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Italy Large dust reservoirs (up to approximately 108M&Odot;) have been detected13 in galaxies out to redshift z ≃ 8, when the age of the Universe was only about 600 Myr. Generating substantial amounts of dust within such a short timescale has proven challenging for theories of dust formation4,5 and has prompted the revision ofthe modelling of potential sites of dust production6-8, such asthe atmospheres of asymptotic giant branch stars in low-metallicity environments, supernova ejecta and the accelerated growth ofgrains in the interstellar medium. However, degeneracies between different evolutionary pathways remain when the total dust mass of galaxies is the only available observable. Here we report observations of the 2,175 Å dust attenuation feature, which is well known in the Milky Way and galaxies at z ≃ 3 (refs. 9-11), in the near-infrared spectra of galaxies up to z ≃ 7, correspondingto the first billion years of cosmic time. The relatively short timescale implied forthe formation of carbonaceous grainsgiving rise to this feature12 suggests a rapid production process, possibly in Wolf-Rayet stars or supernova
As part of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey ( JADES), we obtained deep Near-Infrared Spectrograph (NIRSpec) multi-object spectroscopic data taken in the PRISM configuration (spectral range 0.6 to 5.3 µm and resolving power R ≃ 100). Using the NIRSpec micro-shutter array (MSA), we observed 253 sources across three visits between 21 and 25 October 2022 ( JWST programme 1210; principal investigator (PI): Lützgendorf), with exposure times per object ranging from 9.3 to 28 h. The extracted one-dimensional spectra reached a continuum sensitivity (3σ) of approximately 6-40 × 10-22 erg s-1 cm-2 Å-1 (27.2-29.1 AB magnitude) at approximately 2 µm. Targets were selected with a specific focus on high-redshiftgalaxies in imaging taken with the Hubble Space Telescope and JWST/Near-Infrared Camera (NIRCam).
Through a visual inspection of all spectra, we found strong evidence of an absorption feature around a rest-frame wavelength λemit = 2,175 Å in the spectrum of a galaxy at z = 6.71 ( JADES-GS+53.15138-27.81917; JADES-GS-z6-0 hereafter), which was revealed via a significant (6σ) deviation from a smooth power-law continuum, as shown in Fig. 1. This feature, known as the ultraviolet (UV) attenuation 'bump', was first discovered by Stecher (1965) along sightlines in the...