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Witstok, J, Smit, R, Maiolino, R, Curti, M, Laporte, N, Massey, R, Richard, J and Swinbank, M (2021) Assessing the sources of reionization: a spectroscopic case study of a 30 x lensed galaxy at z similar to 5 with Ly alpha, C IV, Mg II, and [Ne III]. Monthly Notices of the Royal Astronomical Society, 508 (2). pp. 1686-1700. ISSN 0035-8711
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Abstract
We present a detailed spectroscopic analysis of a galaxy at z ≃ 4.88 that is, by chance, magnified ∼30× by gravitational lensing. Only three sources at z ≳ 5 are known with such high magnification. This particular source has been shown to exhibit widespread, high equivalent width CIV λ1549A˚ emission, implying it is a unique example of a metal-poor galaxy with a hard radiation field, likely representing the galaxy population responsible for cosmic reionization. Using ultraviolet (UV) nebular line ratio diagnostics, Very Large Telescope (VLT)/X-shooter observations rule out strong active galactic nuclei (AGN) activity, indicating a stellar origin of the hard radiation field instead. We present a new detection of [NeIII] λ3870A˚ and use the [NeIII]/[OII] line ratio to constrain the ionization parameter and gas-phase metallicity. Closely related to the commonly used [OIII]/[OII] ratio, our [NeIII]/[OII] measurement shows this source is similar to local ‘Green Pea’ galaxies and Lyman-continuum leakers. It furthermore suggests this galaxy is more metal poor than expected from the fundamental metallicity relation, possibly as a consequence of excess gas accretion diluting the metallicity. Finally, we present the highest redshift detection of MgII λ2796A˚, observed at high equivalent width in emission, in contrast to more evolved systems predominantly exhibiting MgII absorption. Strong MgII emission has been observed in most z ∼ 0 Lyman-continuum leakers known and has recently been proposed as an indirect tracer of escaping ionizing radiation. In conclusion, this strongly lensed galaxy, observed just 300Myr after reionization ends, enables testing of observational diagnostics proposed to constrain the physical properties of distant galaxies in the James Webb Space Telescope (JWST)/Extremely Large Telescope (ELT) era.
| Item Type: | Article |
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| Additional Information: | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| Uncontrolled Keywords: | Astronomy & Astrophysics; CENT LEAKAGE; dark ages, reionization, first stars; EMISSION-LINE DIAGNOSTICS; FIELD; FUNDAMENTAL RELATION; galaxies: high-redshift; GAS; gravitational lensing: strong; MASS-METALLICITY RELATION; methods: observational; NEBULAR EMISSION; Physical Sciences; Science & Technology; STAR-FORMING GALAXIES; STELLAR MASS; techniques: spectroscopic; ULTRAVIOLET-SPECTRA; Science & Technology; Physical Sciences; Astronomy & Astrophysics; gravitational lensing: strong; methods: observational; techniques: spectroscopic; galaxies: high-redshift; dark ages, reionization, first stars; STAR-FORMING GALAXIES; MASS-METALLICITY RELATION; EMISSION-LINE DIAGNOSTICS; STELLAR MASS; FUNDAMENTAL RELATION; NEBULAR EMISSION; ULTRAVIOLET-SPECTRA; CENT LEAKAGE; GAS; FIELD; Science & Technology; Physical Sciences; Astronomy & Astrophysics; gravitational lensing: strong; methods: observational; techniques: spectroscopic; galaxies: high-redshift; dark ages, reionization, first stars; MASS-METALLICITY RELATION; STAR-FORMING GALAXIES; EMISSION-LINE DIAGNOSTICS; STELLAR MASS; FUNDAMENTAL RELATION; NEBULAR EMISSION; MOSDEF SURVEY; X-SHOOTER; ULTRAVIOLET-SPECTRA; CENT LEAKAGE; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics |
| Subjects: | Q Science > QB Astronomy |
| Divisions: | Astrophysics Research Institute |
| Publisher: | Oxford University Press |
| SWORD Depositor: | A Symplectic |
| Date Deposited: | 10 Oct 2022 14:49 |
| Last Modified: | 10 Oct 2022 15:12 |
| DOI or ID number: | 10.1093/mnras/stab2591 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/17790 |
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