Missing dust of super-early galaxies

Context. A subset of very young super-early galaxies at z ≳ 10, often called blue monsters, shows extremely blue UV continua and faint far-IR emission. This might imply much less dust than expected from standard enrichment scenarios. Aims. We wish to understand the reason for the apparent absence of dust in the blue monsters. To do this, we show by combining full 3D hydrodynamical dust-survival yields with 3D thin-shell scalings that clustered supernovae drive a mechanical blowout in stratified self-gravitating clouds, and we predict the retained dust-to-stellar mass ratio at the cluster scale and the corresponding galaxy-integrated value. Methods. We took the net dust yield per unit stellar mass from existing 3D hydrodynamical studies of young stellar clusters with sequential supernovae, and we set the blowout radius as a function of gas concentration using established 3D thin-shell scalings. For an assumed gas–dust coupling across the blowout boundary, the retained dust-to-stellar ratio accounts for the fraction of supernovae that remain confined versus those that vent mechanically. Results. For all typical cluster masses, sizes, and cloud-scale star formation efficiencies, mechanical venting removes a large part of gas and dust. The retained dust-to-stellar mass ratio is lowered by about one-half to two orders of magnitude relative to the supernova net dust yield. The outcome mainly depends on the gas concentration and only weakly on metallicity, and it therefore remains effective at low Z. After weighting by a Schechter cluster mass function and a Weibull core–radius distribution, the galaxy-integrated value falls in the same range inferred for spectroscopically confirmed blue monsters. Conclusions. Mechanical venting at the cluster scale can account for the very low dust fractions inferred for blue monsters without requiring extreme in situ destruction and without fine-tuning.