesian evidence in order to make probabilistic statements about the models tested. In this way sufficiently good data will enable the models to be distinguished, enhancing our astrophysical understanding; in any case the models may be marginalized over in the correct way when estimating global, perhaps cosmological, parameters. In this work we apply this methodology to two sets of simulated interferometric Sunyaev–Zel'dovich effect and gravitational weak lensing data, corresponding to current and next-generation telescopes. We calculate the expected precision on the measurement of the cluster gas fraction from such experiments, and investigate the effect of the primordial cosmic microwave background (CMB) fluctuations on their accuracy. We find that data from instruments such as the Arcminute Microkelvin Imager (AMI), when combined with wide-field ground-based weak lensing data, should allow both cluster model selection and estimation of gas fractions to a precision of better than 30 per cent for a given cluster. 相似文献
6.
主要研究了修改引力论在非线性尺度上的表现。现在已经存在很多修改引力论的模型,如f（R）,DGP,Mond等,但是在工作中并没有使用别人已经提出的修改引力论方法,因为首先不可能去对所有的修改引力论模型都进行研究;其次重点研究的是修改引力对于宇宙中的物质分布在非线性尺度上的影响,而各种修改引力论对于物质聚集的影响是相似的,都可以通过一个参数表达出来。因此笔者提出一种修改引力论的方法,引进了一个简单参数ζ。这个参数ζ定义为Geff/G/-φ/Ψ,这里Geff是有效牛顿常数,G是牛顿常数,φ和Ψ则是时空度规的标量扰动方程中的两个势。这个ζ参数在广义相对论的基础上修改了物质粒子受到的加速度,加大或者减小这个参数会相应地改变物质粒子的加速度,进而会加快或者减慢大尺度结构的形成。这种对大尺度结构在线性尺度上的影响可以通过理论计算得到,但是大尺度结构的非线性增长无法通过理论计算得出,现在只有借助已经发展得比较成熟的数值模拟方法来研究这个问题。该文修改了现在已经比较成熟的数值模拟程序GADGET-2,加入了ζ参数。在进行数值模拟之前,首先检验了数值模拟的质量分辨率、模拟尺度,以及初始红移对最终物质功率谱的影响,并且证实修改后的GADGET-2程序是正确的。设定不同ζ参数的值,ζ=0.8,0.9,1.0,1.1,1.2,1.5,这里ζ=1.0对应标准宇宙学,然后对每个ζ值运行了一组数值模拟。为了减少数值效应对最终结果的影响,并且突出显示修改引力论在非线性尺度上的表现,没有简单直接地使用不同ζ值物质功率谱来做比较,而是精巧地设置不同ζ值的输出红移,使不同ζ值在其对应的输出红移处有相同的线性功率谱,并且最终使用了ξ=ζ≠1.0/ζ=1.0这个比值参数来研究修改引力论在非线性尺度上的表现。通过宇宙学尺度上的数值模拟和高精度的小波物质功率谱方法,我们研究了ζ参数对物质在非线性尺度上增长的影响。通过ξ这个参数,在线性功率谱相同的时候,比较了不同ζ参数的功率谱在非线性尺度上相对于标准宇宙学模型的偏离。得到重大的发现:大尺度结构在非线性上的增长并不是想象的那样,较大的ζ参数加大了物质粒子的加速度,进而在线性和非线性尺度上都加快了结构形成,反而是在线性功率谱相同的时候,较大值的ζ给出了较小的非线性功率谱。这个发现也证明HKLM假定的不正确,从而证明基于这个假定的功率谱拟合公式（PD96,Smith2003）不适用于修改引力论,直接将这些功率谱拟合公式推广到修改引力论是不正确的。基于这个ζ参数的修改引力论模型,利用一系列的数值模拟的结果,为修改引力论提出了一个新的拟合公式。这个新的拟合公式不是对现有的这些拟合公式做推广,而是借助于标准宇宙学下的非线性功率谱,通过几个简单的参数就可以得到对应不同ζ值的非线性功率谱,而且其精度保证在5%以内。利用这套数值模拟的结果,我们进而研究ζ修改引力论下的本动速度场的功率谱、暗晕的质量方程,以及暗晕的性质。这些工作为我们从观测上区分修改引力论和广义相对论提供了理论指导。 相似文献
7.
