Figure 1

Left panel: deceleration parameter vs redshift. The shaded area shows the $1\sigma$ confidence region. Right panel: Hubble function vs redshift (the observational data are borrowed from Refs. 26, 27, 28, 29). In both panels the solid (red) and the dashed (green) lines are used for the best-fit of parametrization I [Eq. (11)] and for the $\Lambda \mathrm{CDM}$ model with ${\Omega }_{M0}=0.27$ and $H_0=72.1\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ (see Ref. 24), respectively. The latter graph is shown for comparison.Reuse & Permissions

Figure 2

Left panel: $1\sigma$ and $2\sigma$ confidence regions of the pair of free parameters ($q_1$, $q_2$) of parametrization I, Eq. (11). Right panel: $1\sigma$ and $2\sigma$ regions of the pair of free parameters ($H_0$, $q_0$). The dot signals the best-fit values.Reuse & Permissions

Figure 3

EoS parameters vs redshift. The shaded area shows the $1\sigma$ confidence region. The solid (red) and the dashed (green) lines are used for the best fit of parametrization I [Eq. (11)] and for the CPL parametrization Eq. (14), both with ${\Omega }_{M0}=0.27\pm 0.03$. For the CPL parametrization the values $w_0=-0.93\pm 0.12$ and $w_1=-{0.38}_{-0.65}^{+0.66}$ obtained by Komatsu et al. [24] were used.Reuse & Permissions

Figure 4

Same as Fig. 1 but for parametrization II, Eq. (15).Reuse & Permissions

Figure 5

Same as Fig. 2 but for parametrization II, Eq. (15).Reuse & Permissions

Figure 6

EoS parameters vs redshift. The shaded area shows the $1\sigma$ confidence region. The solid (red) and the dashed (green) lines are used for the best fit of parametrization I [Eq. (11)] and the CPL parametrization, Eq. (14), respectively, both assuming ${\Omega }_{M0}=0.27\pm 0.03$. For the CPL parametrization the values $w_0=-0.93\pm 0.12$ and $w_1=-{0.38}_{-0.65}^{+0.66}$ obtained by Komatsu et al. [24] were used.Reuse & Permissions

Figure 7

Same as Fig. 1 but for parametrization III, Eq. (16).Reuse & Permissions

Figure 8

Same as Fig. 2 but for parametrization III, Eq. (16).Reuse & Permissions

Figure 9

Deceleration parameters vs redshift. Solid (red), long dashed (blue) and short dashed (green) lines are for parameterizations I, II, and III, respectively. The graphs of parameterizations I and III practically overlap each other.Reuse & Permissions

Figure 10

Top panel: Observational constraints at $1\sigma$ confidence level on the deceleration parameter vs redshift obtained by Daly et al. using the combined sample 192 supernovae and 30 radio galaxies (top panel of Fig. 10 in Ref. 38); the thick solid line corresponds to the central experimental value of $q(z)$. Solid, dashed and dot-dashed lines correspond to parametrizations I [Eq. (11)], II [Eq. (15)] and III [Eq. (16)], respectively. Bottom panel: The same as the top panel except that the observational constraints on $q(z)$ were obtained solely from the sample of 30 radio galaxies (bottom panel of Fig. 10 in Ref. 38). In both panels parametrizations I and III practically overlap each other.Reuse & Permissions