Аннотация
The first stars, known as Population III (PopIII), produced the first heavy
elements, thereby enriching their surrounding pristine gas. Previous detections
of metals in intergalactic gas clouds, however, find a heavy element enrichment
larger than $1/1000$ times that of the solar environment, higher than expected
for PopIII remnants. In this letter we report the discovery of a Lyman limit
system (LLS) at $z=3.53$ with the lowest metallicity seen in gas with
discernable metals, $10^-3.41\pm0.26$ times the solar value, at a level
expected for PopIII remnants. We make the first relative abundance measurement
in such low metallicity gas: the carbon-to-silicon ratio is $10^-0.26\pm0.17$
times the solar value. This is consistent with models of gas enrichment by a
PopIII star formation event early in the Universe, but also consistent with
later, Population II enrichment. The metals in all three components comprising
the LLS, which has a velocity width of 400 km s$^-1$, are offset in velocity
by $\sim+6$ km s$^-1$ from the bulk of the hydrogen, suggesting the LLS was
enriched by a single event. Relative abundance measurements in this
near-pristine regime open a new avenue for testing models of early gas
enrichment and metal mixing.
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