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.
B[e] supergiants (sgB[e]) are rare objects whose evolutionary stage remains uncertain. Observationally, they display strong Balmer emission lines, infrared excess, and intrinsic polarization, indicating a non-spherical circumstellar envelope. We present a study of the sgB[e] RMC 82, using new spectropolarimetric data complemented by photometry from the ultraviolet (UV) to the mid-infrared. Our two-component model comprises a slow, dense equatorial wind wherein dust grains form and a fast polar wind. We applied the hdust radiative transfer code and Bayesian statistics to infer the parameters from a grid of 3240 pre-computed models. The model accurately reproduces the spectral energy distribution and polarized spectrum, but struggles to match the H α emission. Our results suggest a large mass-loss rate of $6.6 \times 10^{-6}\, \mathrm{{\rm M}_{\odot }\, yr^{-1}\, sr^{-1}}$. The dense wind is confined within an opening angle of 11°. The hottest dust grains are located at 277 R* with a temperature of 870 K. The dust grains are porous, with a density of 0.051 $\rm {g\, cm^{-3}}$. The central star was found to be significantly hotter than previous estimates (Teff = $27\, 000$ K). By comparing models with different components, we find that gas reprocesses a significant amount of UV radiation, shielding the dust. However, the dust also scatters UV photons back to the inner disc, increasing its temperature and H α emission. We conclude that self-consistent models, that account for the gas–dust interplay in the envelope, are essential for studying sgB[e] and similar objects.
more » « less- NSF-PAR ID:
- 10485722
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 528
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 122-140
- Size(s):
- ["p. 122-140"]
- Sponsoring Org:
- National Science Foundation
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