On the missing dust of super-early galaxies: Supernova blowout and gas-dust venting in Blue Monsters

TL;DR

Blue Monsters at $z\gtrsim10$ exhibit exceptionally blue UV slopes and faint far-IR emission, implying unusually low dust content. The authors couple full 3-D hydrodynamical simulations of dust production and survival in young star clusters with sequential supernovae to thin-shell blowout scalings, predicting the retained dust-to-stellar mass ratio $\xi_d$ at both cluster and galaxy scales. They find mechanical venting reduces $\xi_d$ by about $0.5$ to $2$ dex relative to the net SN dust yield, with the galaxy-averaged value $\langle\xi_d\rangle_{gal}$ typically near $\log\langle\xi_d\rangle_{gal} \approx -4$, and this result is robust to metallicity changes. After CMF and core-radius weighting, the predicted $\log\langle\xi_d\rangle_{gal}$ aligns with dust fractions inferred for spectroscopically confirmed Blue Monsters, offering a natural explanation for their transparency without invoking extreme in situ destruction or fine tuning, and predicting that most early galaxies should be permeable along blowout channels while a minority of very massive, compact clusters can retain more dust.

Abstract

A subset of very young, super-early galaxies at $z\gtrsim10$, often termed Blue Monsters, shows extremely blue UV continua and faint far-IR emission, which could imply much less dust than expected from standard enrichment scenarios. We seek to understand the possible reason behind the apparent absence of dust in the Blue Monsters. We show how clustered supernovae drive mechanical blowout in stratified, self-gravitating clouds by combining full 3-D hydrodynamical dust-survival yields with 3-D thin-shell scalings, and we predict the retained dust-to-stellar mass ratio at the cluster scale and the corresponding galaxy-integrated value. We take the net dust yield per unit stellar mass from existing 3-D hydrodynamical studies of young stellar clusters with sequential supernovae, and we set the blowout radius as a function of gas concentration using established 3-D thin-shell scalings. Assuming 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. Across typical cluster masses, sizes, and cloud-scale star formation efficiencies, mechanical venting removes a large share of gas and dust. The retained dust-to-stellar mass ratio is lowered by about half to two orders of magnitude relative to the supernova net dust yield. The outcome depends mainly on gas concentration and only weakly on metallicity, so it 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. Thus, 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.

Figures (2)

• Figure 1: Predicted retained dust-to-stellar mass ratio for star clusters as a function of stellar mass and star cluster core radius, shown for cloud-scale star formation efficiencies $\varepsilon_\star=0.10$ (upper panel), $0.50$ (lower panel). Colors encode $\log\xi_{d}=\log\![\xi_{d,0}\,(1-f_{\rm mech})]$ with $\xi_{d,0}=2.14\times10^{-3}$. The dashed black curves mark $f_{\rm mech}=0.5$, and the solid black contours display $\log\xi_{d}=-4$, the characteristic level inferred for Blue Monsters.
• Figure 2: Galaxy-integrated dust-to-stellar mass ratio versus the cloud-scale star-formation efficiency. The solid blue curve corresponds to $\log\xi_{d,0} \simeq -2.669$, while the dashed blue curve corresponds to a factor-of-two reduction in $\xi_{d,0}$, consistent with either reduced supernova dust mass production or reduced dust survival. The horizontal solid line marks $\log\langle\xi_d\rangle_{\rm gal}=-4$. Dotted horizontal lines annotate $\log\langle\xi_d\rangle_{\rm gal}$ for a subset of spectroscopically-confirmed Blue Monsters as inferred by Ferraraetal2025.