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Arxiv: Deep rest-UV JWST/NIRSpec spectroscopy of early galaxies: the demographics of CIV and N-emitters in the reionization era Published: 7/26/2024 9:00:03 PM Updated: 7/26/2024 9:00:03 PM

Paper abstract: JWST has recently discovered a subset of reionization era galaxies withionized gas that is metal poor in oxygen and carbon but heavily-enriched innitrogen. This abundance pattern is almost never seen in lower redshiftgalaxies but is commonly observed in globular cluster stars. We have recentlydemonstrated that this peculiar abundance pattern appears in a compact (~eq20 pc) metal-poor galaxy undergoing a strong burst of star formation. Thisgalaxy was originally selected based on strong CIV emission, indicating a hardradiation field rarely seen locally. In this paper, we present JWST/NIRSpecobservations of another reionization-era galaxy known to power strong CIVemission, the z=7.04 gravitationally-lensed galaxy A1703-zd6. The emissionline spectrum reveals this is a metal poor galaxy (12+\log(\rm O/H) =7.47\pm0.19) dominated by a young stellar population (1.6^{+0.5}_{-0.4} Myr)that powers a very hard ionizing spectrum (CIV EW = 19.4 \unicode{x212B}, HeII EW = 2.2 \unicode{x212B}). The ISM is highly-enriched in nitrogen(\log(\rm N/O)=-0.6) with very high electron densities (8-19\times10^4cm^{-3}) and extreme ionization conditions rarely seen at lower redshift. Wealso find intense CIV emission (EW\gtrsim20 \unicode{x212B}) in two newz\gtrsim 6 metal poor galaxies. To put these results in context, we searchfor UV line emission in a sample of 737 z\gtrsim 4 galaxies with NIRSpecspectra, establishing that 40(30)% of systems with [OIII]+H\beta EW>2000\unicode{x212B} have NIV] (CIV) detections with EW>5 \unicode{x212B}(>10 \unicode{x212B}). These results suggest high N/O ratios and hardionizing sources appear in a brief phase following a burst of star formation incompact high density stellar complexes.