JADES NIRSpec Spectroscopy of GN-z11: Lyman-alpha emission and possible enhanced nitrogen abundance in a z = 10.60 luminous galaxy

We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous candidate $z > 10$ Lyman break galaxy in the GOODS-North field with $M_{\mathrm{UV}} = -21.5$ . 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 $0.7-5.3\ \mu\mathrm{m}$ . We significantly detect the continuum and measure a blue rest-UV spectral slope of $\beta = -2.4$ . Remarkably, we see spatially extended Lyman-$\alpha$ in emission (despite the highly neutral intergalactic medium expected at this early epoch), offset $555\ \mathrm{km/s}$ redwards of the systemic redshift. From our measurements of collisionally excited lines of both low and high ionisation (including $\mathrm{[OII]}\lambda3727$ , $\mathrm{[NeIII]}\lambda3869$ , and $\mathrm{CIII]}\lambda1909$ ), we infer a high ionisation parameter ($\mathrm{log}_{10}(U) \sim -2$ ). We detect the rarely seen $\mathrm{NIV]}\lambda1486$ and $\mathrm{NIII]}\lambda1748$ lines in both our low and medium resolution spectra, with other high ionisation lines seen in the low resolution spectrum, such as $\mathrm{HeII}$ (blended with $\mathrm{OIII]}$ ) and $\mathrm{CIV}$ (with a possible P-Cygni profile). Based on the observed rest-UV line ratios, we cannot conclusively rule out photoionisation from an active galactic nucleus (AGN), although the high $\mathrm{CIII]/HeII}$ and $\mathrm{NIII]/HeII}$ ratios are compatible with a star formation explanation. If the observed emission lines are powered by star formation, then the strong $\mathrm{NIII]}\lambda1748$ observed may imply an unusually high $\mathrm{N/O}$ abundance. Balmer emission lines ($\mathrm{H}\gamma$ , $\mathrm{H}\delta$ ) are also detected, and if powered by star formation rather than an AGN, we infer a star formation rate of $\sim 20-30\ M_{\odot}/\mathrm{yr}$ (depending on the initial mass function) 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.

Astronomy & Astrophysics, Volume 677, id.A88, 17 pages