Cosmological constraints from the small scale clustering of Emission Line Galaxies

TL;DR

This study demonstrates that analyzing small-scale clustering of Emission Line Galaxies from DESI can yield precise cosmological constraints, even with minimal survey volume, by extending into the nonlinear regime.

Contribution

The paper introduces a modified Subhalo Abundance Matching method for ELGs and validates it with simulations, enabling unbiased cosmological constraints from nonlinear scales.

Findings

Achieved ~6% constraints on σ₈ and Ωₘh² from 1% of DESI data.

Including scales below 0.8 h⁻¹ Mpc is essential for unbiased results.

Full survey could significantly improve precision using nonlinear clustering.

Abstract

Spectroscopic surveys such as the Dark Energy Spectroscopic Instrument (DESI) and Euclid are mapping the spatial distribution of millions of galaxies, with Emission Line Galaxies (ELGs) serving as the dominant tracer in the redshift range $0.8<z<1.6$. Standard approaches for extracting cosmological information from galaxy clustering, however, typically discard highly constraining measurements from the nonlinear regime. We apply SHAMe-SF - a modification of Subhalo Abundance Matching tailored for star-forming galaxy samples - to analyse the three-dimensional clustering of DESI ELGs from the One-Percent data release, extending their cosmological analysis deep into the nonlinear regime. We validate our pipeline using two mock ELG samples drawn from the state-of-the-art cosmological hydrodynamical simulation MillenniumTNG, demonstrating that our model yields unbiased constraints on $\sigma_8$ and $\Omega_{\rm m}h^2$ down to scales of $0.3~h^{-1}$Mpc on both samples. We find that including scales below $0.8~h^{-1}$Mpc is critical for mitigating projection effects and obtaining unbiased constraints on $\sigma_8$. Applied to the DESI One-Percent measurements, our analysis yields $\sim6$% constraints on $\sigma_8 = 0.81^{+0.05}_{-0.06}$ and $\Omega_{\rm m}h^2=0.146^{+0.009}_{-0.009}$. Remarkably, the accuracy of these constraints is similar to that obtained from the combined full-shape analysis of all DESI DR1 tracers, yet using only 1% of the survey volume. A naive extrapolation of our results from the One-Percent to the full survey area suggests that the complete survey could deliver roughly an order-of-magnitude improvement in precision - a prospect that, while subject to significant practical challenges, illustrates the cosmological potential encoded in the nonlinear regime.