张同杰，学者全讯担保网主页-全讯担保网

we employ an analytical approach to investigate the signatures of baryon acoustic oscillations(baos) on the convergence power spectrum of weak lensing by large scale structure. it is shown that the baos wiggles can be found in both of the linear and nonlinear convergence power spectra of weak lensing at about 40≤1≤600, but they are weaker than that of matter power spectrum. although the statistical error for lsst are greatly smaller than that of cfht and snap survey especially at about 30<1<300, they are still larger than their maximum variations of baos wiggles. thus, the detection of baos with the ongoing and upcoming surveys such as lsst, cfht and snap survey confront a technical challenge.

it has been revealed recently that, in the scale free range, i.e. from the scale of the onset of nonlinear evolution to the scale of dissipation, the velocity and mass density fields of cosmic baryon fluid are extremely well described by the self-similar log-poisson hierarchy. as a consequence of this evolution, the relations among various physical quantities of cosmic baryon fluid should be scale invariant, if the physical quantities are measured in cells on scales larger than the dissipation scale, regardless the baryon fluid is in virialized dark halo, or in pre-virialized state. we examine this property with the relation between the compton parameter of the thermal sunyaev-zel'dovich effect, y(r), and x-ray luminosity, lx(r), where r being the scale of regions in which y and lx are measured. according to the self-similar hierarchical scenario of nonlinear evolution, one should expect that 1.) in the y(r)-lx(r) relation, y(r)=10a(r)[lx(r)](r), the coefficients a(r) and (r) are scale-invariant; 2.) the relation y(r)=10a(r)[lx(r)] (r) given by cells containing collapsed objects is also available for cells without collapsed objects, only if r is larger than the dissipation scale. these two predictions are well established with a scale decomposition analysis of observed data, and a comparison of observed y(r)-lx(r) relation with hydrodynamic simulation samples. the implication of this result on the characteristic scales of non-gravitational heating is also addressed.

we apply the statefinder diagnostic to the modified polytropic cardassian universe in this work. we find that the statefinder diagnostic is quite effective to distinguish cardassian models from a series of other cosmological models. the s-r plane is used to classify the modified polytropic cardassian models into six cases. the evolutionary trajectories in the s-r plane for the cases with different and reveal different evolutionary properties of the universe. in addition, we combine the observational h(z) data, the cosmic microwave background data and the baryonic acoustic oscillation data to make a joint analysis. we find that case 2 can be excluded at the 68.3% confidence level and any case is consistent with the observations at the 95.4% confidence level.

in this work, we use observations of the hubble parameter from the differential ages of passively evolving galaxies and the recent detection of the baryon acoustic oscillations (bao) at z1=0.35 to constrain the dvali-gabadadze-porrati (dgp) universe. for the case with a curvature term, we set a prior h=0.73±0.03 and the best-fit values suggest a spatially closed universe. for a flat universe, we set h free and we get consistent results with other recent analyses.

using the absolute ages of passively evolving galaxies observed at different redshifts, one can obtain the differential ages, the derivative of redshift z with respect to the cosmic time t (i.e. dz/dt). thus, the hubble parameter h(z) can be measured through the relation h(z)=−(dz/dt)/(1 z). by comparing the measured hubble parameter at different redshifts with the theoretical one containing free cosmological parameters, one can constrain current cosmological models. in this paper, we use this method to present the constraint on a spatially flat friedmann-robert-walker universe with a matter component and a holographic dark energy component, in which the parameter c plays a significant role in this dark energy model. firstly we consider three fixed values of c=0.6, 1.0 and 1.4 in the fitting of data. if we set c free, the best fitting values are c=0.26, m0=0.16, h=0.9998. it is shown that the holographic dark energy behaves like a quintom-type at the 1 level. this result is consistent with some other independent cosmological constrains, which imply that c<1.0 is favored. we also test the results derived from the differential ages using another independent method based on the lookback time to galaxy clusters and the age of the universe. it shows that our results are reliable.

