We present JADES JWSTNIRSpec spectroscopy of GNz11 the most luminous candidate z gt 10 Lyman break galaxy in the GOODSNorth field with MSUBUVSUB  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 m. We significantly detect the continuum and measure a blue restUV spectral slope of   2.4. Remarkably we see spatially extended Lyman in emission despite the highly neutral intergalactic medium expected at this early epoch offset 555 km sSUP1SUP redwards of the systemic redshift. From our measurements of collisionally excited lines of both low and high ionisation including O II 3727 Ne III 3869 and C III 1909 we infer a high ionisation parameter log U  2. We detect the rarely seen N IV 1486 and N III 1748 lines in both our low and medium resolution spectra with other high ionisation lines seen in the low resolution spectrum such as He II blended with O III and C IV with a possible PCygni profile. Based on the observed restUV line ratios we cannot conclusively rule out photoionisation from an active galactic nucleus AGN although the high C IIIHe II and N IIIHe II ratios are compatible with a star formation explanation. If the observed emission lines are powered by star formation then the strong N III 1748 observed may imply an unusually high NO abundance. Balmer emission lines H H are also detected and if powered by star formation rather than an AGN we infer a star formation rate of 20  30 MSUBSUB yrSUP1SUP depending on the initial mass function and low dust attenuation. Our NIRSpec spectroscopy confirms that GNz11 is a remarkable galaxy with extreme properties seen 430 Myr after the Big Bang.
['galaxies: high-redshift', 'galaxies: evolution', 'galaxies: groups: individual: GN-z11', 'galaxies: abundances', 'Astrophysics - Astrophysics of Galaxies', 'Astrophysics - Cosmology and Nongalactic Astrophysics']
JADES NIRSpec Spectroscopy of GNz11 Lyman emission and possible enhanced nitrogen abundance in a z  10.60 luminous galaxy
{'JADES NIRSpec Spectroscopy of GN-z11: LymanGLYPH<11> emission and possible enhanced nitrogen abundance in a z = 10 : 60 luminous galaxy': "Andrew J. Bunker 1, ? , Aayush Saxena 1,2 , Alex J. Cameron 1 , Chris J. Willott 3 , Emma Curtis-Lake 4 , Peter Jakobsen 5,6 , Stefano Carniani 7 , Renske Smit 8 , Roberto Maiolino 9,10,2 , Joris Witstok 9,10 , Mirko Curti 9,10,11 , Francesco D'Eugenio 9,10 , Gareth C. Jones 1 , Pierre Ferruit 12 , Santiago Arribas 13 , Stephane Charlot 14 , Jacopo Chevallard 1 , Giovanna Giardino 15 , Anna de Graa GLYPH<11> 16 , Tobias J. Looser 9,10 , Nora Lützgendorf 17 , Michael V. Maseda 18 , Tim Rawle 17 , Hans-Walter Rix 16 , Bruno Rodríguez Del Pino 13 , Stacey Alberts 19 , Eiichi Egami 19 , Daniel J. Eisenstein 20 , Ryan Endsley 21 , Kevin Hainline 19 , Ryan Hausen 22 , Benjamin D. Johnson 20 , George Rieke 19 , Marcia Rieke 19 , Brant E. Robertson 23 , Irene Shivaei 19 , Daniel P. Stark 19 , Fengwu Sun 19 , Sandro Tacchella 9,10 , Mengtao Tang 19 , Christina C. Williams 24,19 , Christopher N. A. Willmer 19 , William M. Baker 9,10 , Stefi Baum 25 , Rachana Bhatawdekar 12,26 , Rebecca Bowler 27 , Kristan Boyett 28,29 , Zuyi Chen 19 , Chiara Circosta 12 , Jakob M. Helton 19 , Zhiyuan Ji 19 , Jianwei Lyu 19 , Erica Nelson 30 , Eleonora Parlanti 7 , Michele Perna 13 , Lester Sandles 9,10 , Jan Scholtz 9,10 , Katherine A. Suess 23,31 , Michael W. Topping 19 , Hannah Übler 9,10 , Imaan E. B. Wallace 1 , and Lily Whitler 19  \n(A GLYPH<14> liations can be found after the references)", '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 MUV = GLYPH<0> 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 GLYPH<0> 5 : 3 GLYPH<22> m. We significantly detect the continuum and measure a blue rest-UV spectral slope of GLYPH<12> = GLYPH<0> 2 : 4. Remarkably, we see spatially-extended LymanGLYPH<11> in emission (despite the highly-neutral IGM expected at this early epoch), o GLYPH<11> set 555 km s GLYPH<0> 1 redward of the systemic redshift. From our measurements of collisionally-excited lines of both low- and high-ionization (including [O ii ] GLYPH<21> 3727, [Ne iii ] GLYPH<21> 3869 and C iii ] GLYPH<21> 1909) we infer a high ionization parameter (log U GLYPH<24> GLYPH<0> 2). We detect the rarely-seen N iv ] GLYPH<21> 1486 and N iii ] GLYPH<21> 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 ] GLYPH<21> 1748 observed may imply an unusually high N = O abundance. Balmer emission lines (H GLYPH<13> , H GLYPH<14> ) are also detected, and if powered by star formation rather than an AGN we infer a star formation rate of GLYPH<24> 20 GLYPH<0> 30 M GLYPH<12> yr GLYPH<0> 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.  \nKey words. Galaxies: high-redshift - Galaxies: formation - Galaxies: active - (Cosmology:) dark ages, reionization, first stars', '1. Introduction': 'Spectroscopically confirming galaxies formed within the first few hundred million years after the Big Bang, and understanding their nature and evolution, represents one of the biggest challenges of modern astrophysics, and one of the main drivers behind the James Webb Space Telescope (JWST) . Probing the formation of some of the very first galaxies helps establish the epoch of first light in the Universe, i.e. the timescales of the formation of the first stars, bringing an end to the so-called cosmic Dark Ages. Deep NIRSpec follow-up of some of the highest redshift galaxy candidates has already yielded spectroscopic confirmations via clear detection of the Lyman break in four galaxies at z > 10 (Curtis-Lake et al. 2023; Robertson et al. 2023).  \nThe onset of the first star formation began the process of reionizing the intergalactic medium (IGM), although the exact details of this reionization are still uncertain. Observations of LymanGLYPH<11> emission and absorption provide strong constraints on  \nhow and when the di GLYPH<11> use gas in the IGM transitions from neutral to ionized (see Robertson 2022 for a review). An important observation is the decrease in LymanGLYPH<11> emission line equivalent width with increasing redshift above z = 6 (Stark et al. 2010; Schenker et al. 2014; Caruana et al. 2014; Jung et al. 2020), consistent with stronger absorption from an increasingly neutral IGM. However, this picture was largely based on moderateluminosity galaxies. Luminous galaxies at 7 : 5 < z < 9 often show LymanGLYPH<11> emission (Zitrin et al. 2015; Oesch et al. 2015; Stark et al. 2017; Larson et al. 2022; Finkelstein et al. 2013; Roberts-Borsani et al. 2016; Jung et al. 2019; Song et al. 2016), at a redshift where quasar damping wing studies suggest the IGM is significantly neutral ( x hi GLYPH<24> 0 : 5; Greig et al. 2017; Davies et al. 2018; Wang et al. 2020). This indicates that around luminous (and potentially massive) galaxies, LymanGLYPH<11> escapes more easily, perhaps as a result of ionized bubbles that grew early in overdense regions (Endsley & Stark 2022; Jung et al. 2022; cf. Saxena et al. 2023). Another possible LymanGLYPH<11> escape mechanism is through resonant scattering, with high velocity neutral  \ngas (perhaps associated with outflows) redshifting the photons to lower frequencies at which they are no longer absorbed by the intervening neutral IGM (Dijkstra 2014; Mason et al. 2018a). Deep spectroscopy with JWST is vastly increasing our knowledge in this area, both by detecting rest-frame optical lines of known LymanGLYPH<11> emitters to derive systemic redshifts and details of nebular physical conditions, and by detecting LymanGLYPH<11> further into the reionization epoch than has been possible from the ground (e.g. Tang et al. 2023).  \nBefore the launch of JWST , the most distant galaxy with a tentative but plausible spectroscopic redshift was GN-z11 (Oesch et al. 2016). This was first selected as a likely high redshift Lyman-break candidate through multi-colour imaging with HST (Bouwens et al. 2010; Oesch et al. 2015), and subsequent HST / WFC3 slitless grism spectroscopy revealed a possible Lyman break in the continuum (Oesch et al. 2016), yielding a redshift of z grism = 11 : 09. With an apparent H 160 magnitude of 26 : 0 GLYPH<6> 0 : 1, GN-z11 is remarkably bright, up to 3 times more luminous than the characteristic rest-UV luminosity ( L ? ) measured from luminosity functions at z GLYPH<24> 6 GLYPH<0> 8 (e.g. Finkelstein et al. 2015; Bouwens et al. 2015). Using Spitzer / IRAC fluxes, Oesch et al. (2016) estimated its stellar mass to be M ? = 10 9 M GLYPH<12> , indicating a rapid build up of stellar mass in the very early Universe.  \nThrough ground-based near-infrared spectroscopy using MOSFIRE on the Keck Telescope, the redshift of GN-z11 was further refined by Jiang et al. (2021) via the possible detection of the [C iii ] GLYPH<21> 1907 + C iii ] GLYPH<21> 1909 doublet, yielding a redshift of z = 10 : 957. If real, the intense C iii ] emission line might originate partly due to an active galactic nucleus (AGN) hosted by the galaxy, or due to rapid carbon enrichment (Jiang et al. 2021).  \nGiven the unique nature of this source and the low signal-tonoise ratio ( S = N ) of existing continuum break and emission line detections of this galaxy, NIRSpec on JWST now o GLYPH<11> ers a chance to confirm its true distance and nature through high S = N detection of multiple rest-UV and optical emission lines as well as its bright continuum. Several diagnostics relying on the ratios and strengths of rest-UV and optical emission lines can help di GLYPH<11> erentiate between photoionization due to AGN or star-formation alone, and further help characterize the ionization conditions in the interstellar medium (ISM) of this remarkably luminous distant galaxy.  \nIn this paper, we report an unambiguous spectroscopic redshift of z = 10 : 6034 for GN-z11 using deep NIRSpec observations in the GOODS-North field via the robust detection of several emission lines including N iv ] GLYPH<21> 1486, N iii ] GLYPH<21>GLYPH<21> 1747 ; 1749, [C iii ] GLYPH<21> 1907 + C iii ] GLYPH<21> 1909, [O ii ] GLYPH<21>GLYPH<21> 3726 ; 3729, [Ne iii ] GLYPH<21>GLYPH<21> 3869 ; 3967, H GLYPH<14> and H GLYPH<13> . Although the measured redshift is lower than previously reported in other work, this still places GN-z11 as comfortably the most luminous source currently confirmed at z > 10. This galaxy is given the designation JADES-GN-z10-0 in the JADES spectroscopic database, but for the remainder of this paper we use the more familiar name GN-z11. The photometric properties from our JWST / NIRCam imaging are reported in a companion paper (Tacchella et al. 2023).  \nThe layout of this paper is as follows. In Section 2 we describe our JWST / NIRSpec observations of GN-z11 and the data reduction strategies adopted. In Section 3 we present the 1D and 2D spectra of GN-z11, emission line measurements and discuss the inferred physical properties. In Section 4 we conclude our findings. Throughout this work, we assume the Planck 2018 cosmology (Planck Collaboration et al. 2020) and the AB magnitude system (Oke & Gunn 1983).', '2. Observations': 'The NIRSpec observations of GN-z11 were taken as part of the JWST Advanced Deep Extragalactic Survey (JADES), a collaboration between the Instrument Science Teams of NIRSpec and NIRCam to study galaxy evolution out to high redshift through imaging and spectroscopy in the two GOODS fields. The Guaranteed Time Observations presented here are part of program ID 1181 (P.I.: D. Eisenstein), with spectroscopic targets based on preJWST data, largely HST imaging.  \nOur observations of GN-z11 were taken on UT 5 & 7 February 2023, using NIRSpec (Jakobsen et al. 2022) in its microshutter array (MSA) mode (Ferruit et al. 2022). The MSA comprises four arrays of 365 GLYPH<2> 171 independently-operable shutters, each covering 98 00 GLYPH<2> 91 00 on the sky. GN-z11 was targeted in four independent MSA configurations. Each configuration acquired 3100 s of integration in each of the medium-resolution G140M / F070LP, G235M / F170LP, and G395M / F290LP grating / filter combinations (with resolving power R GLYPH<25> 1000 and combined spectral coverage over 0 : 7 GLYPH<0> 5 : 3 GLYPH<22> m) and 6200 s in the low-resolution PRISM / CLEAR mode (with R GLYPH<24> 100 and continuous coverage 0 : 7 GLYPH<0> 5 : 3 GLYPH<22> m). Targets were assigned three shutter slitlets, with the targets nodded into each of the three shutters during the observing sequence to facilitate background subtraction. As GN-z11 was one of our highest priority targets, we ensured that its spectra did not overlap with other targets, even for the gratings (where the spectra are more extended on the detector than the low-dispersion prism). Individual integrations used the NRSIRS2 readout mode with 14 groups (1035 s each) to limit correlated readout noise. In total our integration time was 3.45 hours in each of the three gratings, and 6.9 hours in the prism.  \nThese observations were processed with algorithms developed by the ESA NIRSpec Science Operations Team and the NIRSpec GTO Team. We refer the reader to Cameron et al. (2023) for more details of the processing. We note that for the G140M / F070LP grating / filter combination we extended the calibration of the spectrum up to 1.84 GLYPH<22> m, taking into account the transmission filter throughput beyond the nominal wavelength range of this configuration (0.70 GLYPH<22> m-1.27 GLYPH<22> m). Since GN-z11 is at z > 10 with no flux at wavelengths below LymanGLYPH<11> , there is no second order light to overlap with the extended wavelength range of 1.27 GLYPH<22> m-1.84 GLYPH<22> m. Wavelength-dependent path-loss corrections were made based on the object position within the shutter and modelling the galaxy as a point-like source. GN-z11 is very compact, so this is a good approximation. In all four of the configurations, GN-z11 was located not more than 40% of the illuminated slit width or slit height from the centre along either axis of the 0 00 : 20 GLYPH<2> 0 00 : 46 slitlet, and Figure 1 shows the locations of the open areas of the microshutters overlaid on the NIRCam F200W image of GN-z11. Individual calibrated one-dimensional (1D) and 2D spectra were combined excluding bad pixels by using an an iterative sigma clipping algorithm at the 3 GLYPH<27> level. The wavelength calibration takes into account the position of the galaxy within the slit at each pointing. Before the combination process a spatial median of each exposure is subtracted to remove any residual background. 