In this paper, we used standard rulers and standard candles(separately and jointly) to explore five popular dark energy models under the assumption of the spatial flatness of the Universe. As standard rulers, we used a data set comprised of 118 galactic scale strong lensing systems(individual standard rulers if properly calibrated for the mass density profile) combined with BAO diagnostics(statistical standard ruler). Type Ia supernovae served as standard candles. Unlike most previous statistical studies involving strong lensing systems, we relaxed the assumption of a singular isothermal sphere(SIS) in favor of its generalization: the power-law mass density profile. Therefore, along with cosmological model parameters,we fitted the power law index and its first derivative with respect to the redshift(thus allowing for mass density profile evolution). It turned out that the best fitted γ parameters are in agreement with each other,irrespective of the cosmological model considered. This demonstrates that galactic strong lensing systems may provide a complementary probe to test the properties of dark energy. The fits for cosmological model parameters which we obtained are in agreement with alternative studies performed by other researchers.Because standard rulers and standard candles have different parameter degeneracies, a combination of standard rulers and standard candles gives much more restrictive results for cosmological parameters. Finally,we attempted an analysis based on model selection using information theoretic criteria(AIC and BIC). Our results support the claim that the cosmological constant model is still best and there is no(at least statistical)reason to prefer any other more complex model.
We explore the problems of degeneracy and discreteness in the standard cosmological model(ΛCDM). We use the Observational Hubble Data(OHD) and the type Ia supernovae(SNe Ia) data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.
A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole(BH) is proposed.In the diskcorona scenario,we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations.The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere.It is shown that jet power increases with the increasing BH spin,and concentrates in the inner region of the disk-corona.In addition,we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism,and show that our jet formation mechanism can simulate almost all sources with high power jet,which fails to be explained by the Blandford-Znajek(BZ) process.
We present a multi-wavelength study of the gravitational lens COSMOS J095930+023427 (z l=0.892),together with the associated galaxy group along the line of sight located at z ～ 0.7,and the lensed background galaxy.The source redshift is currently unknown,but estimated to be at z s ～ 2.This analysis is based on publicly available HST,Subaru and Chandra imaging data,as well as VLT spectroscopy.The lensing system is an early-type galaxy showing a strong [OII] emission line,and produces four bright images of the distant background source.It has an Einstein radius of 0.79,about four times larger than the effective radius.We perform a lensing analysis using both a singular isothermal ellipsoid and a peudo-isothermal elliptical mass distribution for the lensing galaxy,and find that the final results on the total mass,the dark matter (DM) fraction within the Einstein radius and the external shear due to a foreground galaxy group are robust with respect to the choice of the parametric model and the source redshift (yet unknown).We measure the luminous mass from the photometric data,and find the DM fraction within the Einstein radius f DM to be between 0.71 ± 0.13 and 0.79 ± 0.15,depending on the unknown source redshift.Meanwhile,the non-null external shear found in our lensing models supports the presence and structure of a galaxy group at z ～ 0.7,and an independent measurement of the 0.5-2 keV X-ray luminosity within 20 around the X-ray centroid provides a group mass of M=(3 10) × 10 13 M,in good agreement with the previous estimate derived through weak lensing analysis.Finally,by inverting the HST/ACS I 814 image with the lensing equation,we obtain the reconstructed image of the magnified source galaxy,which has a scale of about 3.3 kpc at z s=2 (2.7 kpc at z s=4) and the typical disturbed disk-like appearance observed in low-mass star-forming galaxies at z ～ 3.However,deep,spatially resolved spectroscopic data for similar lensed sources are still required to detect the first stage of galaxy evolution,since t
We use the latest data to investigate observational constraints on the new generalized Chaplygin gas(NGCG) model.Using the Markov Chain Monte Carlo method,we constrain the NGCG model with type Ia supernovae from the Union2 set(557 data),the usual baryonic acoustic oscillation(BAO) observation from the spectroscopic Sloan Digital Sky Survey data release 7 galaxy sample,the cosmic microwave background observation from the 7-year Wilkinson Microwave Anisotropy Probe results,newly revised data on H(z),as well as a value of θBAO(z=0.55)=(3.90°±0.38°) for the angular BAO scale.The constraint results for the NGCG model are ωX=-1.0510-0.1685+0.1563(1σ)-0.2398+0.2226(2σ),η=1.0117-0.0502+0.0469(1σ)-0.0716+0.0693(2σ) and ΩX=0.7297-0.0276+0.0229(1σ)-0.0402+0.0329(2σ),which give a rather stringent constraint.From the results,we can see that a phantom model is slightly favored and the probability that energy transfers from dark matter to dark energy is a little larger than the inverse.
