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The first stars, known as Population III, produced the first heavy elements, thereby enriching their surrounding pristine gas. However, all previous detections of metals in intergalactic gas clouds find a heavy element enrichment at least 1/1000 times that of the solar environment, which is higher than expected for remnants of Population III stars. In this talk I will describe our search for gas clouds with enrichment levels below this metallicity ’floor’ of 1/1000th solar, and outline the challenges involved in finding such systems and measuring their metallicity. Our search has discovered a cloud at redshift 3.5 with metallicity 1/2500th solar, the lowest value yet seen in a single cloud containing metals, and at the level expected for Population III remnants. I will discuss how relative abundance measurements in this extremely metal-poor regime enable us to test models of Population III star formation, early gas enrichment and metal mixing. Finally, I will summarise the prospects for finding similar systems in future surveys. |
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