Direction Dependence of the Deceleration Parameter

Abstract

In this paper we study the possibly existing anisotropy in the acceleration expansion by use of the full sample of Union2 data. Using the hemisphere comparison method to search for a preferred direction, we take the deceleration parameter q0 as the diagnostic to quantify the anisotropy level in the wCDM model. We find that the maximum accelerating expansion direction is $(l,b)=(314_{+20^{\circ}}^{\circ-13^{\circ}},28_{+11^{\circ}}^{\circ-33^{\circ}})$,with the maximum anisotropy level of $\delta q_{0,max}/\bar{q}_0=0.79_{+0.27}^{-0.28}$, and that the anisotropy is more prominent when only low redshift data ($z\leq0.2$) are used. We also discuss this issue in the $CPL$ parameterized model, showing a similar result.