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Using JWST/NIRSpec prism data from CEERS, JADES, RUBIES, and CAPERS, this study classifies 61 CIII]λ1907,1909-emitting galaxies at z=5–7 and finds that at least 29 (≈48%) show secure AGN signatures via UV/optical diagnostics or broad Balmer lines. The CIII] equivalent width (EW) at z=5–7 has a median of 22.8 Å — nearly five times higher than the 4.7 Å median at z=3–4 — representing a ~0.67 dex increase over the same UV luminosity range, signaling strong redshift evolution in ionization conditions. The optical OHNO diagram is flagged as a low-efficiency AGN/SFG separator at these redshifts, while UV diagnostics (CIII]/HeII and CIV/HeII) prove more discriminating. Five sources are identified as Little Red Dots (LRDs), one of which is newly reported.
A JWST NIRSpec spectroscopic study of photometrically selected extreme emission-line galaxies (EELGs) in the CEERS field — drawing on CAPERS, RUBIES, THRILS, and CEERS surveys — finds that AGN are not the dominant source of extreme ionizing radiation in the early Universe. While ~10% of photometrically selected EELGs show broad Balmer lines (a signature of AGN), deep spectroscopy raises this to ~35%, indicating significant AGN contamination in photometric samples. Critically, even in confirmed AGN hosts, the narrow Hα component dominates over the broad component at the highest equivalent widths, confirming that star formation — not AGN activity — is the primary engine of extreme emission.