Although it is well known that any consideration of the variations of fundamental constants should be restricted to their dimensionless combinations, the literature on variations of the gravitational constant G is entirely dimensionfull. To illustrate applications of this to cosmology, we explicitly give a dimensionless version of the parameters of the standard cosmological model, and describe the physics of both Big Bang Nucleosynthesis and recombination in a dimensionless manner. Rigorously determining how to talk about the model in a way which avoids physical dimensions is a requirement for proceeding with a calculation to constrain time-varying fundamental constants. The issue that appears to have been missed in many studies is that in cosmology the strength of gravity is bound up in the cosmological equations, and the epoch at which we live is a crucial part of the model. We argue that it is useful to consider the hypothetical situation of communicating with another civilization (with entirely different units), comparing only dimensionless constants, in order to decide if we live in a Universe governed by precisely the same physical laws. In this thought experiment, we would also have to compare epochs, which can be defined by giving the value of any one of the evolving cosmological parameters. By setting things up carefully in this way one can avoid inconsistent results when considering variable constants, caused by effectively fixing more than one parameter today. We show examples of this effect by considering microwave background anisotropies, being careful to maintain dimensionlessness throughout. We present Fisher matrix calculations to estimate how well the fine structure constants for electromagnetism and gravity can be determined with future microwave background experiments. We highlight how one can be misled by simply adding G to the usual cosmological parameter set. 相似文献
8.
Farhan Feroz Michael P. Hobson Jonathan T. L. Zwart Richard D. E. Saunders Keith J. B. Grainge 《Monthly notices of the Royal Astronomical Society》2009,398(4):2049-2060
We present a Bayesian approach to modelling galaxy clusters using multi-frequency pointed observations from telescopes that exploit the Sunyaev–Zel'dovich effect. We use the recently developed multinest technique to explore the high-dimensional parameter spaces and also to calculate the Bayesian evidence. This permits robust parameter estimation as well as model comparison. Tests on simulated Arcminute Microkelvin Imager observations of a cluster, in the presence of primary CMB signal, radio point sources (detected as well as an unresolved background) and receiver noise, show that our algorithm is able to analyse jointly the data from six frequency channels, sample the posterior space of the model and calculate the Bayesian evidence very efficiently on a single processor. We also illustrate the robustness of our detection process by applying it to a field with radio sources and primordial CMB but no cluster, and show that indeed no cluster is identified. The extension of our methodology to the detection and modelling of multiple clusters in multi-frequency SZ survey data will be described in a future work. 相似文献
9.
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
10.
Pedro Carvalho Graça Rocha M. P. Hobson 《Monthly notices of the Royal Astronomical Society》2009,393(3):681-702
A new fast Bayesian approach is introduced for the detection of discrete objects immersed in a diffuse background. This new method, called PowellSnakes, speeds up traditional Bayesian techniques by (i) replacing the standard form of the likelihood for the parameters characterizing the discrete objects by an alternative exact form that is much quicker to evaluate; (ii) using a simultaneous multiple minimization code based on Powell's direction set algorithm to locate rapidly the local maxima in the posterior and (iii) deciding whether each located posterior peak corresponds to a real object by performing a Bayesian model selection using an approximate evidence value based on a local Gaussian approximation to the peak. The construction of this Gaussian approximation also provides the covariance matrix of the uncertainties in the derived parameter values for the object in question. This new approach provides a speed up in performance by a factor of '100' as compared to existing Bayesian source extraction methods that use Monte Carlo Markov chain to explore the parameter space, such as that presented by Hobson & McLachlan. The method can be implemented in either real or Fourier space. In the case of objects embedded in a homogeneous random field, working in Fourier space provides a further speed up that takes advantage of the fact that the correlation matrix of the background is circulant. We illustrate the capabilities of the method by applying to some simplified toy models. Furthermore, PowellSnakes has the advantage of consistently defining the threshold for acceptance/rejection based on priors which cannot be said of the frequentist methods. We present here the first implementation of this technique (version I). Further improvements to this implementation are currently under investigation and will be published shortly. The application of the method to realistic simulated Planck observations will be presented in a forthcoming publication. 相似文献
11.
