Predicting LyC emission of galaxies using their physical and Lyα emission properties

Moupiya Maji , Anne Verhamme (1) , Joakim A Rosdahl (1) , Thibault Garel (1) , Jérémy Blaizot (1) , Valentin Mauerhofer (1) , Marta Pittavino , Maria-Pia Victoria Feser , Mathieu Chuniaud (1) , Taysun Kimm (2) , Harley Katz (3) , Martin Haehnelt (4)

1 CRAL - Centre de Recherche Astrophysique de Lyon
2 Yonsei University
3 University of Oxford
4 CAM - University of Cambridge [UK]

Aims. The primary difficulty in understanding the sources and processes that powered cosmic reionization is that it is not possible to directly probe the ionizing Lyman Continuum (LyC) radiation at that epoch as those photons have been absorbed by the intervening neutral hydrogen. It is therefore imperative to build a model to accurately predict LyC emission using other properties of galaxies in the reionization era. Methods. In recent years, studies have shown that the LyC emission from galaxies may be correlated to their Lyman-alpha (Lyα) emission. In this paper we study this correlation by analyzing thousands of simulated galaxies at high redshift in the SPHINX cosmological simulation. We post-process these galaxies with the Lyα radiative transfer code RASCAS and analyze the Lyα-LyC connection. Results. We find that the Lyα and LyC luminosities are strongly correlated with each other, although with dispersion. There is a positive correlation between the escape fractions of Lyα and LyC radiations in the brightest Lyα emitters (escaping Lyα luminosity L Lyα esc > 10 41 erg/s), similar to that reported by recent observational studies. However, when we also include fainter Lyα emitters (LAEs), the correlation disappears, which suggests that the observed relation may be driven by selection effects. We also find that the brighter LAEs are dominant contributors to reionization, with L Lyα esc > 10 40 erg/s galaxies accounting for > 90% of the total amount of LyC radiation escaping into the inter-galactic medium in the simulation. Finally, we build predictive models using multivariate linear regression where we use the physical and the Lyα properties of simulated reionization era galaxies to predict their LyC emission. We build a set of models using different sets of galaxy properties as input parameters and predict their intrinsic and escaping LyC luminosity with a high degree of accuracy (adjusted R 2 of these predictions in our fiducial model are 0.89 and 0.85 respectively, where R 2 is a measure of how much of the response variance is explained by the model). We find that the most important galaxy properties to predict the escaping LyC luminosity of a galaxy are its L Lyα esc , gas mass, gas metallicity and star formation rate. Conclusions. These results and the predictive models can be useful to predict the LyC emission from galaxies using their physical and Lyα properties and thus help us identify the sources of reionization.

Domaines: Astrophysique [astro-ph]

Moupiya Maji, Anne Verhamme, Joakim A Rosdahl, Thibault Garel, Jérémy Blaizot, et al.. Predicting LyC emission of galaxies using their physical and Lyα emission properties. Astronomy and Astrophysics - A&A, 2022, 663, pp.A66. ⟨10.1051/0004-6361/202142740⟩. ⟨insu-03777343v1⟩