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Lyα emitters with very large Lyα equivalent widths, EW0(Lyα) ≃ 200-400 Å, at z ∼ 2

Abstract : We present physical properties of spectroscopically confirmed Lyα emitters (LAEs) with very large rest-frame Lyα equivalent widths EW0(Lyα). Although the definition of large EW0(Lyα) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from ∼3000 LAEs at z ∼ 2 with reliable measurements of EW0 (Lyα) ≃ 200-400 Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW0(Lyα) LAEs do not have signatures of AGN, but notably small stellar masses of M = 107-8 M and high specific star formation rates (star formation rate per unit galaxy stellar mass) of ∼100 Gyr-1. These LAEs are characterized by the median values of L(Lyα) = 3.7 × 1042 erg s-1 and MUV = -18.0 as well as the blue UV continuum slope of β = -2.5 ± 0.2 and the low dust extinction E(B-V)_* = 0.02^{+0.04}_{-0.02}, which indicate a high median Lyα escape fraction of f_esc^{Lyα }=0.68± 0.30. This large f_esc^{Lyα } value is explained by the low H I column density in the interstellar medium which is consistent with full width at half-maximum (FWHM) of the Lyα line, FWHM(Lyα) = 212 ± 32 km s-1, significantly narrower than those of small EW0(Lyα) LAEs. Based on the stellar evolution models, our observational constraints of the large EW0 (Lyα), the small β, and the rest-frame He II EW imply that at least a half of our large EW0(Lyα) LAEs would have young stellar ages of ≲20 Myr and very low metallicities of Z < 0.02 Z regardless of the star formation history.
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https://hal-insu.archives-ouvertes.fr/insu-03710630
Contributor : Nathalie POTHIER Connect in order to contact the contributor
Submitted on : Friday, July 1, 2022 - 7:40:07 AM
Last modification on : Saturday, September 24, 2022 - 12:02:05 PM

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Takuya Hashimoto, Masami Ouchi, Kazuhiro Shimasaku, Daniel Schaerer, Kimihiko Nakajima, et al.. Lyα emitters with very large Lyα equivalent widths, EW0(Lyα) ≃ 200-400 Å, at z ∼ 2. Monthly Notices of the Royal Astronomical Society, 2017, 465, pp.1543-1562. ⟨10.1093/mnras/stw2834⟩. ⟨insu-03710630⟩

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