JADES NIRSpec Spectroscopy of GN-z11: Lyman-$\hat{I}\pm$ emission and possible enhanced nitrogen abundance in a $z=10.60$ luminous galaxy

Abstract

We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous candidate $z>10$ Lyman break galaxy in the GOODS-North field with $M_{UV}=-21.5$. We derive a redshift of $z=10.603$ (lower than previous determinations) based on multiple emission lines in our low and medium resolution spectra over $0.8-5.3\hat{I}¼$m. We significantly detect the continuum and measure a blue rest-UV spectral slope of ${\hat{I}}^2=-2.4$. Remarkably, we see spatially-extended Lyman-$\hat{I}\pm$ in emission (despite the highly-neutral IGM expected at this early epoch), offset 555 km s${}^{-1}$ redward of the systemic redshift. From our measurements of collisionally-excited lines of both low- and high-ionization (including [O II]$\lambda 3727$, [Ne III]$\hat{I}»3869$ and C III]$\lambda 1909$) we infer a high ionization parameter ($\log U\sim -2$). We detect the rarely-seen N IV]$\lambda 1486$ and N III]$\lambda 1748$ lines in both our low and medium resolution spectra, with other high ionization lines seen in the low resolution spectrum such as He II (blended with O III]) and C IV (with a possible P-Cygni profile). Based on the observed rest-UV line ratios, we cannot conclusively rule out photoionization from AGN, although the high C III]/He II and N III]/He II ratios are compatible with a star-formation explanation. If the observed emission lines are powered by star formation, then the strong N III]$\lambda 1748$ observed may imply an unusually high $N/O$ abundance. Balmer emission lines (H${\hat{I}}^3$, H$\hat{I}´$) are also detected, and if powered by star formation rather than an AGN we infer a star formation rate of $\sim 20-30M_{\odot }y{r}^{-1}$ (depending on the IMF) and low dust attenuation. Our NIRSpec spectroscopy confirms that GN-z11 is a remarkable galaxy with extreme properties seen 430 Myr after the Big Bang.

Accepted for publication in Astronomy & Astrophysics, 17 pages, 12 figures. Line fluxes updated