Four new observational<i>H</i>(<i>z</i>) data from luminous red galaxies in the Sloan Digital Sky Survey data release seven

Abstract

By adopting the differential age method, we utilize selected 17832 luminous\nred galaxies (LRGs) from Sloan Digital Sky Survey Data Release Seven (SDSS DR7)\ncovering redshift $0&lt;z&lt;0.4$ to measure Hubble parameters. Using a full spectrum\nfitting package UlySS, these spectra are reduced with single stellar population\n(SSP) models and optimal age information of our selected sample are derived.\nWith the decreasing age-redshift relation, four new observational $H(z)$ data\n(OHD) points are obtained, which are $H(z)=69.0\\pm19.6$ km s$^{-1}$ Mpc$^{-1}$\nat $z=0.07$, $H(z)=68.6\\pm26.2$ km s$^{-1}$ Mpc$^{-1}$ at $z=0.12$,\n$H(z)$=$72.9\\pm29.6$ km s$^{-1}$ Mpc$^{-1}$ at $z=0.2$ and $H(z)$=$88.8\\pm36.6$\nkm s$^{-1}$ Mpc$^{-1}$ at $z=0.28$, respectively. Combined with other 21\navailable OHD data points, a performance of constraint on both flat and\nnon-flat $\\Lambda$CDM model is presented.\n