Dual constraints with ALMA: new [O iii] 88-μm and dust-continuum observations reveal the ISM conditions of luminous LBGs at z ∼ 7. Issue 2 (11th July 2022)

• Record Type: Journal Article
• Authors: Witstok, Joris; Smit, Renske; Maiolino, Roberto; Kumari, Nimisha; Aravena, Manuel; Boogaard, Leindert; Bouwens, Rychard; Carniani, Stefano; Hodge, Jacqueline A; Jones, Gareth C; Stefanon, Mauro; van der Werf, Paul; Schouws, Sander
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 515:Issue 2(2022)
• Page Start: 1751
• Page End: 1773
• Publication Date: 2022-07-11
• Subjects: methods: observational -- techniques: imaging spectroscopy -- galaxies: high-redshift -- dark ages, reionization, first stars -- submillimetre: ISM; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1905
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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 (5 σ ) [${\rm C\, {\small II}}$ ] 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, L IR / L UV, 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.