摘要：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 Lyαluminosity 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, Lyαluminosity 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 Lyαvery hard to interpret due to the uncertain Lyαescape fraction,fesc, Lyα. Here we explore results from the CAlibrating LYMan-αwith Hα(CALYMHA) survey atz = 2.2, follow-up of Lyαemitters (LAEs) atz = 2.2 − 2.6 and az ∼ 0−0.3 compilation of LAEs to directly measurefesc, Lyαwith Hα. We derive a simple empirical relation that robustly retrievesfesc, Lyαas a function of Lyαrest-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 Lyαluminosities and EW0are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lyαand LyC luminosities under well controlled and simple assumptions. Our results allow observed Lyαluminosities to be used to compute SFRs for LAEs atz ∼ 0−2.6 within ±0.2 dex of the Hαdust corrected SFRs. We apply our empirical SFR(Lyα,EW0) calibration to several sources atz ≥ 2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20M⊙yr−1and 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 Hαand Hβmeasurements for high-redshift LAEs.
关键词：engalaxies: high-redshiftgalaxies: star formationgalaxies: statisticsgalaxies: evolutiongalaxies: formationgalaxies: ISM
