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 105<T<107K has also been calculated. We show that of the total background, (1) no more than 2% comes from the region with temperature less than 106.5 K, and (2) no more than 7% is from the region of dark matter with mass density ρdm<50 ρdm. The region of ρdm>50 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.

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.

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.

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.