We present new [${\rm O\, {\small III}}$] 88-$\mu \mathrm{{m}}$ observations of five bright z ∼ 7 Lyman-break galaxies spectroscopically confirmed by ALMA through [${\rm C\, {\small II}}$] 158 $\mu \mathrm{{m}}$, unlike recent [${\rm O\, {\small III}}$] detections where Lyman α was used. This nearly doubles the sample of Epoch of Reionization galaxies with robust (5σ) [${\rm C\, {\small II}}$] and [${\rm O\, {\small III}}$] detections. We perform a multiwavelength comparison with new deep HST images of the rest-frame UV, whose compact morphology aligns well with [${\rm O\, {\small III}}$] tracing ionized gas. In contrast, we find more spatially extended [${\rm C\, {\small II}}$] emission likely produced in neutral gas, as indicated by an [${\rm N\, {\small II}}$] 205-$\mu \mathrm{{m}}$ non-detection in one source. We find a correlation between the optical ${[{\rm O\, {\small III}}]}+ {\mathrm{H\,\beta }}$ equivalent width and [${\rm O\, {\small III}}$]/[${\rm C\, {\small II}}$], as seen in local metal-poor dwarf galaxies. cloudy models of a nebula of typical density harbouring a young stellar population with a high-ionization parameter adequately reproduce the observed lines. Surprisingly, however, our models fail to reproduce the strength of [${\rm O\, {\small III}}$] 88-$\mu \mathrm{{m}}$, unless we assume an α/Fe enhancement and near-solar nebular oxygen abundance. On spatially resolved scales, we find [${\rm O\, {\small III}}$]/[${\rm C\, {\small II}}$] shows a tentative anticorrelation with infrared excess, LIR/LUV, also seen on global scales in the local Universe. Finally, we introduce the far-infrared spectral energy distribution fitting code mercurius to show that dust-continuum measurements of one source appear to favour a low dust temperature and correspondingly high dust mass. This implies a high stellar metallicity yield and may point towards the need of dust production or grain-growth mechanisms beyond supernovae.
We present the first detection of the [N ii] 122 $\mu$m and [O iii] 52 $\mu$m lines for a reionization-epoch galaxy. Based on these lines and previous [C ii] 158 $\mu$m and [O iii] 88 $\mu$m measurements, using two different radiative transfer models of the interstellar medium, we estimate an upper limit on electron density of ≲500 cm−3 and an approximate gas-phase metallicity of Z/Z⊙ ∼ 1.1 ± 0.2 for A1689-zD1, a gravitationally lensed dusty galaxy at z = 7.133. Other measurements or indicators of metallicity so far in galaxy interstellar media at z ≳ 6 are typically an order of magnitude lower than this. The unusually high metallicity makes A1689-zD1 inconsistent with the fundamental metallicity relation, although there is likely significant dust obscuration of the stellar mass, which may partly resolve the inconsistency. Given a solar metallicity, the dust-to-metals ratio is a factor of several lower than expected, hinting that galaxies beyond z ∼ 7 may have lower dust formation efficiency. Finally, the inferred nitrogen enrichment compared to oxygen, on which the metallicity measurement depends, indicates that star formation in the system is older than about 250 Myr, pushing the beginnings of this galaxy to z > 10.
more » « less- NSF-PAR ID:
- 10402112
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 521
- Issue:
- 2
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 2526-2534
- Size(s):
- ["p. 2526-2534"]
- Sponsoring Org:
- National Science Foundation
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