Kavli Affiliate: Roberto Maiolino
| First 5 Authors: , , , ,
| Summary:
Dust is a fundamental component of the interstellar medium within galaxies,
as dust grains are highly efficient absorbers of ultraviolet (UV) and optical
photons. Accurately quantifying this obscuration is crucial for interpreting
galaxy spectral energy distributions (SEDs). The extinction curves in the Milky
Way (MW) and Large Magellanic Cloud exhibit a strong feature known as the 2175
AA UV bump, most often attributed to small carbonaceous dust grains. This
feature was recently detected in faint galaxies out to z=7.55, suggesting rapid
formation channels. Here, we report the detection of a strong UV bump in a
luminous Lyman-break galaxy at z_prism=7.11235, GNWY-7379420231, through
observations taken as part of the NIRSpec Wide GTO survey. We fit a dust
attenuation curve that is consistent with the MW extinction curve within
1sigma, in a galaxy just ~700 Myr after the Big Bang. From the integrated
spectrum, we infer a young mass-weighted age (t~22-59 Myr) for this galaxy,
however spatially resolved SED fitting unveils the presence of an older stellar
population (t~252 Myr). Furthermore, morphological analysis provides evidence
for a potential merger. The underlying older stellar population suggests the
merging system could be pre-enriched, with the dust illuminated by a
merger-induced starburst. Moreover, turbulence driven by stellar feedback in
this bursty region may be driving polycyclic aromatic hydrocarbon formation
through top-down shattering. The presence of a UV bump in GNWY-7379420231
solidifies growing evidence for the rapid evolution of dust properties within
the first billion years of cosmic time
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