T. Appourchaux 《Astronomische Nachrichten》2008,329(5):485-489
Nowadays, g‐mode detection is based upon a priori theoretical knowledge. By doing so, detection becomes more restricted to what we can imagine. De facto, the universe of possibilities ismade narrower. Such an approach is pertinent for Bayesian statisticians. Examples of how Bayesian inferences can be applied to spectral analysis and helioseismic power spectra are given. Our intention is not to give the full statistical framework (much too ambitious) but to provide an appetizer for going further in the direction of a proper Bayesian inference, especially for detecting gravity modes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
Steve Hatton † 《Monthly notices of the Royal Astronomical Society》1999,310(4):1128-1136
Recent results from a number of redshift surveys suggest that the Universe is well described by an inhomogeneous, fractal distribution on the largest scales probed. This distribution has been found to have fractal dimension, D , approximately equal to 2.1, in contrast to a homogeneous distribution in which the dimension should approach the value 3 as the scale is increased. In this paper we demonstrate that estimates of D , based on the conditional density of galaxies, are prone to bias from several sources. These biases generally result in a smaller measured fractal dimension than the true dimension of the sample. We illustrate this behaviour in application to the Stromlo–APM redshift survey, showing that this data set in fact provides evidence for fractal dimension increasing with survey depth. On the largest scale probed, r ≈60 h −1 Mpc, we find evidence for a distribution with dimension D =2.76±0.10. A comparison between this sample and mock Stromlo–APM catalogues taken from N -body simulations (which assume a CDM cosmology) reveals a striking similarity in the behaviour of the fractal dimension. Thus we find no evidence for inhomogeneity in excess of that expected from conventional cosmological theory. We consider biases affecting future large surveys and demonstrate, using mock SDSS catalogues, that this survey will be able to measure the fractal dimension on scales at which we expect to see full turn-over to homogeneity, in an accurate and unbiased way. 相似文献
13.
We explore the prospects for using future supernova observations to probe the dark energy. We focus on quintessence, an evolving scalar field that has been suggested as a candidate for the dark energy. After simulating the observations that would be expected from the proposed SuperNova / Acceleration Probe satellite ( SNAP ), we investigate two methods for extracting information concerning quintessence from such data. First, by expanding the quintessence equation of state as w Q ( z ) = w Q (0) −α ln(1 + z ) , to fit the data, it is possible to reconstruct the quintessence potential for a wide range of smoothly varying potentials. Secondly, it will be possible to test the basic properties of the dark energy by constraining the parameters Ω Q , w Q and α. We show that it may be possible, for example, to distinguish between quintessence and the cosmological constant in this way. Furthermore, when supernova data are combined with other planned cosmological observations, the precision of reconstructions and parameter constraints is significantly improved, allowing a wider range of dark energy models to be distinguished. 相似文献
14.
