{"oa_version":"Published Version","main_file_link":[{"open_access":"1","url":"https://arxiv.org/abs/1803.08923"}],"title":"Predicting Lyα escape fractions with a simple observable: Lyα in emission as an empirically calibrated star formation rate indicator","quality_controlled":"1","scopus_import":"1","intvolume":"       623","language":[{"iso":"eng"}],"date_published":"2019-03-26T00:00:00Z","year":"2019","article_type":"original","publisher":"EDP Sciences","day":"26","keyword":["Space and Planetary Science","Astronomy and Astrophysics","galaxies: high-redshift / galaxies: star formation / galaxies: statistics / galaxies: evolution / galaxies: formation / galaxies: ISM"],"publication":"Astronomy & Astrophysics","publication_status":"published","abstract":[{"text":"Lyman-α (Lyα) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lyα luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars (M⋆ ≳ 10 M⊙) with lifetimes of a few Myrs. As such, Lyα luminosity should be an excellent instantaneous star formation rate (SFR) indicator. However, its resonant nature and susceptibility to dust as a rest-frame UV photon makes Lyα very hard to interpret due to the uncertain Lyα escape fraction, fesc, Lyα. Here we explore results from the CAlibrating LYMan-α with Hα (CALYMHA) survey at z = 2.2, follow-up of Lyα emitters (LAEs) at z = 2.2 − 2.6 and a z ∼ 0−0.3 compilation of LAEs to directly measure fesc, Lyα with Hα. We derive a simple empirical relation that robustly retrieves fesc, Lyα as a function of Lyα rest-frame EW (EW0): fesc,Lyα = 0.0048 EW0[Å] ± 0.05 and we show that it constrains a well-defined anti-correlation between ionisation efficiency (ξion) and dust extinction in LAEs. Observed Lyα luminosities and EW0 are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lyα and LyC luminosities under well controlled and simple assumptions. Our results allow observed Lyα luminosities to be used to compute SFRs for LAEs at z ∼ 0−2.6 within ±0.2 dex of the Hα dust corrected SFRs. We apply our empirical SFR(Lyα,EW0) calibration to several sources at z ≥ 2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20 M⊙ yr−1 and that our calibration might be even applicable for the most luminous LAEs within the epoch of re-ionisation. Our results imply high ionisation efficiencies (log10[ξion/Hz erg−1] = 25.4−25.6) and low dust content in LAEs across cosmic time, and will be easily tested with future observations with JWST which can obtain Hα and Hβ measurements for high-redshift LAEs.","lang":"eng"}],"article_number":"A157","doi":"10.1051/0004-6361/201833075","author":[{"full_name":"Sobral, David","first_name":"David","last_name":"Sobral"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee"}],"_id":"11507","publication_identifier":{"eissn":["1432-0746"],"issn":["0004-6361"]},"volume":623,"date_updated":"2022-07-19T09:37:20Z","type":"journal_article","extern":"1","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","oa":1,"status":"public","external_id":{"arxiv":["1803.08923"]},"citation":{"ista":"Sobral D, Matthee JJ. 2019. Predicting Lyα escape fractions with a simple observable: Lyα in emission as an empirically calibrated star formation rate indicator. Astronomy &#38; Astrophysics. 623, A157.","chicago":"Sobral, David, and Jorryt J Matthee. “Predicting Lyα Escape Fractions with a Simple Observable: Lyα in Emission as an Empirically Calibrated Star Formation Rate Indicator.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2019. <a href=\"https://doi.org/10.1051/0004-6361/201833075\">https://doi.org/10.1051/0004-6361/201833075</a>.","apa":"Sobral, D., &#38; Matthee, J. J. (2019). Predicting Lyα escape fractions with a simple observable: Lyα in emission as an empirically calibrated star formation rate indicator. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/201833075\">https://doi.org/10.1051/0004-6361/201833075</a>","short":"D. Sobral, J.J. Matthee, Astronomy &#38; Astrophysics 623 (2019).","ama":"Sobral D, Matthee JJ. Predicting Lyα escape fractions with a simple observable: Lyα in emission as an empirically calibrated star formation rate indicator. <i>Astronomy &#38; Astrophysics</i>. 2019;623. doi:<a href=\"https://doi.org/10.1051/0004-6361/201833075\">10.1051/0004-6361/201833075</a>","mla":"Sobral, David, and Jorryt J. Matthee. “Predicting Lyα Escape Fractions with a Simple Observable: Lyα in Emission as an Empirically Calibrated Star Formation Rate Indicator.” <i>Astronomy &#38; Astrophysics</i>, vol. 623, A157, EDP Sciences, 2019, doi:<a href=\"https://doi.org/10.1051/0004-6361/201833075\">10.1051/0004-6361/201833075</a>.","ieee":"D. Sobral and J. J. Matthee, “Predicting Lyα escape fractions with a simple observable: Lyα in emission as an empirically calibrated star formation rate indicator,” <i>Astronomy &#38; Astrophysics</i>, vol. 623. EDP Sciences, 2019."},"date_created":"2022-07-06T11:08:16Z","month":"03","article_processing_charge":"No","acknowledgement":"We thank the anonymous referees for multiple comments and suggestions which have improved the manuscript. JM acknowledges the support of a Huygens PhD fellowship from Leiden University. We have benefited greatly from the publicly available programming language PYTHON, including the NUMPY & SCIPY (Van Der Walt et al. 2011; Jones et al. 2001), MATPLOTLIB (Hunter 2007) and ASTROPY (Astropy Collaboration 2013) packages, and the TOPCAT analysis program (Taylor 2013). The results and samples of LAEs used for this paper are publicly available (see e.g. Sobral et al. 2017, 2018a) and we also provide the toy model used as a PYTHON script."}