In a semi-numerical model of reionization, the evolution of ionization fraction is approximately simulated by the criterion of ionizing photon to baryon ratio. We incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semianalytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-z observations, and it also fits the high redshift luminosity function reasonably well, but its prediction about star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization cannot be completed at z ～ 6. We also consider simple modifications of the model with more top heavy initial mass functions, which can allow the reionization to occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the epoch of reionization, and the neutral regions produced by our simulations with the semi-analytical model, which appeared less poriferous than the simple halo-based models.
Jie ZhouQi GuoGao-Chao LiuBin YueYi-Dong XuXue-Lei Chen
Combining the latest Planck,Wilkinson Microwave Anisotropy Probe(WMAP),and baryon acoustic oscillation(BAO)data,we exploit the recent cosmic microwave background(CMB)B-mode power spectra data released by the BICEP2 collaboration to constrain the cosmological parameters of the ACDM model,especially the primordial power spectra parameters of the scalar and the tensor modes,ns,s,r,nt.We obtain constraints on the parameters for a lensed ACDM model using the Markov Chain Monte Carlo(MCMC)technique,the marginalized 68%bounds are r=0.03070.09140.1043,ns=0.00610.00610.9617,s=0.01050.00970.0175,nt=0.45150.45790.5198.We find that a blue tilt for nt is favored slightly,but it is still well consistent with flat or even red tilt.Our r value is slightly smaller than the one obtained by the BICEP group,in that we permit nt as a free parameter without imposing the single-field slow roll inflation consistency relation.When we impose this relation,then r=0.04460.06090.2130.For most other parameters,the best fit values and measurement errors are not altered significantly by the introduction of the BICEP2 data.
We apply our sky map reconstruction method for transit type interferometers to the Tianlai cylinder array.The method is based on spherical harmonic decomposition,and can be applied to a cylindrical array as well as dish arrays and we can compute the instrument response,synthesized beam,transfer function and noise power spectrum.We consider cylinder arrays with feed spacing larger than half a wavelength and,as expected,we find that the arrays with regular spacing have grating lobes which produce spurious images in the reconstructed maps.We show that this problem can be overcome using arrays with a different feed spacing on each cylinder.We present the reconstructed maps,and study the performance in terms of noise power spectrum,transfer function and beams for both regular and irregular feed spacing configurations.
