  Finding the first generation of stars formed out of pristine gas in the early
Universe, known as Population III (PopIII) stars, is one of the most important
goals of modern astrophysics. Recent models suggest that PopIII stars may form
in pockets of pristine gas in the halo of more evolved galaxies. Here we
present NIRSpec-IFU and NIRSpec-MSA observations of the region around GN-z11,
an exceptionally luminous galaxy at $z=10.6$, which reveal a $>$5$\sigma$
detection of a feature consistent with being HeII$\lambda$1640 emission at the
redshift of GN-z11. The very high equivalent width of the putative HeII
emission in this clump (170 A), and the lack of metal lines, can be explained
in terms of photoionisation by PopIII stars, while photoionisation by PopII
stars is inconsistent with the data. It would also indicate that the putative
PopIII stars likely have a top-heavy initial mass function (IMF), with an upper
cutoff reaching at least 500 M$_\odot$. The PopIII bolometric luminosity
inferred from the HeII line would be $\sim 2\times 10^{10}~L_\odot$, which
(with a top-heavy IMF) would imply a total stellar mass formed in the burst of
$\sim 6\times 10^{5}~M_\odot$. We find that photoionisation by the Active
Galactic Nucleus (AGN) in GN-z11 cannot account for the HeII luminosity
observed in the clump, but can potentially be responsible for additional HeII
emission observed closer to GN-z11. We also consider the possibility of in-situ
photoionisation by an accreting Direct Collapse Black Hole (DCBH) hosted by the
HeII clump; we find that this scenario is less favoured, but it remains a
possible alternative interpretation. We also report the detection of a
Ly$\alpha$ halo stemming out of GN-z11 and extending out to $\sim$2 kpc, as
well as resolved, funnel-shaped CIII] emission, likely tracing the ionisation
cone of the AGN.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics