Discovery of a new N-emitter in the epoch of reionization

Abstract: We report the discovery of a compact star-forming galaxy at $z=9.380$ in the GOODS-North field (named GN-z9p4) which shows numerous strong UV-optical emission lines and a single UV line, NIV] 1486. This makes GN-z9p4 the third-highest redshift N-emitter known to date. We determine the nebular abundances of H, C, N, O and Ne, size, and other physical properties of this object, and compare them to those of the other N-emitters known so far and to other star-forming galaxies. Using the direct method we find a metallicity 12+log(O/H)$=7.37 \pm 0.15$, one of the lowest among the N-emitters. The N/O abundance ratio is highly super-solar, and C/O and Ne/O normal compared to other galaxies at low metallicity. We show that the compactness of GN-z9p4 (with effective radius $118\pm16$ pc at 2 micron) and other N-emitters translates into very high stellar mass and SFR surface densities, which could be a criterium to identify other N-emitters. Future studies and larger samples are needed to understand these recently discovered, rare, and enigmatic objects.