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Title: AVERAGE METALLICITY AND STAR FORMATION RATE OF Ly{alpha} EMITTERS PROBED BY A TRIPLE NARROWBAND SURVEY

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}, [O II]{lambda}3727, and H{alpha}+[N II] 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 [O II] and 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 H{alpha} luminosity of 1.7 Multiplication-Sign 10{sup 42} erg s{sup -1} corresponding to an SFR of 14 M{sub Sun} yr{sup -1}. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z {approx}> 0.09 Z{sub Sun} (2{sigma}) based on the [O II]/(H{alpha}+[N II]) index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z {approx} 2, are extremely metal-poor (Z <more » 2 Multiplication-Sign 10{sup -2} Z{sub Sun }) galaxies at the 4{sigma} level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z {approx} 2 UV-selected galaxies toward lower masses (5 Multiplication-Sign 10{sup 8} M{sub Sun }), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The H{alpha} and Ly{alpha} luminosities of our NB-selected LAEs indicate that the escape fraction of Ly{alpha} photons is {approx}12%-30%, much higher than the values derived for other galaxy populations at z {approx} 2.« less

Authors:
; ; ;  [1];  [2]; ;  [3];  [4];  [5];  [6];  [7];  [8]
  1. Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
  2. Institute for the Physics and Mathematics of the Universe (IPMU), TODIAS, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)
  3. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  4. Department of Earth Sciences, National Taiwan Normal University, No. 88, Tingzhou Road, Sec. 4, Taipei 11677, Taiwan (China)
  5. Department of Physics and Astronomy, University of Wyoming, Laramie, WY (United States)
  6. Department of Astronomy, Indiana University, Bloomington, IN (United States)
  7. Department of Physics, Siena College, Loudonville, NY (United States)
  8. School of Physics and Astronomy, University of Nottingham, Nottingham (United Kingdom)
Publication Date:
OSTI Identifier:
22012016
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 745; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; GALACTIC EVOLUTION; GALAXIES; LUMINOSITY; PHOTOIONIZATION; RED SHIFT; SPECTROSCOPY; STARS

Citation Formats

Nakajima, Kimihiko, Shimasaku, Kazuhiro, Ono, Yoshiaki, Okamura, Sadanori, Ouchi, Masami, Lee, Janice C, Ly, Chun, Foucaud, Sebastien, Dale, Daniel A, Salim, Samir, Finn, Rose, and Almaini, Omar. AVERAGE METALLICITY AND STAR FORMATION RATE OF Ly{alpha} EMITTERS PROBED BY A TRIPLE NARROWBAND SURVEY. United States: N. p., 2012. Web. doi:10.1088/0004-637X/745/1/12.
Nakajima, Kimihiko, Shimasaku, Kazuhiro, Ono, Yoshiaki, Okamura, Sadanori, Ouchi, Masami, Lee, Janice C, Ly, Chun, Foucaud, Sebastien, Dale, Daniel A, Salim, Samir, Finn, Rose, & Almaini, Omar. AVERAGE METALLICITY AND STAR FORMATION RATE OF Ly{alpha} EMITTERS PROBED BY A TRIPLE NARROWBAND SURVEY. United States. https://doi.org/10.1088/0004-637X/745/1/12
Nakajima, Kimihiko, Shimasaku, Kazuhiro, Ono, Yoshiaki, Okamura, Sadanori, Ouchi, Masami, Lee, Janice C, Ly, Chun, Foucaud, Sebastien, Dale, Daniel A, Salim, Samir, Finn, Rose, and Almaini, Omar. 2012. "AVERAGE METALLICITY AND STAR FORMATION RATE OF Ly{alpha} EMITTERS PROBED BY A TRIPLE NARROWBAND SURVEY". United States. https://doi.org/10.1088/0004-637X/745/1/12.
@article{osti_22012016,
title = {AVERAGE METALLICITY AND STAR FORMATION RATE OF Ly{alpha} EMITTERS PROBED BY A TRIPLE NARROWBAND SURVEY},
author = {Nakajima, Kimihiko and Shimasaku, Kazuhiro and Ono, Yoshiaki and Okamura, Sadanori and Ouchi, Masami and Lee, Janice C and Ly, Chun and Foucaud, Sebastien and Dale, Daniel A and Salim, Samir and Finn, Rose and Almaini, Omar},
abstractNote = {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}, [O II]{lambda}3727, and H{alpha}+[N II] 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 [O II] and 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 H{alpha} luminosity of 1.7 Multiplication-Sign 10{sup 42} erg s{sup -1} corresponding to an SFR of 14 M{sub Sun} yr{sup -1}. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z {approx}> 0.09 Z{sub Sun} (2{sigma}) based on the [O II]/(H{alpha}+[N II]) index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z {approx} 2, are extremely metal-poor (Z < 2 Multiplication-Sign 10{sup -2} Z{sub Sun }) galaxies at the 4{sigma} level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z {approx} 2 UV-selected galaxies toward lower masses (5 Multiplication-Sign 10{sup 8} M{sub Sun }), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The H{alpha} and Ly{alpha} luminosities of our NB-selected LAEs indicate that the escape fraction of Ly{alpha} photons is {approx}12%-30%, much higher than the values derived for other galaxy populations at z {approx} 2.},
doi = {10.1088/0004-637X/745/1/12},
url = {https://www.osti.gov/biblio/22012016}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 745,
place = {United States},
year = {Fri Jan 20 00:00:00 EST 2012},
month = {Fri Jan 20 00:00:00 EST 2012}
}