We report on the detection of the [C ii] 157.7 µm emission from the Lyman break galaxy (LBG) MACS0416 Y1 at z = 8.3113, by using the Atacama Large Millimeter/submillimeter Array (ALMA). The luminosity ratio of [O iii] 88 µm (from previous campaigns) to [C ii] is 9.3 ± 2.6, indicative of hard interstellar radiation fields and/or a low covering fraction of photo-dissociation regions. The emission of [C ii] is cospatial to the 850 µm dust emission (90 µm rest-frame, from previous campaigns), however the peak [C ii] emission does not agree with the peak [O iii] emission, suggesting that the lines originate from different conditions in the interstellar medium. We fail to detect continuum emission at 1.5 mm (160 µm rest-frame) down to 18 µJy (3σ). This non-detection places a strong limits on the dust-spectrum, considering the 137 ± 26 µJy continuum emission at 850 µm. This suggests an unusually warm dust component (T > 80 K, 90% confidence limit), and/or a steep dust-emissivity index (βdust > 2), compared to galaxy-wide dust emission found at lower redshifts (typically T ∼ 30 − 50 K, βdust ∼ 1 − 2). If such temperatures are common, this would reduce the required dust mass and relax the dust production problem at the highest redshifts. We therefore warn against the use of only single-wavelength information to derive physical properties, recommend a more thorough examination of dust temperatures in the early Universe, and stress the need for instrumentation that probes the peak of warm dust in the Epoch of Reionization.
|Publication status||Published - 2020 Jan 8|
- Galaxies: formation
- Galaxies: high-redshift
- Galaxies: ISM
ASJC Scopus subject areas