A Multi-Fidelity Emulator for the Lyman-$\alpha$ Forest Flux Power Spectrum

TL;DR

This paper develops a multi-fidelity emulation method for the Lyman-alpha forest flux power spectrum, combining cheap low-fidelity and expensive high-fidelity simulations to accurately interpolate cosmological data.

Contribution

It extends multi-fidelity emulation techniques to the Lyman-alpha forest, improving accuracy and enabling exploration of smaller scales and higher redshifts.

Findings

Achieves 0.8% accuracy in reproducing the flux power spectrum

Outperforms single-fidelity emulators in accuracy

Enables extension of simulations to smaller scales and higher redshifts

Abstract

In this work we extend our recently developed multi-fidelity emulation technique to the simulated Lyman-$\alpha$ forest flux power spectrum. Multi-fidelity emulation allows interpolation of simulation outputs between cosmological parameters using many cheap low-fidelity simulations and a few expensive high-fidelity simulations. Using a test suite of small box (30 Mpc/h) simulations, we show that multi-fidelity emulation is able to reproduce the Lyman-$\alpha$ forest flux power spectrum well, achieving an average accuracy when compared to a test suite of $0.8\%$. We further show that it has a substantially increased accuracy over single-fidelity emulators, constructed using either the high or low-fidelity simulations only. In particular, it allows the extension of an existing simulation suite to smaller scales and higher redshifts.