Dust attenuation evolution in $z \sim 2$-$12$ JWST galaxies

TL;DR

This study analyzes dust attenuation in galaxies from redshift 2 to 12 using JWST data, revealing the evolution of dust properties and the first detection of the UV bump at z ~ 7.55, shedding light on dust formation in the early universe.

Contribution

It provides the first detection of the UV bump at high redshift and demonstrates how dust attenuation features evolve over cosmic time, highlighting early dust formation mechanisms.

Findings

Detection of UV bump at z ~ 7.55 in a galaxy.

Decrease in power-law slope and bump strength with increasing redshift.

Early universe dust likely formed in supernova ejecta with minimal processing.

Abstract

A sizable fraction of the heavy elements synthesized by stars in galaxies condenses into sub-micron-sized solid-state particles, known as dust grains. Dust produces a wavelength-dependent attenuation, $A_\lambda$, of the galaxy emission, thereby significantly altering its observed properties. Locally, $A_\lambda$ is in general the sum of a power-law and a UV feature ('bump') produced by small, carbon-based grains. However, scant information exists regarding its evolution across cosmic time. Here, leveraging data from 173 galaxies observed by the James Webb Space Telescope in the redshift range z = 2 - 12, we report the most distant detection of the UV bump in a z ~ 7.55 galaxy (when the Universe was only ~ 700 Myr old), and show for the first time that the power-law slope and the bump strength decrease towards high redshifts. We propose that the flat $A_\lambda$ shape at early epochs is produced by large grains newly formed in supernova ejecta, which act as the main dust factories at such early epochs. Importantly, these grains have undergone minimal reprocessing in the interstellar medium due to the limited available cosmic time. This discovery opens new perspectives in the study of cosmic dust origin and evolution.