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Recent attempts to detect [O  iii ] 88 |$\, \mu$| m emission from super-early (z > 10) galaxy candidates observed by JWST have been unsuccessful. Non-detections can be either due to wrong photometric redshifts or to the faintness of the line in such early systems. By using zoom-in simulations, we show that if redshifts of these galaxies are confirmed, they are faint and mostly fall below the local metal-poor |$\rm [O\, {\small III}]-SFR$| relation as a result of their low ionization parameter, U ion ≲ 10−3. Such low U ion values are found in galaxies that are in an early assembly stage, and whose stars are still embedded in high-density natal clouds. However, the most luminous galaxy in our sample (⁠|$\rm {log}[L_{\rm {[O\, {\small III}]}}/\mathrm{L}_\odot ] = 8.4$|⁠ , U ion ≈ 0.1) could be detected by ALMA in only 2.8 h. [ABSTRACT FROM AUTHOR]

We report new deep observations obtained with the Atacama Large Millimetre Array (ALMA) aimed at investigating the [C II]158 μm line and continuum emission in three spectroscopically confirmed Lyman break galaxies at 6.8 < z ≤ 7.1, i.e. well within the re-ionization epoch. With star formation rates of SFR ∼ 5-15M⊙ yr-1 these systems are much more representative of the high-z galaxy population than other systems targeted in the past by millimetre observations. For the galaxy with the deepest observation we detect [C II] emission at redshift z = 7.107, fully consistent with the Ly α redshift, but spatially offset by 0.7 arcsec (4 kpc) from the optical emission. At the location of the optical emission, tracing both the Ly α line and the far-UV continuum, no [C II] emission is detected in any of the three galaxies, with 3σ upper limits significantly lower than the [C II] emission observed in lower redshift galaxies. These results suggest that molecular clouds in the central parts of primordial galaxies are rapidly disrupted by stellar feedback. As a result, [C II] emission mostly arises from more external accreting/satellite clumps of neutral gas. These findings are in agreement with recent models of galaxy formation. Thermal far-infrared continuum is not detected in any of the three galaxies. However, the upper limits on the infrared-to-UV emission ratio do not exceed those derived in metal- and dust-poor galaxies. [ABSTRACT FROM AUTHOR]