Constraints on the cosmic expansion rate at redshift 2.3 from the Lyman-$\alpha$ forest

Understand

We determine the product of the expansion rate and angular-diameter distance at redshift $z=2.3$ from the anisotropy of Lyman-$\alpha$ (Ly$\alpha$) forest correlations measured by the Sloan Digital Sky Survey (SDSS).

• Our result is the most precise from large-scale structure at $z>1$.
• In flat $\Lambda$CDM we determine the matter density to be $\Omega_\mathrm{m}=0.36^{+0.03}_{-0.04}$ from Ly$\alpha$ alone.
• This is a factor of two tighter than baryon acoustic oscillation results from the same data due to our use of a wide range of scales ($25<r<180$ $h^{-1}\text{Mpc}$).