Constraints on the dark energy equation of state from recent supernova data

Measurements suggest that our universe has a substantial dark energy component. The most recent data on type Ia supernovae give a dark energy density which is in good agreement with other measurements if the dark energy is assumed to be a cosmological constant. Here we examine to what extent that data can put constraints on a more general equation of state for the dark energy.

Figure 1

In the left panel, the 68.3%, 90%, 95.4%, and 99.7% confidence contours for the gold data fit with a cosmological constant are shown. The cross indicates the best fit, and the solid circle the best fit to a flat cosmology. The right panel shows the 68.3%, 90%, and the 95.4% confidence contours for the data in Ref. 1.

Figure 2

The ${\chi }^2$ variation of the parameters ${\Omega }_M$, ${\Omega }_X$, $w_0$, and $w_1$ is shown for the cases $w(z)=w_0+w_{1}z/(1+z)$ (solid line) and $w(z)=w_0+w_{1}z$ (dashed line). The horizontal lines correspond to $\Delta {\chi }^2=1$.

Figure 3

Same as Fig. 2 except that ${\Omega }_X=1-{\Omega }_M$.

Figure 4

The 68.3%, 90%, 95.4%, and 99.7% confidence contours for the case ${\Omega }_X=1-{\Omega }_M$ and $p_x=w_0{\rho }_x$ (Model V) are shown. The cross indicates the best fit, and the solid circle is the fit requiring ${\Omega }_M=0.3$. The dashed line separates accelerating (to the left) from decelerating (to the right) cosmologies.