[Show abstract][Hide abstract] ABSTRACT: 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 90 GHz, and consider two dish diameters, 1.2 m and 2.5 m. We calculate the number density of the galaxy clusters dN/(dΩdz) at a high flux limit Svlim=100 mJy and at a relative low Svlim =10 mJy. The total numbers of SZE clusters N in two low-Ω0 models are compared. The results show that the influence of the resolved effect depends not only on D, but also on Svlim: at a given D, the effect is more significant for a high than for a low Svlim. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and Svlim =10 mJy, 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.
Preview · Article · Apr 2009 · Chinese Journal of Astronomy and Astrophysics
[Show abstract][Hide abstract] ABSTRACT: In this Letter, we study the cosmological implications of the 100 square degree Weak Lensing survey (the CFHTLS-Wide, RCS, VIRMOS-DESCART and GaBoDS surveys). We combine these weak lensing data with the cosmic microwave background (CMB) measurements from the WMAP5, BOOMERanG, CBI, VSA, ACBAR, the SDSS LRG matter power spectrum and the Type Ia Supernoave (SNIa) data with the “Union” compilation (307 sample), using the Markov Chain Monte Carlo method to determine the cosmological parameters, such as the equation-of-state (EoS) of dark energy w, the density fluctuation amplitude σ8, the total neutrino mass ∑mν and the parameters associated with the power spectrum of the primordial fluctuations. Our results show that the ΛCDM model remains a good fit to all of these data. In a flat universe, we obtain a tight limit on the constant EoS of dark energy, w=−0.97±0.041 (1σ). For the dynamical dark energy model with time evolving EoS parameterized as wde(a)=w0+wa(1−a), we find that the best-fit values are w0=−1.064 and wa=0.375, implying the mildly preference of Quintom model whose EoS gets across the cosmological constant boundary during evolution. Regarding the total neutrino mass limit, we obtain the upper limit, ∑mν<0.471 eV (95% C.L.) within the framework of the flat ΛCDM model. Due to the obvious degeneracies between the neutrino mass and the EoS of dark energy model, this upper limit will be relaxed by a factor of 2 in the framework of dynamical dark energy models. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, within the ΛCDM model, we find that the upper limit on the ratio of the tensor to scalar is r<0.35 (95% C.L.) and the inflationary models with the slope ns⩾1 are excluded at more than 2σ confidence level. In this Letter we pay particular attention to the contribution from the weak lensing data and find that the current weak lensing data do improve the constraints on matter density Ωm, σ8, ∑mν, and the EoS of dark energy.
Full-text · Article · Dec 2008 · Physics Letters B
[Show abstract][Hide abstract] ABSTRACT: Recently, the WMAP group published their 5 year data and considered the constraints on the time-evolving equation of state of dark energy for the first time from the WMAP distance information. In this Letter, we study the effectiveness of the usage of this distance information and find that the compressed CMB information can give similar constraints on dark energy parameters compared with the full CMB power spectrum if dark energy perturbations are included; however, if the dark energy perturbations are incorrectly neglected, the difference of the results is sizable.
Full-text · Article · Aug 2008 · The Astrophysical Journal
[Show abstract][Hide abstract] ABSTRACT: Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular problem has been a severe obstacle for using GRBs as cosmological candles. In this paper, we present a new method to deal with such a problem in MCMC global fitting analysis. Assuming that a certain type of correlations between different observables exists in a subsample of GRBs, for the parameters involved in the correlation relation, we treat them as free parameters and determine them simultaneously with cosmological parameters through MCMC analysis on GRB data together with other observational data. Then the circular problem is naturally eliminated in this procedure. We take the Ghirlanda relation as an example while keeping in mind the debate about its physical validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the reported Ghirlanda relation in our study, and perform MCMC global fitting. We consider the $\Lambda$CDM model and dynamical dark energy models. In each case, in addition to the constraints on the relevant cosmological parameters, we obtain the best fit values as well as the distributions of the correlation parameters $A$ and $C$. We find that the observational data sets other than GRBs can affect $A$ and $C$ considerably through their degeneracies with the cosmological parameters. The results on $A$ and $C$ for different cosmological models are in well agreement within $1\sigma$ range. The best fit value of $A$ in all models being analyzed is $A\sim 1.53$ with $\sigma \sim 0.08$. For $C$, we have the best value in the range of $0.94-0.98$ with $\sigma\sim 0.1$. It is also noted that the distributions of $A$ and $C$ are generally broader than the priors used in many studies in literature. (Abriged) Comment: 9 pages, 2 figures, 2 tables, Accepted for publication in ApJ
Preview · Article · Nov 2007 · The Astrophysical Journal
[Show abstract][Hide abstract] ABSTRACT: We consider using future redshift surveys with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to constrain the equation of state of dark energy ω. We analyze the Alcock & Paczyński (AP) effect imprinted on the two-point correlation function of galaxies in redshift space. The Fisher matrix analysis is applied to estimate the expected error bounds of ω0 and ωa from galaxy redshift surveys, ω0 and ωa being the two parameters in the equation of state parametrization ω(z) = ω0+ωaz/(1+z). Strong degeneracies between ω0 and ωa are found. The direction of the degeneracy in ω0−ωa plane, however, rotates counter-clockwise as the redshift increases. LAMOST can potentially contribute in the redshift range up to 0.5. In combination with other high redshift surveys, such as the proposed Kilo-Aperture Optical Spectrograph project (KAOS), the joint constraint derived from galaxy surveys at different redshift ranges is likely to efficiently break the degeneracy of ω0 and ωa. We do not anticipate that the nature of dark energy can be well constrained with LAMOST alone, but it may help to reduce the error bounds expected from other observations, such as the Supernova/Acceleration Probe (SNAP).
Preview · Article · Apr 2006 · Chinese Journal of Astronomy and Astrophysics
[Show abstract][Hide abstract] ABSTRACT: Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular prob- lem has been a severe obstacle for using GRBs as cosmological candles. In this paper, we present a new method to deal with such a problem in Markov Chain Monte Carlo (MCMC) global fitting analysis. Our methodology is similar t o that of self-calibrations in using clusters of galaxies as cosmological probes. Assuming that a certain type of correlations between different observables exists in a sub sample of GRBs, for the pa- rameters involved in the correlation relation, we treat the m as free parameters and de- termine them simultaneously with cosmological parameters through MCMC analysis on GRB data together with other observational data, such as SNe Ia, cosmic microwave background radiation (CMB) and large-scale structure (LSS). Then the circular prob- lem is naturally eliminated in this procedure. To demonstrate the feasibility of our method, we take the Ghirlanda relation (E ∝ CEA peak) as an example while keep- ing in mind the debate about its physical validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the reported Ghirlanda relation in our study, and perform MCMC global fitting. We consider theCDM model and dynamical dark energy models with equation of state (EoS) wDE = w0 + w1(1 − a) and the oscillating EoS wDE = w0 + w1 sin(w2 ln(a)), respectively. We also include the curvature of the universe in our analysis. In each case, in addition to the con straints on the relevant cosmological parameters, we obtain the best fit values as wel l as the distributions of the correlation parameters A and C. We find that the observational data sets other than GRBs can affect A and C considerably through their degeneracies with the cosmolog- ical parameters. With CMB+LSS+SNe+GRB data included in theanalysis, the results on A and C for different cosmological models are in well agreement within 1σ range. The best fit value of A in all models being analyzed is A ∼ 1.53 with σ ∼ 0.08. For C, we have the best value in the range of 0.94 − 0.98 with σ ∼ 0.1. It is also noted