Predicting Ly$\alpha$ Emission from Distant Galaxies with Neural Network Architecture

Abstract

The Ly$\alpha$ emission line is a characteristic feature found in high-$z$ galaxies, serving as a probe of cosmic reionization. While previous works present various correlations between Ly$\alpha$ emission and physical properties of host galaxies, it is still unclear which characteristics predominantly determine the Ly$\alpha$ emission. In this study, we introduce a neural network approach to simultaneously handle multiple properties of galaxies. The neural-network-based prediction model that identifies Ly$\alpha$ emitters (LAEs) from six physical properties: star formation rate (SFR), stellar mass, UV absolute magnitude $M_\mathrm{UV}$, age, UV slope $\beta$, and dust attenuation $E(B-V)$, obtained by the SED fitting. The network is trained with galaxy samples from the VANDELS and MUSE spectroscopic surveys and achieves the performance of 77% true positive rate and 14% false positive rate. The permutation feature importance method shows that $\beta$, $M_\mathrm{UV}$, and $M_*$ are important for the prediction of LAEs. As an independent validation, we find that 91% of LAEs spectroscopically confirmed by the James Webb Space Telescope (JWST) have a probability of LAE higher than 70% in this model. This prediction model enables the efficient construction of a large LAE sample in a wide and continuous redshift space using only photometric data. We apply the prediction model to the JWST photometric galaxy sample and obtain Ly$\alpha$ fraction consistent with previous studies. Moreover, we demonstrate that the difference between the distributions of LAEs predicted by the model and the spectroscopically identified LAEs provides a strong constraint on the HII bubble size.