Ly$α$ Emitters with Very Large Ly$α$ Equivalent Widths, EW$_{\rm 0}$(Ly$α$) $\simeq 200-400$ Å, at $z\sim 2$

Takuya Hashimoto; Masami Ouchi; Kazuhiro Shimasaku; Daniel Schaerer; Kimihiko Nakajima; Takatoshi Shibuya; Yoshiaki Ono; Michael Rauch; Ryosuke Goto

doi:10.1093/mnras/stw2834

paper

Ly $α$ Emitters with Very Large Ly $α$ Equivalent Widths, EW $_{0}$ (Ly $α$ ) $≃ 200 - 400$ Å, at $z \sim 2$

arXiv:1611.00777 · doi:10.1093/mnras/stw2834

Abstract

We present physical properties of spectroscopically confirmed Ly $α$ emitters (LAEs) with very large rest-frame Ly $α$ equivalent widths EW $_{0}$ (Ly $α$ ). Although the definition of large EW $_{0}$ (Ly $α$ ) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from $\sim 3000$ LAEs at $z \sim 2$ with reliable measurements of EW $_{0}$ (Ly $α$ ) $≃ 200 - 400$ Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW $_{0}$ (Ly $α$ ) LAEs do not have signatures of AGN, but notably small stellar masses of $M_{*} = 1 0^{7 - 8}$ $M_{⊙}$ and high specific star-formation rates (star formation rate per unit galaxy stellar mass) of $\sim 100$ Gyr $^{- 1}$ . These LAEs are characterized by the median values of $L (Ly α) = 3.7 \times 1 0^{42}$ erg s $^{- 1}$ and $M_{UV} = - 18.0$ as well as the blue UV continuum slope of $β = - 2.5 \pm 0.2$ and the low dust extinction $E (B - V)_{*} = 0.0 2_{- 0.02}^{+ 0.04}$ , which indicate a high median Ly $α$ escape fraction of $f_{esc}^{Ly α} = 0.68 \pm 0.30$ . This large $f_{esc}^{Ly α}$ value is explained by the low {\sc Hi} column density in the ISM that is consistent with FWHM of the Ly $α$ line, $FWHM (Ly α) = 212 \pm 32$ km s $^{- 1}$ , significantly narrower than those of small EW $_{0}$ (Ly $α$ ) LAEs. Based on the stellar evolution models, our observational constraints of the large EW $_{0}$ (Ly $α$ ), the small $β$ , and the rest-frame He{\sc ii} equivalent width imply that at least a half of our large EW $_{0}$ (Ly $α$ ) LAEs would have young stellar ages of $≲ 20$ Myr and very low metallicities of $Z < 0.02 Z_{⊙}$ regardless of the star-formation history.

arXiv commentAccepted for publication in MNRAS; 23 pages with 16 figures

Ly $α$ Emitters with Very Large Ly $α$ Equivalent Widths, EW $_{0}$ (Ly $α$ ) $≃ 200 - 400$ Å, at $z \sim 2$

Abstract

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Lyα Emitters with Very Large Lyα Equivalent Widths, EW0​(Lyα) ≃200−400 Å, at z∼2

Abstract

References in corpus (108)

Cited by in corpus (22)

Ly $α$ Emitters with Very Large Ly $α$ Equivalent Widths, EW $_{0}$ (Ly $α$ ) $≃ 200 - 400$ Å, at $z \sim 2$