Multivariate Predictors of Lyman Continuum Escape. I. A Survival Analysis of the Low-redshift Lyman Continuum Survey

Abstract

To understand how galaxies reionized the Universe, we must determine how the escape fraction of Lyman continuum (LyC) photons ( f _esc ) depends on galaxy properties. Using the z ∼ 0.3 Low-redshift Lyman Continuum Survey (LzLCS), we develop and analyze new multivariate predictors of f _esc . These predictions use the Cox proportional hazards model, a survival analysis technique that incorporates both detections and upper limits. Our best model predicts the LzLCS f _esc detections with an rms scatter of 0.31 dex, better than single-variable correlations. According to ranking techniques, the most important predictors of f _esc are the equivalent width (EW) of Lyman-series absorption lines and the UV dust attenuation, which track line-of-sight absorption due to H i and dust. The H i absorption EW is uniquely crucial for predicting f _esc for the strongest LyC emitters, which show properties similar to weaker LyC emitters and whose high f _esc may therefore result from favorable orientation. In the absence of H i information, star formation rate surface density (Σ _SFR ) and [O iii ]/[O ii ] ratio are the most predictive variables and highlight the connection between feedback and f _esc . We generate a model suitable for z > 6, which uses only the UV slope, Σ _SFR , and [O iii ]/[O ii ]. We find that Σ _SFR is more important in predicting f _esc at higher stellar masses, whereas [O iii ]/[O ii ] plays a greater role at lower masses. We also analyze predictions for other parameters, such as the ionizing-to-nonionizing flux ratio and Ly α escape fraction. These multivariate models represent a promising tool for predicting f _esc at high redshift.

Keywords

• Astrostatistics
• Reionization
• High-redshift galaxies
• Starburst galaxies
• Interstellar medium
• Ultraviolet astronomy