we study the x-ray emission of baryon fluid in the universe using the wigeon cosmological hydrodynamic simulations. it has been revealed that cosmic baryon fluid in the nonlinear regime behaves like burgers turbulence, i.e. the fluid field consists of shocks. like turbulence in incompressible fluid, the burgers turbulence plays an important role in converting the kinetic energy of the fluid to thermal energy and heats the gas. we show that the simulation sample of the cdm model without adding extra heating sources can fit well the observed distributions of x-ray luminosity versus temperature (lx vs. t) of galaxy groups and is also consistent with the distributions of x-ray luminosity versus velocity dispersion (lx vs. σ). because the baryonic gas is multiphase, the lx−t and lx−σ distributions are significantly scattered. if we describe the relationships by power laws lx ∝ t lt and lx ∝ σlv, we find αlt>2.5 and αlv>2.1. the x-ray background in the soft 0.5−2 kev band emitted by the baryonic gas in the temperature range 10550 ρdm is generally clustered and discretely distributed. therefore, almost all of the soft x-ray background comes from clustered sources, and the contribution from truly diffuse gas is probably negligible. this point agrees with current x-ray observations.

weak lensing measurements are starting to provide statistical maps of the distribution of matter in the universe that are increasingly precise and complementary to cosmic microwave background maps. the probability distribution (pdf) provides a powerful tool to test non-gaussian features in the convergence field and to discriminate the different cosmological models. in this letter, we present a new pdf space wiener filter approach to reconstruct the probability density function of the convergence from the noisy convergence field. we find that for parameters comparable to the cfht legacy survey, the averaged pdf of the convergence in a 3 degree field can be reconstructed with an uncertainty of about 10%, even though the pointwise pdf is noise dominated.

the statistics of gravitational lensing can provide us with a very powerful probe of the mass distribution of matter in the universe. by comparing predicted strong lensing probabilities with observations, we can test the mass distribution of dark matter halos, in particular, the inner density slope. in this letter, unlike previous work that directly models the density profiles of dark matter halos semi-analytically, we generalize the density profiles of dark matter halos from high-resolution n-body simulations by means of generalized navarro-frenk-white (gnfw) models of three populations with slopes, α, of about -1.5, -1.3 and -1.1 for galaxies, groups and clusters, respectively. this approach is an alternative and independent way to examine the slopes of mass density profiles of halos. we present calculations of lensing probabilities using these gnfw profiles for three populations in various spatially flat cosmological models with a cosmological constant. it is shown that the compound model of density profiles does not match well with the observed lensing probabilities derived from the jodrell-bank vla astrometric survey data in combination with the cosmic lens all-sky survey data. together with the previous work on lensing probability, our results suggest that a singular isothermal sphere mass model of less than about 1013h−1m⊙ can predict strong lensing probabilities that are consistent with observations of small splitting angles.

weak lensing measurements are starting to provide statistical maps of the distribution of matter in the universe that are increasingly precise and complementary to cosmic microwave background maps. the most common measurement is the correlation in alignments of background galaxies which can be used to infer the variance of the projected surface density of matter. this measurement of the fluctuations is insensitive to the total mass content and is analogous to using waves on the ocean to measure its depths. however, when the depth is shallow as happens near a beach waves become skewed. similarly, a measurement of skewness in the projected matter distribution directly measures the total matter content of the universe. while skewness has already been convincingly detected, its constraint on cosmology is still weak. we address optimal analyses for the cfht legacy survey in the presence of noise. we show that a compensated gaussian filter with a width of 2.5 arc minutes optimizes the cosmological constraint, yielding m/m 10%. this is significantly better than other filters which have been considered in the literature. this can be further improved with tomography and other sophisticated analyses.

weak gravitational lensing provides a direct statistical measure of the dark matter distribution. the variance is easiest to measure, which constrains the degenerate product 8 0.6 0. the degeneracy is broken by measuring the skewness arising from the fact that densities must remain positive, which is not possible when the initially symmetric perturbations become non-linear. skewness measures the non-linear mass scale, which in combination with the variance measures 0 directly. we present the first detection of dark matter skewness from the virmos-decart survey. we have measured the full three point function, and its projections onto windowed skewness. we separate the lensing mode and the b mode. the lensing skewness is detected for a compensated gaussian on scales of 5.37 arc minutes to be k-3=1.06±0.06×10−6. the b-modes are consistent with zero at this scale. the variance for the same window function is k-2=5.32±0.62±0.98×10−5, resulting in s3=375 342−124. comparing to n-body simulations, we find 0<0.5 at 90% confidence. the canada-france-hawaii-telescope legacy survey and newer simulations should be able to improve significantly on the constraint.