DESI DR1 Ly$\hat{I}\pm$ forest: 3D full-shape analysis and cosmological constraints

Abstract

We perform an analysis of the full shapes of Lyman-$\hat{I}\pm$ (Ly$\hat{I}\pm$) forest correlation functions measured from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI). Our analysis focuses on measuring the Alcock-Paczynski (AP) effect and the cosmic growth rate times the amplitude of matter fluctuations in spheres of $8$ $h^{-1}\text{Mpc}$, $f\ddot{I}{ƒ}_8$. We validate our measurements using two different sets of mocks, a series of data splits, and a large set of analysis variations, which were first performed blinded. Our analysis constrains the ratio $D_M/D_H(z_{\mathrm{eff}})=4.525\pm 0.071$, where $D_H=c/H(z)$ is the Hubble distance, $D_M$ is the transverse comoving distance, and the effective redshift is $z_{\mathrm{eff}}=2.33$. This is a factor of $2.4$ tighter than the Baryon Acoustic Oscillation (BAO) constraint from the same data. When combining with Ly$\hat{I}\pm$ BAO constraints from DESI DR2, we obtain the ratios $D_H(z_{\mathrm{eff}})/r_d=8.646\pm 0.077$ and $D_M(z_{\mathrm{eff}})/r_d=38.90\pm 0.38$, where $r_d$ is the sound horizon at the drag epoch. We also measure $f\ddot{I}{ƒ}_8(z_{\mathrm{eff}})=0.37{}_{-0.065}^{+0.055}(\mathrm{stat})\pm 0.033(\mathrm{sys})$, but we do not use it for cosmological inference due to difficulties in its validation with mocks. In $\hat{I}›$CDM, our measurements are consistent with both cosmic microwave background (CMB) and galaxy clustering constraints. Using a nucleosynthesis prior but no CMB anisotropy information, we measure the Hubble constant to be $H_0=68.3\pm 1.6\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$ within $\hat{I}›$CDM. Finally, we show that Ly$\hat{I}\pm$ forest AP measurements can help improve constraints on the dark energy equation of state, and are expected to play an important role in upcoming DESI analyses.