The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium

Partly based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 280.D-5059, 081.A-0856, 082.A-0301, 083.A-0644, 091.A-0442, 100.D-0649, and 102.D-0662. Partly based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias, under programs 31-014, 32-010, 39-023, 48-005, and 51-504. Partly based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofśica de Canarias, in the island of La Palma, Spain. Partly based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, under programs A26TAC_63 and A32TAC_5. The WHT and its override programme (for 090715B: programme W09AN001, P.I. Curran; for 161017A: programme W/2017A/23, P.I. Levan) are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. We thank A. Kamble, R. Starling, and P. Curran for their help with the 090715B observations, and Marie Hrudkova for executing the 161017A observations. Partly based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). Partially