Constraints on Baryon Density from the Effective Optical Depth of High-Redshift Quasars

Abstract

We present constraints on the baryonic matter density parameter, ${\Omega }_b$, within the framework of the $\Lambda$CDM model. Our analysis utilizes observational data on the effective optical depth from high-redshift quasars. To parameterize the photoionization rate ${\Gamma }_{-12}$, we employ a Bézier polynomial. Additionally, we approximate the Hubble parameter at high redshifts as $H(z)\approx 100h{\Omega }_m^{1/2}(1+z{)}^{3/2}$ km s${}^{-1}$ Mpc${}^{-1}$. Confidence regions are obtained with $h=0.701\pm 0.013$ and ${\Omega }_m=0.315$, optimized by the Planck mission. The best-fit values are ${\Omega }_b=0.043_{-0.006}^{+0.005}$ and ${\Omega }_b=0.045_{-0.006}^{+0.004}$, corresponding to an old data set and a new data set, respectively. And we test the non-parametric form of ${\Gamma }_{-12}$, obtaining ${\Omega }_b=0.048_{-0.003}^{+0.001}$. These results are consistent with the findings of Planck at the 1 $\sigma$ confidence level. Our findings underscore the effectiveness of quasar datasets in constraining ${\Omega }_b$, eliminating the need for independent photoionization rate data. This approach provides detailed cosmic information about baryon density and the photoionization history of the intergalactic medium.

arXiv comment14 pages, 10 figures, accepted by Research in Astronomy and Astrophysics (RAA)