Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Tobias J. Looser, Francesco D’Eugenio, Roberto Maiolino, Joris Witstok, Lester Sandles
| Summary:
Local and low-redshift ($z$<$3$) galaxies are known to broadly follow a
bimodal distribution: actively star forming galaxies with relatively stable
star-formation rates, and passive systems. These two populations are connected
by galaxies in relatively slow transition. In contrast, theory predicts that
star formation was stochastic at early cosmic times and in low-mass systems:
these galaxies transitioned rapidly between starburst episodes and phases of
suppressed star formation, potentially even causing temporary quiescence —
so-called mini-quenching events. However, the regime of star-formation
burstiness is observationally highly unconstrained. Directly observing
mini-quenched galaxies in the primordial Universe is therefore of utmost
importance to constrain models of galaxy formation and transformation. Early
quenched galaxies have been identified out to redshift $z<5$, and these are all
found to be massive ($M_{*}>10^{10}~M_{odot}$) and relatively old. Here we
report a (mini-)quenched galaxy at z$=$7.3, when the Universe was only 700~Myr
old. The JWST/NIRSpec spectrum is very blue ($U$-$V$$=$0.16$pm0.03$~mag), but
exhibits a Balmer break and no nebular emission lines. The galaxy experienced a
short starburst followed by rapid quenching; its stellar mass (4-6$times
10^8~M_odot$) falls in a range that is sensitive to various feedback
mechanisms, which can result in perhaps only temporary quenching.
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