Multivariate Predictors of Lyman Continuum Escape. I. A Survival Analysis of the Low-redshift Lyman Continuum Survey
Ferguson, Henry C.; Giavalisco, Mauro; Pentericci, Laura; Verhamme, Anne; Scarlata, Claudia; Henry, Alaina; Hayes, Matthew; Jaskot, Anne E.; Silveyra, Anneliese C.; Plantinga, Anna; Flury, Sophia R.; Chisholm, John; Heckman, Timothy; Schaerer, Daniel; Trebitsch, Maxime; Carr, Cody; Ji, Zhiyuan; Marques-Chaves, Rui; Östlin, Göran; Saldana-Lopez, Alberto; Worseck, Gábor; Xu, Xinfeng
United States, Sweden, Italy, Switzerland, Netherlands, France, China, Germany
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 (ΣSFR) 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, ΣSFR, and [O III]/[O II]. We find that ΣSFR 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 Lyα escape fraction. These multivariate models represent a promising tool for predicting f esc at high redshift. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-15626, GO-13744, GO-14635, GO-15341, and GO-15639.