CEERS: Forging the First Dust Grains in the Universe? A Population of Galaxies with spectroscopically-derived Extremely Low Dust Attenuation (GELDA) at 4.0<z<11.4

Abstract

We investigate the coevolution of metals and dust in 173 galaxies at $4.0<z<11.4$ using NIRSpec spectroscopy. Focusing on galaxies with extremely low dust attenuation, we explore their physical processes using a new CIGALE version that incorporates spectroscopic and photometric data. Comparing observations with models, we derive key physical parameters. We identify 49 galaxies with extremely low dust attenuation (GELDAs), characterized by $A_{FUV}=0$ within $2\ddot{I}ƒ$ and $M_{star}<10^9{M}_{\odot }$. The stacked spectra reveal a very blue UV slope (${\hat{I}}_{FUV}^2=-2.451\pm -0.066$) and Balmer decrement H$\hat{I}\pm$/H${\hat{I}}^2=2.932\pm -0.660$, consistent with no dust attenuation. GELDAs are more common at $z>8.8$ (83.3%) than at $z<8.8$ (26.3%) suggesting they dominate the early Universe. Assuming a prior FIR dust spectrum (from ALPINE), we examine dust-stellar mass trends. The $M_{dust}$ vs. $M_{star}$ diagram shows upper and lower sequences linked by possible transitional galaxies. A transition at $M_{star}=10^8.5M_{\odot }$ ($Z_{crit}=12+{\log }_{10}(O/H)=7.60$ or $Z/Z_{\odot }=0.1$) may mark the shift from stellar dust production to ISM grain growth, in agreement with theoretical predictions. Our full sample has a high mean gas fraction ($f_{gas}>0.9$), indicating retained gas across all galaxies. Their small sizes and large gas masses imply high gas surface densities but relatively low star formation efficiency. High-redshift GELDAs may naturally explain the observed excess of bright galaxies at $z>9$ compared to theoretical expectations.

Accepted in A&A (May 2025)