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    Rights statement: © ESO 2019 Published version at https://doi.org/10.1051/0004-6361/201833075

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Predicting Lyman-alpha escape fractions with a simple observable: Lyman-alpha in emission as an empirically calibrated star formation rate indicator

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Predicting Lyman-alpha escape fractions with a simple observable : Lyman-alpha in emission as an empirically calibrated star formation rate indicator. / Sobral, David; Matthee, Jorryt.

In: Astronomy and Astrophysics, Vol. 623, A157, 31.03.2019.

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@article{ca120dc92aa3493aa33dd8f408de8add,
title = "Predicting Lyman-alpha escape fractions with a simple observable: Lyman-alpha in emission as an empirically calibrated star formation rate indicator",
abstract = "Lyman-alpha (Lya) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lya luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars with lifetimes of a few Myrs. As such, Lya 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 Lya very hard to interpret due to the uncertain Lya escape fraction, f$_{esc,Ly\alpha}$. Here we explore results from the CALYMHA survey at z=2.2, follow-up of Lya emitters (LAEs) at z=2.2-2.6 and a z~0-0.3 compilation of LAEs to directly measure f$_{esc,Ly\alpha}$ with H-alpha (Ha). We derive a simple empirical relation that robustly retrieves f$_{esc,Ly\alpha}$ as a function of Lya rest-frame EW (EW$_0$): f$_{esc,Ly\alpha}$= 0.0048 EW$_0[{\AA}]\pm0.05$ and we show that the relation is driven by a tight sequence between high ionisation efficiencies and low dust extinction in LAEs. Observed Lya luminosities and EW$_0$ are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lya and LyC luminosities under well controlled and simple assumptions. Our results allow observed Lya luminosities to be used to compute SFRs for LAEs at z~0-2.6 within 0.2 dex of the Ha dust corrected SFRs. We apply our empirical SFR(Lya,EW$_0$) calibration to several sources at z>2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20 M$_{\odot}$/yr and that our calibration might be even applicable for luminous LAEs within the epoch of re-ionisation. Our results imply higher than canonical ionisation efficiencies and low dust content in LAEs across cosmic time, and will be easily tested with future observations with JWST.",
keywords = "galaxies: high-redshift, galaxies: star formation, galaxies: evolution, galaxies: statistics, galaxies: formation, galaxies: ISM",
author = "David Sobral and Jorryt Matthee",
note = "{\textcopyright} ESO 2019 Published version at https://doi.org/10.1051/0004-6361/201833075",
year = "2019",
month = mar
day = "31",
doi = "10.1051/0004-6361/201833075",
language = "English",
volume = "623",
journal = "Astronomy and Astrophysics",
issn = "1432-0746",
publisher = "EDP Sciences",

}

RIS

TY - JOUR

T1 - Predicting Lyman-alpha escape fractions with a simple observable

T2 - Lyman-alpha in emission as an empirically calibrated star formation rate indicator

AU - Sobral, David

AU - Matthee, Jorryt

N1 - © ESO 2019 Published version at https://doi.org/10.1051/0004-6361/201833075

PY - 2019/3/31

Y1 - 2019/3/31

N2 - Lyman-alpha (Lya) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lya luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars with lifetimes of a few Myrs. As such, Lya 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 Lya very hard to interpret due to the uncertain Lya escape fraction, f$_{esc,Ly\alpha}$. Here we explore results from the CALYMHA survey at z=2.2, follow-up of Lya emitters (LAEs) at z=2.2-2.6 and a z~0-0.3 compilation of LAEs to directly measure f$_{esc,Ly\alpha}$ with H-alpha (Ha). We derive a simple empirical relation that robustly retrieves f$_{esc,Ly\alpha}$ as a function of Lya rest-frame EW (EW$_0$): f$_{esc,Ly\alpha}$= 0.0048 EW$_0[{\AA}]\pm0.05$ and we show that the relation is driven by a tight sequence between high ionisation efficiencies and low dust extinction in LAEs. Observed Lya luminosities and EW$_0$ are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lya and LyC luminosities under well controlled and simple assumptions. Our results allow observed Lya luminosities to be used to compute SFRs for LAEs at z~0-2.6 within 0.2 dex of the Ha dust corrected SFRs. We apply our empirical SFR(Lya,EW$_0$) calibration to several sources at z>2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20 M$_{\odot}$/yr and that our calibration might be even applicable for luminous LAEs within the epoch of re-ionisation. Our results imply higher than canonical ionisation efficiencies and low dust content in LAEs across cosmic time, and will be easily tested with future observations with JWST.

AB - Lyman-alpha (Lya) is intrinsically the brightest line emitted from active galaxies. While it originates from many physical processes, for star-forming galaxies the intrinsic Lya luminosity is a direct tracer of the Lyman-continuum (LyC) radiation produced by the most massive O- and early-type B-stars with lifetimes of a few Myrs. As such, Lya 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 Lya very hard to interpret due to the uncertain Lya escape fraction, f$_{esc,Ly\alpha}$. Here we explore results from the CALYMHA survey at z=2.2, follow-up of Lya emitters (LAEs) at z=2.2-2.6 and a z~0-0.3 compilation of LAEs to directly measure f$_{esc,Ly\alpha}$ with H-alpha (Ha). We derive a simple empirical relation that robustly retrieves f$_{esc,Ly\alpha}$ as a function of Lya rest-frame EW (EW$_0$): f$_{esc,Ly\alpha}$= 0.0048 EW$_0[{\AA}]\pm0.05$ and we show that the relation is driven by a tight sequence between high ionisation efficiencies and low dust extinction in LAEs. Observed Lya luminosities and EW$_0$ are easy measurable quantities at high redshift, thus making our relation a practical tool to estimate intrinsic Lya and LyC luminosities under well controlled and simple assumptions. Our results allow observed Lya luminosities to be used to compute SFRs for LAEs at z~0-2.6 within 0.2 dex of the Ha dust corrected SFRs. We apply our empirical SFR(Lya,EW$_0$) calibration to several sources at z>2.6 to find that star-forming LAEs have SFRs typically ranging from 0.1 to 20 M$_{\odot}$/yr and that our calibration might be even applicable for luminous LAEs within the epoch of re-ionisation. Our results imply higher than canonical ionisation efficiencies and low dust content in LAEs across cosmic time, and will be easily tested with future observations with JWST.

KW - galaxies: high-redshift

KW - galaxies: star formation

KW - galaxies: evolution

KW - galaxies: statistics

KW - galaxies: formation

KW - galaxies: ISM

U2 - 10.1051/0004-6361/201833075

DO - 10.1051/0004-6361/201833075

M3 - Journal article

VL - 623

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 1432-0746

M1 - A157

ER -