We analyze new JWST NIRCam and NIRSpec data on the redshift 9.11 galaxy
MACS1149-JD1. Our NIRCam imaging data reveal that JD1 comprises three spatially
distinct components. Our spectroscopic data indicate that JD1 appears dust-free
but is already enriched, 12+log(O/H)=7.90−0.05+0.04. We
also find that the Carbon and Neon abundances in JD1 are below the solar
abundance ratio. Particularly the Carbon under-abundance is suggestive of
recent star formation where Type~II supernovae have already enriched the ISM in
Oxygen but intermediate mass stars have not yet enriched the ISM in Carbon. A
recent burst of star formation is also revealed by the star formation history
derived from NIRCam photometry. Our data do not reveal the presence of a
significant amount of old populations, resulting in a factor of ∼7×
smaller stellar mass than previous estimates. Thus, our data support the view
that JD1 is a young galaxy.Comment: Accepted for publicatio