MMT/MMIRS spectroscopy of z = 1.3-2.4 extreme [O III] emitters: Implications for galaxies in the reionization era

Mengtao Tang, Daniel P. Stark, Jacopo Chevallard, Stéphane Charlot

Research output: Contribution to journalArticle

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Abstract

Galaxies in the reionization era have been shown to have prominent [O III] + Hβ emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at z ≳ 6. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [OIII] emitting galaxies at 1.3 < z<2.4. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses (107-108Mθ) and larger specific star formation rates (5-300 Gyr-1), providing a window on galaxies directly following a burst or recent upturn in star formation. The hydrogen ionizing production efficiency (ξ ion) is found to increase with the [OIII] equivalent width (EW), in a manner similar to that found in local galaxies. We describe how this relationship helps explain the anomalous success rate in identifying Ly α emission in z ≳ 7 galaxies with strong [O III] + Hβ emission. We probe the impact of the intense radiation field on the ISM using O32 and Ne3O2, two ionization-sensitive indices. Both are found to scale with the [OIII] EW, revealing extreme ionization conditions not commonly seen in older and more massive galaxies. In the most intense line emitters, the indices have very large average values (O32 = 9.1, Ne3O2 = 0.5) that have been shown to be linked to ionizing photon escape. We discuss implications for the nature of galaxies most likely to have O32 values associated with significant LyC escape. Finally we consider the optimal strategy for JWST spectroscopic investigations of galaxies at z ≳ 10 where the strongest rest-frame optical lines are no longer visible with NIRSpec.

Original languageEnglish (US)
Pages (from-to)2572-2594
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Volume489
Issue number2
DOIs
StatePublished - Jan 1 2019

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emitters
spectroscopy
galaxies
ionization
radiation distribution
escape
probe
hydrogen
James Webb Space Telescope
ion
star formation rate
stellar mass
gas
complement
light emission
star formation
emerging
bursts
radiation
index

Keywords

  • Cosmology: Observations
  • Galaxies: Evolution
  • Galaxies: Formation
  • Galaxies: High-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

MMT/MMIRS spectroscopy of z = 1.3-2.4 extreme [O III] emitters : Implications for galaxies in the reionization era. / Tang, Mengtao; Stark, Daniel P.; Chevallard, Jacopo; Charlot, Stéphane.

In: Monthly Notices of the Royal Astronomical Society, Vol. 489, No. 2, 01.01.2019, p. 2572-2594.

Research output: Contribution to journalArticle

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abstract = "Galaxies in the reionization era have been shown to have prominent [O III] + Hβ emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at z ≳ 6. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [OIII] emitting galaxies at 1.3 < z<2.4. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses (107-108Mθ) and larger specific star formation rates (5-300 Gyr-1), providing a window on galaxies directly following a burst or recent upturn in star formation. The hydrogen ionizing production efficiency (ξ ion) is found to increase with the [OIII] equivalent width (EW), in a manner similar to that found in local galaxies. We describe how this relationship helps explain the anomalous success rate in identifying Ly α emission in z ≳ 7 galaxies with strong [O III] + Hβ emission. We probe the impact of the intense radiation field on the ISM using O32 and Ne3O2, two ionization-sensitive indices. Both are found to scale with the [OIII] EW, revealing extreme ionization conditions not commonly seen in older and more massive galaxies. In the most intense line emitters, the indices have very large average values (O32 = 9.1, Ne3O2 = 0.5) that have been shown to be linked to ionizing photon escape. We discuss implications for the nature of galaxies most likely to have O32 values associated with significant LyC escape. Finally we consider the optimal strategy for JWST spectroscopic investigations of galaxies at z ≳ 10 where the strongest rest-frame optical lines are no longer visible with NIRSpec.",
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T1 - MMT/MMIRS spectroscopy of z = 1.3-2.4 extreme [O III] emitters

T2 - Implications for galaxies in the reionization era

AU - Tang, Mengtao

AU - Stark, Daniel P.

AU - Chevallard, Jacopo

AU - Charlot, Stéphane

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N2 - Galaxies in the reionization era have been shown to have prominent [O III] + Hβ emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at z ≳ 6. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [OIII] emitting galaxies at 1.3 < z<2.4. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses (107-108Mθ) and larger specific star formation rates (5-300 Gyr-1), providing a window on galaxies directly following a burst or recent upturn in star formation. The hydrogen ionizing production efficiency (ξ ion) is found to increase with the [OIII] equivalent width (EW), in a manner similar to that found in local galaxies. We describe how this relationship helps explain the anomalous success rate in identifying Ly α emission in z ≳ 7 galaxies with strong [O III] + Hβ emission. We probe the impact of the intense radiation field on the ISM using O32 and Ne3O2, two ionization-sensitive indices. Both are found to scale with the [OIII] EW, revealing extreme ionization conditions not commonly seen in older and more massive galaxies. In the most intense line emitters, the indices have very large average values (O32 = 9.1, Ne3O2 = 0.5) that have been shown to be linked to ionizing photon escape. We discuss implications for the nature of galaxies most likely to have O32 values associated with significant LyC escape. Finally we consider the optimal strategy for JWST spectroscopic investigations of galaxies at z ≳ 10 where the strongest rest-frame optical lines are no longer visible with NIRSpec.

AB - Galaxies in the reionization era have been shown to have prominent [O III] + Hβ emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at z ≳ 6. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [OIII] emitting galaxies at 1.3 < z<2.4. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses (107-108Mθ) and larger specific star formation rates (5-300 Gyr-1), providing a window on galaxies directly following a burst or recent upturn in star formation. The hydrogen ionizing production efficiency (ξ ion) is found to increase with the [OIII] equivalent width (EW), in a manner similar to that found in local galaxies. We describe how this relationship helps explain the anomalous success rate in identifying Ly α emission in z ≳ 7 galaxies with strong [O III] + Hβ emission. We probe the impact of the intense radiation field on the ISM using O32 and Ne3O2, two ionization-sensitive indices. Both are found to scale with the [OIII] EW, revealing extreme ionization conditions not commonly seen in older and more massive galaxies. In the most intense line emitters, the indices have very large average values (O32 = 9.1, Ne3O2 = 0.5) that have been shown to be linked to ionizing photon escape. We discuss implications for the nature of galaxies most likely to have O32 values associated with significant LyC escape. Finally we consider the optimal strategy for JWST spectroscopic investigations of galaxies at z ≳ 10 where the strongest rest-frame optical lines are no longer visible with NIRSpec.

KW - Cosmology: Observations

KW - Galaxies: Evolution

KW - Galaxies: Formation

KW - Galaxies: High-redshift

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