Probing the course of cosmic expansion with a combination of observational data

Abstract

We study the cosmic expansion history by reconstructing thedeceleration parameter q(z) from the SDSS-II type Ia supernovasample (SNIa) with two different light curve fits (MLCS2k2 andSALT-II), the baryon acoustic oscillation (BAO) distance ratio, thecosmic microwave background (CMB) shift parameter, and the lookbacktime-redshift (LT) from the age of old passive galaxies. Threeparametrization forms for the equation of state of dark energy (CPL,JBP, and UIS) are considered. Our results show that, for the CPL andthe UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-IISNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration,but this does not occur for all other cases, where an increasingcosmic acceleration is still favored. Thus, the reconstructedevolutionary behaviors of dark energy and the course of the cosmicacceleration are highly dependent both on the light curve fittingmethod for the SNIa and the parametrization form for the equation ofstate of dark energy.