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

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.

12 pages, 10 figures

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• Possible evidence for a large-scale enhancement in the Lyman-$\alpha$ forest power spectrum at redshift $\text{z}\ge 4$