Kavli Affiliate: Robert A. Simcoe
| First 5 Authors: Rohan P. Naidu, Pascal A. Oesch, Gabriel Brammer, Andrea Weibel, Yijia Li
| Summary:
JWST has revealed a stunning population of bright galaxies at surprisingly
early epochs, $z>10$, where few such sources were expected. Here we present the
most distant example of this class yet — MoM-z14, a luminous
($M_{rm{UV}}=-20.2$) source in the COSMOS legacy field at
$z_{rm{spec}}=14.44^{+0.02}_{-0.02}$ that expands the observational frontier
to a mere 280 million years after the Big Bang. The redshift is confirmed with
NIRSpec/prism spectroscopy through a sharp Lyman-$alpha$ break and
$approx3sigma$ detections of five rest-UV emission lines. The number density
of bright $z_{rm{spec}}approx14-15$ sources implied by our "Mirage or
Miracle" survey spanning $approx350$ arcmin$^{2}$ is $>100times$ larger
($182^{+329}_{-105}times$) than pre-JWST consensus models. The high EWs of UV
lines (${approx}15{-}35$ AA) signal a rising star-formation history, with a
${approx}10times$ increase in the last 5 Myr
($rm{SFR_{rm{5Myr}}}/rm{SFR_{rm{50Myr}}}=9.9^{+3.0}_{-5.8}$). The source is
extremely compact (circularized $r_{rm{e}} = 74^{+15}_{-12}$ pc), and yet
resolved, suggesting an AGN is not the dominant source of light. The steep UV
slope ($beta=-2.5^{+0.2}_{-0.2}$) implies negligible dust attenuation and a
young stellar population. The absence of a strong damping wing may indicate
that the immediate surroundings of MoM-z14 are partially ionized at a redshift
where virtually every reionization model predicts a $approx100%$ neutral
fraction. The nitrogen emission and highly super-solar [N/C]$>1$ hint at an
abundance pattern similar to local globular clusters that may have once hosted
luminous supermassive stars. Since this abundance pattern is also common among
the most ancient stars born in the Milky Way, we may be directly witnessing the
formation of such stars in dense clusters, connecting galaxy evolution across
the entire sweep of cosmic time.
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