First Cosmological Constraints on Dark Energy from the Radial Baryon Acoustic Scale

We present cosmological constraints arising from the first measurement of the radial (line-of-sight) baryon acoustic oscillations (BAO) scale in the large scale structure traced by the galaxy distribution. Here we use these radial BAO measurements at $z=0.24$ and $z=0.43$ to derive new constraints on dark energy and its equation of state for a flat universe, without any other assumptions on the cosmological model: $w=-1.14\pm 0.39$ (assumed constant), ${\Omega }_m={0.24}_{-0.05}^{+0.06}$. If we drop the assumption of flatness and include previous cosmic microwave background and supernova data, we find $w=-0.974\pm 0.058$, ${\Omega }_m=0.271\pm 0.015$, and ${\Omega }_k=-0.002\pm 0.006$, in good agreement with a flat cold dark matter cosmology with a cosmological constant. To our knowledge, these are the most stringent constraints on these parameters to date under our stated assumptions.

Figure 1

The 68% C.L. constraints on the plane ${\Omega }_m\mathrm{\text{−}}w$ when a flat universe is assumed. In yellow, from the measurements of the RBAO scale plus ${\Omega }_b{h}^2$ and ${\Omega }_m{h}^2$. In pink, from RBAO plus $l_A$ and $z^{*}$ from WMAP5 [1] In blue, from the RBAO scale plus WMAP5, and in red, from the RBAO scale, plus WMAP5 plus supernovae [18]. Results are consistent among them and compatible with a $\Lambda \mathrm{CDM}$ cosmology.

Figure 2

The 68% C.L. constraints on the plane ${\Omega }_m\mathrm{\text{−}}w$ when a nonflat constant-$w$ cosmology is assumed. In blue, from the RBAO scale plus WMAP5 [1], and in red, from the RBAO scale plus WMAP5 plus supernovae [18]. Results are consistent with a cosmological constant universe with a precision around 5%.