Show simple item record Nakajima, K. en Ouchi, M. en Shimasaku, K. en Ono, Y. en Lee, J.C. en Foucad, S. en Ly, C. en Dale, D.A. en Salim, S. en Finn, R. en Almaini, O. en Okamura, S. en 2014-10-30T20:13:38Z en 2014-10-30T20:13:38Z en 2012 en
dc.identifier.citation Nakajima, K., Ouchi, M., Shimasaku, K., Ono, Y., Lee, J. C., Foucaud, S., . . . Okamura, S. (2012). Average metallicity and star formation rate of Ly$\alpha$ emitters probed by a triple narrowband survey. Astrophysical Journal, 745(1), 12. en
dc.description *Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. en
dc.description.abstract We present the average metallicity and star formation rate (SFR) of $Ly\alpha$ emitters (LAEs) measured from our large-area survey with three narrowband (NB) filters covering the $Ly\alpha, \big[O II\big]\lambda3727$, and $\text{H}\alpha+\big[\text{N} II\big]$ lines of LAEs at $z = 2.2$. We select 919 $z = 2.2$ LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted $\big[\text{O} II\big]$ and $\text{H}\alpha$ nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by NB imaging or deep spectroscopy. The stacked object has an Hα luminosity of $1.7 × 10^{42} erg s^{–1}$ corresponding to an SFR of $14 M_{\odot} yr6{–1}$. We place, for the first time, a firm lower limit to the average metallicity of LAEs of $Z \gtrsim 0.09 Z_{\odot} \big(2\sigma\big)$ based on the $\big[\text{O} II\big]/\big(\text{H}\alpha+\big[\text{N} II\big]\big)$ index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at $z \sim 2$, are extremely metal-poor $\big(Z < 2 × 10–2 Z_{\odot}\big)$ galaxies at the $4\sigma$ level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of $z \sim 2$ UV-selected galaxies toward lower masses $\big(5 × 108 M_{\odot}\big)$, but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The $\text{H}\alpha$ and $\text{Ly}\alpha$ luminosities of our NB-selected LAEs indicate that the escape fraction of $\text{Ly}\alpha$ photons is $\sim12%-30%$, much higher than the values derived for other galaxy populations at $z \sim 2$. en
dc.language.iso en_US en
dc.publisher The American Astronomical Society en
dc.relation.isversionof en
dc.rights © 2012 The American Astronomical Society en
dc.subject galaxies: abundances en
dc.subject galaxies: evolution en
dc.subject galaxies: formation en
dc.subject galaxies: high-redshift en
dc.subject galaxies: star formation en
dc.title Average metallicity and star formation rate of Ly$\alpha$ emitters probed by a triple narrowband survey* en
dc.type Article en
dc.altmetrics.display true en

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