The relation between gravity anomalies, topography and volcanism can yield important insights about the internal dynamics of planets. From the power spectra of gravity and topography on Earth, Venus and Mars we infer that gravity anomalies have likely predominantly sources below the lithosphere up to about spherical harmonic degree l=30 for Earth, 40 for Venus and 5 for Mars. To interpret the low-degree part of the gravity spectrum in terms of possible sublithospheric density anomalies we derive radial mantle viscosity profiles consistent with mineral physics. For these viscosity profiles we then compute gravity and topography kernels, which indicate how much gravity anomaly and how much topography is caused by a density anomaly at a given depth. With these kernels, we firstly compute an expected gravity-topography ratio. Good agreement with the observed ratio indicates that for Venus, in contrast to Earth and Mars, long-wavelength topography is largely dynamically supported from the sublithospheric mantle. Secondly, we combine an empirical power spectrum of density anomalies inferred from seismic tomography in Earth’s mantle with gravity kernels to model the gravity power spectrum. We find a good match between modeled and observed gravity power spectrum for all three planets, except for 2?l?4 on Venus. Density anomalies in the Venusian mantle for these low degrees thus appear to be very small. We combine gravity kernels and the gravity field to derive radially averaged density anomaly models for the Martian and Venusian mantles. Gravity kernels for l?5 are very small on Venus below ≈800 km depth. Thus our inferences on Venusian mantle density are basically restricted to the upper 800 km. On Mars, gravity anomalies for 2?l?5 may originate from density anomalies anywhere within its mantle. For Mars as for Earth, inferred density anomalies are dominated by l=2 structure, but we cannot infer whether there are features in the lowermost mantle of Mars that correspond to Earth’s Large Low Shear Velocity Provinces (LLSVPs). We find that volcanism on Mars tends to occur primarily in regions above inferred low mantle density, but our model cannot distinguish whether or not there is a Martian analog for the finding that Earth’s Large Igneous Provinces mainly originate above the margins of LLSVPs. 相似文献
15.
Timothy G. Clemson Andrew R. Liddle 《Monthly notices of the Royal Astronomical Society》2009,395(3):1585-1590
We use a dynamical systems approach to study thawing quintessence models, using a multiparameter extension of the exponential potential which can approximate the form of typical thawing potentials. We impose observational constraints using a compilation of current data, and forecast the tightening of constraints expected from future dark energy surveys, as well as discussing the relation of our results to analytical constraints already in the literature. 相似文献
16.
17.
We study some holographic dark energy models in chameleonic Brans-Dicke field gravity by taking interaction between the dark energy components in FRW universe. Firstly, we take the holographic dark energy model with Granda-Oliveros cut-off and discuss interacting as well as non-interacting cases. Secondly, we consider the holographic dark energy with both power-law as well as logarithmic corrections using Hubble scale as infrared cut-off in interacting case only. We describe the evolution of some cosmological parameters for these holographic dark energy models. It is concluded that the phantom crossing can be achieved more easily in the presence of chameleonic Brans-Dicke field as compared to simple Brans-Dicke as well as Einstein’s gravity. Also, the deceleration parameter strongly confirms the accelerated expanding behavior of the universe. 相似文献
18.
Philippe Prugniel 《中国天文和天体物理学报》2011,(8)
A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package,we have tested the effect of different resolutions and signal-tonoise ratios(SNR) on the measurement of the stellar atmospheric parameters(effective temperature Teff,surface gravity log g,and metallicity [Fe/H]) . We show that ULySS is reliable for determ... 相似文献
19.
Andrew A. de Lai & Glenn D. Starkman 《Monthly notices of the Royal Astronomical Society》1998,299(4):977-984
We analyse the window functions for the spherical harmonic mode estimators of all-sky, volume-limited surveys, considering evolutionary effects along the past light-cone which include the deviation of the distance scale from a linear relationship with redshift, linear peculiar velocity corrections, and linear evolution of the density perturbations. The spherical harmonic basis functions are considered, because they correspond most closely to the symmetries of typical survey geometries and of the light-cone effects we consider. Our results show substantial broadening of the windows over that expected by ignoring light-cone effects, indicating the difficulty of measuring the power spectrum independently from cosmology. We suggest that because of light-cone effects, deep redshift surveys should be analysed either in conjunction with CMBR data which determines the cosmological parameters, or by using a Bayesian likelihood scheme in which varying cosmological parameters and a simple parametrization of the primordial power spectrum are assumed as the priors, so that observed data can be mapped from redshift to real space. The derived power spectrum can then be compared with underlying models of fluctuation generation and growth in structure formation to evaluate both these models and the cosmological priors. 相似文献