Globalemu: a novel and robust approach for emulating the sky-averaged 21-cm signal from the cosmic dawn and epoch of reionization. Issue 2 (25th September 2021)

• Record Type: Journal Article
• Authors: Bevins, H T J; Handley, W J; Fialkov, A; de Lera Acedo, E; Javid, K
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 508:Issue 2(2021)
• Page Start: 2923
• Page End: 2936
• Publication Date: 2021-09-25
• Subjects: early Universe -- reionization -- first stars -- dark ages -- software: data analysis -- software: simulations; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab2737
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Emulation of the Global (sky-averaged) 21-cm signal with neural networks has been shown to be an essential tool for physical signal modelling. In this paper, we present globalemu, a Global 21-cm signal emulator that uses redshift as a character-defining variable alongside a set of astrophysical parameters to estimate the signal brightness temperature. Combined with physically motivated data pre-processing, this makes for a reliable and fast emulator that is relatively insensitive to the network design. globalemu can emulate a high-resolution signal in 1.3 ms in comparison to 133 ms, a factor of 102 improvement, when using the existing public state-of-the-art 21cmGEM . We illustrate, with the standard astrophysical models used to train 21cmGEM, that globalemu is almost twice as accurate and for a test set of ≈1700 signals we achieve a mean root mean squared error of 2.52 mK across the band z = 7–28 [≈10 per cent the expected noise of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH)]. The models are parametrized by the star formation efficiency, f *, minimum virial circular velocity, V c, X-ray efficiency, f X, cosmic microwave background optical depth, τ, the slope and low energy cut-off of the X-ray spectral energy density, α and ν min, respectively, and the mean free path of ionizing photons, R mfp . globalemu provides a flexible framework for easily emulating updated simulations of the Global signal and in addition the neutral fraction history. The emulator is pip installable and available at https://github.com/htjb/globalemu . globalemu will be used extensively by the REACH collaboration.