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

TL;DR

This study uses extensive ALMA and NOEMA observations to search for dust in galaxies beyond redshift 8, finding no significant dust emission and constraining dust properties, which suggests inefficient dust formation in the early universe.

Contribution

The paper provides the first deep, multi-band millimeter observations of ten galaxies at z > 8, setting stringent limits on dust mass and dust-to-stellar mass ratios in the early universe.

Findings

No significant dust emission detected in z > 8 galaxies.

Dust masses are constrained to be below 10^5 M_sun at 3 sigma.

Results support inefficient dust build-up due to limited production and grain growth.

Abstract

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 $T_{\rm dust} = 50$ K and $\beta_{\rm dust} = 2.0$). Binning by redshift ($8 < z < 9.5$ and $9.5 < z < 15$), UV-continuum slope ($\beta_{\rm UV} \lessgtr -2$) and stellar mass ($\log_{10} M_{\ast}/{\rm M_{\odot}} \lessgtr 9$) 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.