Probing Infrared eXcess to Investigate Early-Universe Dust (PIXIEDust)

Despite the implied presence of dust through reddened UV emission in high-redshift galaxies, no dust emission has been detected in the (sub)millimetre regime beyond $z>8.3$. This study combines around two hundred hours of Atacama Large Millimeter/submillimeter Array (ALMA) and Northern Extended Millimeter Array (NOEMA) observations on ten $z>8$ galaxies, revealing no significant dust emission down to a $1\sigma$ depth of $2.0$, $2.0$, and $1.5\mu$Jy at rest-frame 158, 88 $\mu$m, and across all the data, respectively. This constrains average dust masses to be below $<{10}^5$ M${}_{\odot }$ at $3\sigma$ and dust-to-stellar mass ratios to be below $3.7\times {10}^{-4}$ (assuming $T_{\mathrm{d}\mathrm{u}\mathrm{s}\mathrm{t}}=50$ K and ${\beta }_{\mathrm{d}\mathrm{u}\mathrm{s}\mathrm{t}}=2.0$). Binning by redshift ($8<z<9.5$ and $9.5<z<15$), UV-continuum slope (${\beta }_{\mathrm{U}\mathrm{V}}\lessgtr -2$) and stellar mass (${\log }_{10}{M}_{\ast }\mathrm{/}{\mathrm{M}}_{\odot }\lessgtr 9$) yields similarly stringent constraints. Combined with other studies, these results are consistent with inefficient dust build-up in the $z>8$ Universe, likely due to inefficient supernova production, limited interstellar grain growth and/or ejection by outflows. We provide data and tools online to facilitate community-wide high-redshift dust searches.