Topping, MW, Stark, DP, Senchyna, P, Chen, Z, Zitrin, A, Endsley, R, Charlot, S, Furtak, LJ, Maseda, MV, Plat, A, Smit, R, Mainali, R, Chevallard, J, Molyneux, S and Rigby, JR (2025) Deep Rest-UV JWST/NIRSpec Spectroscopy of Early Galaxies: The Demographics of C iv and N-emitters in the Reionization Era. The Astrophysical Journal, 980 (2). pp. 1-31. ISSN 0004-637X

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Abstract

JWST has recently discovered a subset of reionization era galaxies with ionized gas that is metal-poor in oxygen and carbon but heavily enriched in nitrogen. This abundance pattern is almost never seen in lower-redshift galaxies but is commonly observed in globular cluster stars. We have recently demonstrated that this peculiar abundance pattern appears in a compact (≃20 pc) metal-poor galaxy undergoing a strong burst of star formation. This galaxy was originally selected based on strong C iv emission, indicating a hard radiation field rarely seen locally. In this paper, we present JWST/NIRSpec observations of another reionization-era galaxy known to power strong C iv emission, the z = 7.04 gravitationally lensed galaxy A1703-zd6. The emission-line spectrum reveals this is a metal-poor galaxy ((12 + log O/H = 7.47 + 0.19 ) dominated by a young stellar population ( 1.6 +0.5 -0.4 Myr) that powers a very hard ionizing spectrum (C iv equivalent width, EW = 19.4 Å, He ii EW = 2.2 Å). The interstellar medium is highly enriched in nitrogen ((C IV equivalent width, EW = 19.4 Å, He II EW = 2.2 Å) with very high electron densities (8–19 × 104 cm−3) and extreme ionization conditions rarely seen at lower redshift. We also find intense CIV emission (EW ≳ 20 Å) in two new z ≳ 6 metal-poor galaxies. To put these results in context, we search for UV line emission in a sample of 737 z ≳ 4 galaxies with NIRSpec spectra, establishing that 40%(30%) of systems with [O iii]+Hβ EW > 2000 Å have N iv] (C iv) detections with EW > 5 Å(> 10 Å). These results suggest high N/O ratios, and hard ionizing sources appear in a brief phase following a burst of star formation in compact high-density stellar complexes.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
SWORD Depositor:	A Symplectic
Date Deposited:	10 Apr 2025 08:40
Last Modified:	10 Apr 2025 08:45
DOI or ID number:	10.3847/1538-4357/ada95c
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26147

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