1D spectral extractions were made from the rectified 2D spectra using box extractions of height 3 and 5 pixels (0 00 : 3 and 0 00 : 5, respectively).', '3. Results': 'Our NIRSpec spectra of GN-z11 show well-detected continuum in the prism (Figure 2) where we have S = N > 20 per  \nFig. 1. The NIRCam F200W image of GN-z11 (see Tacchella et al. 2023) with the NIRSpec microshutters overlaid for the four di GLYPH<11> erent pointings. The green rectangles denote the illuminated region of each microshutter (0 00 : 2 GLYPH<2> 0 00 : 46). North is up and East to the left, and the image is 3 arcsec on the side. The flux density units on the colour bar are MJy / sr.  \n<!-- image -->  \nspectral resolution element at wavelength above LymanGLYPH<11> and out to GLYPH<24> 3 GLYPH<22> m. We also see the continuum at lower S = N in the medium-resolution gratings (Figure 3, Figure B.1). A strong spectral break at LymanGLYPH<11> is observed, with no significant flux at shorter wavelengths. We have robust detections of several emission lines, most of which are seen in both the prism (Figure 2) and grating (Figure 3) spectra. We also see evidence of interstellar absorption lines, but in this paper we focus on the emission lines properties.  \nIn the subsections below, we use the spectrum of GN-z11 to infer physical properties. As well as using empirical diagnostics from the emission line fluxes and ratios, we also use the beagle Bayesian SED fitting code (Chevallard & Charlot 2016) on our full prism spectrum, the exact details and results are presented in Table 2 and in Appendix A.', '3.1. Emission lines and Redshift Determination': 'The full list of detected lines is given in Table 1. Line wavelengths are measured from the grating spectra because they have higher resolution resulting in less blending and more accurate line centroids. Line fluxes are measured from both the prism and gratings, and we discuss the relative flux calibration between the two in Appendix C. We perform a cubic-spline fit to the continuum in the prism (excluding the emission lines from the fit), and use this to subtract the continuum level in both the prism and the grating spectra (since the continua in the grating spectra have low signal-to-noise ratio). We then fit each emission line with a single Gaussian model, except for blended lines (noted in Table 1) where we measure the total flux of the complex. The uncertainty is computed taking into account the Poisson  \ncounting statistics and the readout noise. This is preferred to taking the intra-pixel standard deviation in counts in the spectrum, which would underestimate the true noise since the pixels are sub-sampled and interpolated from their native size by the data reduction pipleline and hence the noise is correlated. One emission line, N iv ] GLYPH<21> 1486, falls in the spectral coverage of both the G140M and G235M gratings, and we report both measurements in Table 1. The wavelength and flux of this line are consistent between the gratings within the uncertainties.  \nIn determining the redshift from the vacuum rest-frame wavelengths, we exclude LymanGLYPH<11> (which has a velocity o GLYPH<11> -set, see Section 3.3), Mg ii (which is only significantly detected in the low-resolution prism) and He i GLYPH<21> 3889 (which is blended with Balmer-8). A weighted fit of the remaining 8 well-detected emission lines ( S = N > 5) from the grating spectra give a redshift z = 10 : 6034 GLYPH<6> 0 : 0013, where we assume a [C iii ] GLYPH<21> 1907 / C iii ] GLYPH<21> 1909 doublet ratio of 1 : 5 for these spectrally-unresolved lines.  \nThe redshift we measure is considerably lower than the previously reported redshift values of z = 11 : 09 + 0 : 08 GLYPH<0> 0 : 012 from HST grism (Oesch et al. 2016) and z = 10 : 957 GLYPH<6> 0 : 001 from Keck MOSFIRE (Jiang et al. 2021). The 2D HST grism observation shows flux down to the wavelength we measure for the Lyman break (1 : 41 GLYPH<22> m), but due to noise fluctuations their fitted model break was at a longer wavelength of 1 : 47 GLYPH<22> m. The Keck MOSFIRE redshift was based on possibles detections of the [C iii ] GLYPH<21> 1907 and C iii ] GLYPH<21> 1909 lines at 2 : 2797 GLYPH<22> m and 2 : 282 GLYPH<22> m respectively, at 2 : 6 GLYPH<27> and 5 : 3 GLYPH<27> . We do not find any significant emission lines at these observed wavelengths in our data, where they would have been detected at 20 GLYPH<27> and 40 GLYPH<27> for the line fluxes quoted in Jiang et al. (2021). Instead, we do detect C iii ] but at a shorter wavelength consistent with our measured z = 10 : 603.', '3.2. Is GN-z11 an AGN?': 'GN-z11 has a compact morphology and the continuum spatial extent in our NIRSpec 2D spectroscopy is barely resolved. In a companion paper, Tacchella et al. (2023) analyze JADES NIRCam imaging data and derive the best size constraint so far, finding an intrinsic half-light radius of only 0 : 016 GLYPH<6> 0 : 005 00 (64 GLYPH<6> 20 pc). The possibility of a significant point source contribution to the total flux leaves open the question of whether some of the light originates from an AGN. Our data do contain several high ionization lines and we wish to explore the excitation mechanism.  \nWe have detected a large number of emission lines of varying ionization potential in GN-z11. In particular the N iv ] GLYPH<21> 1486 line (ionization potential E > 47 : 5 eV) is often a signature of an AGN, although it has been seen in some high-redshift star forming galaxies (e.g., Fosbury et al. 2003 and McGreer et al. 2018) and it is detected in 6 of 44 galaxies in the low-redshift CLASSY survey (Mingozzi et al. 2022). N iv ] GLYPH<21> 1486 or N iii ] GLYPH<21> 1748 is seen in 1% of SDSS quasars at 1 : 7 < z < 4 : 0 (Jiang et al. 2008). Vanzella et al. (2010) detect N iv ] GLYPH<21> 1486 in an object at z = 5 : 6 which may be an AGN, although Raiter et al. (2010) are able to model this spectrum with stars. For GN-z11, the higher ionization Nitrogen line N v ( E > 77 : 5 eV), which is a clear signature of AGN activity, is undetected in the G140M grating (where the 3 GLYPH<27> sensitivity is 4 GLYPH<2> 10 GLYPH<0> 19 erg cm GLYPH<0> 2 s GLYPH<0> 1 ), and is blended with LymanGLYPH<11> continuum break at the prism resolution.  \nWe note that in the prism ( R GLYPH<24> 100) spectrum we see prominent emission features arising from blended He ii and [O iii ] GLYPH<21>GLYPH<21> 1660 ; 1666 lines, as well as a P-Cygni type feature from  \nFig. 2. 2D (top) and 1D (bottom) spectra of GN-z11 using PRISM / CLEAR configuration of NIRSpec. The 1D spectrum has been extracted using a 3 pixel wide aperture that leads to improved S / N in this highly compact object. Prominent emission lines present in the spectra are marked. The signal to noise ratio (SNR) of the continuum is high and the emission lines are clearly seen in both the 1D and 2D spectra.  \n<!-- image -->  \nC iv (see Figure 3), with redshifted emission and blueshifted absorption relative to the systemic redshift. civ emission with a PCygni-like profile is also detected in the grating, along with a low S = N tentative detection (3 GLYPH<27> ) of of He ii and [O iii ] GLYPH<21>GLYPH<21> 1660 ; 1666.  \nThe reliable detection of C iii ] and N iii ] lines in the grating spectra, however, enables us to investigate rest-UV line ratios that can be compared with predictions from photoionization models to di GLYPH<11> erentiate between an AGN or a star-formation origin (e.g. Feltre et al. 2016). In Figure 4 we plot the line ratios C iii ] GLYPH<21> 1909 / He ii GLYPH<21> 1640 versus C iii ] GLYPH<21> 1909 / C iv GLYPH<21>GLYPH<21> 1548 ; 1550, along with predictions from photoionization models of Feltre et al. (2016) for type 2 AGN, and Gutkin et al. (2016) for star formation. We consider a density range of log( nH = cm GLYPH<0> 3 ) range of 2 GLYPH<0> 4, and metallicities in the range Z = 0 : 001 GLYPH<0> 0 : 002, corresponding to Z = Z GLYPH<12> = 0 : 066 GLYPH<0> 0 : 131 (based on Z GLYPH<12> = 0 : 0152 assumed by Feltre et al. 2016), which is consistent with the gasphase metallicity inferred from SED fitting using beagle (Section A), and the estimates from emission line ratios in Section 3.5.  \nWe find that neither AGN nor SFG model predictions are able to conclusively explain the observed line ratios in GNz11. As previously noted, there is C iv absorption visible in the spectrum, blueshifted from the systemic redshift. However, it is unclear how much of the nebular component of the C iv line flux is being attenuated by this blueshifted absorption as there is not enough S / N in the grating to disentangle the nebular and stellar components of C iv . If a significant amount of nebular C iv emission is also being absorbed, then the data point would move downwards on the y -axis in Figure 4.  \nAdditionally, using the C iii ] and He ii based diagnostics from Nakajima et al. (2018), we find that the observed strength of C iii ] emission and the C iii ] / He ii ratio once again lie between photoionization model predictions due to type-2 AGN and starformation. Nakajima et al. (2018) found a parameter space in their diagnostic plots where both AGN and star-forming models could overlap due to low metallicities and high C / O ratios, which is where the measurements from GN-z11 suggest it could lie. We note that when considering the photoionization models of Nakajima & Maiolino (2022), the limit on C iii ] / C iv we derive is compatible with the envelope of expectations from AGN over a range of metallicities.  \nAratio of N iii ] / He ii GLYPH<25> 3 : 3 is consistent with photoionization due to star-formation (e.g. Hirschmann et al. 2019), and interestingly, no type 2 AGN scenario in the models of Hirschmann et al. (2019) predicts a N iii ] / He ii ratio greater than 1. Composite models containing contribution from both AGN and star-formation can achieve N iii ] / He ii ratios GLYPH<24> 1, but only star-formation is favoured at ratios > 1.  \nOverall, we find that the C iii ] and N iii ] emission and their ratios with respect to He ii and C iv do not obviously favour photoionization due to AGN. However, the presence of other rare lines (e.g. N iv ]) that have previously been observed in the spectra of AGN makes ruling out the presence of an AGN less obvious (see Übler et al. 2023, for example). Given the expected extreme nature of GN-z11, together with a lack of any observational insights into the expected spectroscopic properties of AGN at z > 10, we are unable to draw definitive conclusions about the dominant source of photoionization in GN-z11.  \nFinally, we note that the grating spectra do not show obvious evidence for the presence of a broad component of permitted lines (see Figure 3), which would be ascribed to the Broad Line Region (BLR) of an AGN. This is not necessarily conclusive proof against the AGN scenario, as the BLR is often obscured along our line of sight in most AGN, however it is another element consistent with the lack of dominant contribution from an AGN.', '3.3. LymanGLYPH<11> Emission': 'The prism spectrum shows a near-total Gunn-Peterson trough at wavelengths below LymanGLYPH<11> , consistent with a highly neutral intervening IGM (Gunn & Peterson 1965). Although the spectral break is fairly sharp in wavelength at the low dispersion of the prism, we do see some evidence of a damping wing absorption.  \nIn spectra from the bluest G140M grating, an emission line is seen at 14132 Å, close to the sharp Lyman break observed with the prism. Taking the systemic redshift of GN-z11 to be z = 10 : 6034 (see Section 3.1), the rest-frame wavelength is 1217.92 Å, consistent with being LymanGLYPH<11> in emission, but with the line centroid redshifted by 555 GLYPH<6> 32 km s GLYPH<0> 1 (see Figure 5).  \nFig. 3. Gallery of the most prominent emission lines seen in the spectrum GN-z11 from the Medium resolution (R1000) gratings using a 3 pixel 1D spectral extraction.  \n<!-- image -->  \nFig. 4. Measured C iii ] / He ii vs C iii ] / C iv ratios for GN-z11 shown along with predictions from photoionization due to AGN (circles) and starformation (stars) from Feltre et al. (2016) and Gutkin et al. (2016) considering in the range of Z = Z GLYPH<12> = 0 : 066 GLYPH<0> 0 : 131 and gas densities in the range log( nH ) = cm GLYPH<0> 3 = 2 GLYPH<0> 4. Based on the observed line ratios neither photoionization from AGN or star-formation alone can conclusively explain the observations, placing GNz11 right between the model predictions from the two.  \n<!-- image -->  \nFig. 5. Velocity o GLYPH<11> set of the Ly GLYPH<11> emission line (blue solid line) compared with the H GLYPH<13> line (green dashed line). The Ly GLYPH<11> line is redshifted by 555 km s GLYPH<0> 1 compared to the redshift derived from other emission lines in the spectrum.  \n<!-- image -->  \nThis emission line is seen in all 12 of the individual G140M  \nTable 1. Emission line fluxes (in units of GLYPH<2> 10 GLYPH<0> 19 erg s GLYPH<0> 1 cm GLYPH<0> 2 ) detected in the prism ( R GLYPH<24> 100) and grating ( R GLYPH<24> 1000) spectra measured from both the 3 pixel and the 5 pixel extraction.  \ngrating exposures (in each of the 3 nod positions in the 4 MSA configurations), and is > 10 GLYPH<27> in the combined grating spectrum.  \nFigure 6 shows a close-up of the G140M spectral region around LymanGLYPH<11> . There is zero transmitted flux shortward of the systemic LymanGLYPH<11> wavelength. Any such flux would require an ionized bubble around the galaxy, but the lack of such flux rules out an optically-thin H II region around GN-z11 (e.g. Mason & Gronke 2020). The redshifted line is well approximated by a Gaussian, without significant asymmetry. We measure a FWHM of 566 GLYPH<6> 61 km s GLYPH<0> 1 , which is extended beyond the instrumental line spread function of GLYPH<25> 200 km s GLYPH<0> 1 (de Graa GLYPH<11> et al. in prep) for a compact source in the G140M grating at this wavelength. Removing the line spread function in quadrature suggests an intrinsic velocity spread of GLYPH<14> v FWHM = 530 GLYPH<6> 65 km s GLYPH<0> 1 .  \nIn the 2D spectrum of Figure 6 it is apparent that the LymanGLYPH<11> emission is more spatially extended than the continuum. Whilst the continuum flux is largely contained within 2 pixels (0.2 00 ), as expected based on the small size measured in our NIRCam imaging presented in Tacchella et al. (2023), the LymanGLYPH<11> emission extends further to the south-west. The LymanGLYPH<11> extension beyond the continuum is at least 2 pixels, corresponding to an extra 0.8 kpc. We note the LymanGLYPH<11> could extend further  \nsince the MSA shutters are only 5 pixels high, so beyond this region there is self-subtraction, but a visual check of the 2D spectrum without background subtraction did not show LymanGLYPH<11> in neighbouring shutters. A similar check on the extent of other well-detected lines in the grating spectra ([O ii ] and H GLYPH<13> ) shows that these lines have the same spatial profile as their nearby continuum.  \nThe fact that LymanGLYPH<11> is spatially extended is a remarkable result, which may be suggestive of a LymanGLYPH<11> halo. The presence of such haloes around individual star-forming galaxies has been reported at lower redshifts (e.g. Rauch et al. 2008; Wisotzki et al. 2016; Leclercq et al. 2017; Kusakabe et al. 2022) and we may be seeing the gas in the circum-galactic medium (CGM), from LymanGLYPH<11> fluorescence or shock heating.  \nUsing a 3 pixel (0 : 3 00 ) extraction aperture, the measured LymanGLYPH<11> flux is (1 : 51 GLYPH<6> 0 : 15) GLYPH<2> 10 GLYPH<0> 18 erg s GLYPH<0> 1 cm GLYPH<0> 2 , with a restframe equivalent width (with respect to the continuum longward of the LymanGLYPH<11> break) of EW0 = 12 Å. Using a larger \'fullshutter" extraction aperture of height 5 pixels (0 : 5 00 ) gives a significantly higher flux of (2 : 30 GLYPH<6> 0 : 19) GLYPH<2> 10 GLYPH<0> 18 erg s GLYPH<0> 1 cm GLYPH<0> 2 , and the rest-frame equivalent width rises to EW0 = 18 Å. The emission  \nFig. 6. Zoom in on the Ly GLYPH<11> emission line in the G140M 1D (lower) and 2D (upper) spectra. The grey dashed line shows the systemic wavelength of the Ly GLYPH<11> transition. The histogram (top-left) of the Ly GLYPH<11> spatial profile (yellow) and that of the continuum (blue), shows the Ly GLYPH<11> emission from GN-z11 is more extended towards the south-west (up in the MSA shutter in this view).  \n<!-- image -->  \nFig. 7. LymanGLYPH<11> velocity o GLYPH<11> set ( GLYPH<1> v Ly GLYPH<11> ) versus MUV for GN-z11 (star) and other high-redshift galaxies, color coded by LymanGLYPH<11> EW. We overplot data of z > 6 galaxies with ground-based observations from the literature (Cuby et al. 2003; Pentericci et al. 2011, 2016, 2018; Vanzella et al. 2011; Willott et al. 2013, 2015; Maiolino et al. 2015; Oesch et al. 2015; Stark et al. 2015, 2017; Furusawa et al. 2016; Knudsen et al. 2016; Carniani et al. 2017; Laporte et al. 2017; Mainali et al. 2017; Hashimoto et al. 2019; see Endsley et al. 2022 and the Table 4 therein) in circles, and Ly GLYPH<11> emitting galaxies at z GLYPH<24> 7 GLYPH<0> 9 from CEERS NIRSpec observations (Tang et al. 2023) in squares. Prediction of the correlation between Ly GLYPH<11> velocity o GLYPH<11> set and MUV at z = 7 from Mason et al. (2018b) is shown by the grey dashed line. GN-z11 has properties similar to the Ly GLYPH<11> emitting galaxies at z GLYPH<24> 7 GLYPH<0> 9.  \n<!-- image -->  \nline flux of LymanGLYPH<11> is about twice that of HGLYPH<13> (the strongest Balmer line we detect). From Case B recombination and assuming no dust as found from the Balmer line ratio, LymanGLYPH<11> would have about 50 GLYPH<2> the line flux of HGLYPH<13> , so it appears to be suppressed by about a factor of 26 GLYPH<2> (i.e., f esc,Ly GLYPH<11> = 0 : 038 GLYPH<6> 0 : 004), presumably through resonant scattering e GLYPH<11> ects.  \nThe discovery of LymanGLYPH<11> emission at such high redshift is remarkable, given the expected highly neutral IGM at this epoch so much earlier than the end of reionization at z GLYPH<25> 6 (Fan et al. 2001). However, perhaps this result is not so surprising when one considers the high rate of LymanGLYPH<11> detection in luminous 7 : 5 < z < 9 galaxies (Zitrin et al. 2015; Oesch et al. 2015; Stark et al. 2017; Larson et al. 2022; Finkelstein et al. 2013; Roberts-Borsani et al. 2016; Jung et al. 2019; Song et al. 2016) at redshifts prior to complete reionization. GN-z11 is a similarly luminous galaxy with M UV = GLYPH<0> 21 : 5 so the e GLYPH<11> ects that make LymanGLYPH<11> detectable in such galaxies (see Mason et al. 2018a) may be at play for GN-z11.  \nThere are two aspects of our LymanGLYPH<11> observations that may explain the significant transmission of f esc,Ly GLYPH<11> = 0 : 04. Firstly, the large velocity o GLYPH<11> set of 555 GLYPH<6> 32 km s GLYPH<0> 1 and rest-frame equivalent width are similar to those measured in luminous 7 : 5 < z < 9 galaxies with LymanGLYPH<11> (Figure 7; see also Tang et al. 2023). Large velocity o GLYPH<11> sets are key to the escape of LymanGLYPH<11> photons from galaxies in a highly-neutral IGM. Since the damping wing of the IGM and proximate HI will absorb photons close to the resonant frequency, photons that escape must resonantly scatter in the wings. Those that scatter far enough to the red may then be able to escape the system without being absorbed (Dijkstra 2014). We note that the infall motion of the neutral gas around galaxies may also play a role (Santos 2004; Sadoun et al. 2017; Weinberger et al. 2019; Park et al. 2021; Smith et al. 2022). If the peculiar velocity of neutral gas near a Lyman-a source is infalling, then even photons redward of the LymanGLYPH<11> will be resonantly absorbed, necessitating large velocity o GLYPH<11> sets of LymanGLYPH<11> to facilitate its escape.  \nAdditionally, the intense star formation in luminous galaxies will be driving powerful and fast-moving outflows. Outflows on the far side of the galaxy may provide a redshifted medium from which the photons can backscatter to our line-of-sight with the required velocity o GLYPH<11> set. In this context, our observation of spatially-extended LymanGLYPH<11> emission to the south-west suggests that if an outflow is present, it would extend in the north-east direction.', '3.4. Rest-frame UV properties of GN-z11': "From our low-dispersion prism spectra, where we have high S / N detection of the continuum, we measure a UV spectral slope of GLYPH<12> = GLYPH<0> 2 : 36 GLYPH<6> 0 : 10 (over the range GLYPH<21> rest = 1500 GLYPH<0> 2600 Å), consistent with that of GLYPH<12> = GLYPH<0> 2 : 4 reported from our NIRCam imaging in Tacchella et al. (2023). We measure a luminosity of M UV AB = GLYPH<0> 21 : 50 GLYPH<6> 0 : 02 over the range GLYPH<21> rest = 1400 GLYPH<0> 1600 Å (adopting a luminosity distance of 113,148.8 Mpc from our chosen cosmology). This corresponds to a luminosity density of L UV = 1 : 7 GLYPH<2> 10 29 erg s GLYPH<0> 1 cm GLYPH<0> 2 Hz GLYPH<0> 1 around GLYPH<21> rest = 1500 Å.  \nGLYPH<23>  \nThe rest-UV will be potentially a GLYPH<11> ected by dust reddening. However, from the prism spectrum, we measure a Balmer line ratio using H GLYPH<14> / H GLYPH<13> of 0 : 53 GLYPH<6> 0 : 06, which is very close and within the errors of the intrinsic ratio of 0 : 55 expected in an H ii region with electron density ne = 300 cm GLYPH<0> 3 and temperature Te = 15 ; 000 K, conditions expected in very high redshift galaxies (e.g. Curti et al. 2023; Katz et al. 2023; Isobe et al. 2023). We note that the wavelength baseline between H GLYPH<14> and H GLYPH<13> is short, so does not provide a large lever arm to quantify the dust attenuation accurately, and also that the H GLYPH<14> / H GLYPH<13> ratio of the fluxes from our 3-pixel medium grating spectrum is 0 : 68 GLYPH<6> 0 : 20, above the case B value of 0 : 55 but consistent within the errors. Our full-SED beagle fits to the prism spectrum, assuming that  \nthis is a star-forming galaxy rather than an AGN, also suggest low attenuation ( AV GLYPH<25> 0 : 17, only 70% of which is from dust outside H ii regions a GLYPH<11> ecting nebular emission). Therefore, from the observed Balmer decrement and SED fitting we do not measure any considerable dust attenuation or reddening in the spectrum of GN-z11.  \nWe now turn to the production and potential escape of ionizing photons in GN-z11. We can potentially constrain the escape fraction of ionizing photons ( f esc) by looking at how many produce local recombinations (as tracked by the hydrogen Balmer emission lines), compared with the total number produced. Zackrisson et al. (2017) provide tracks of the rest-UV spectral slope ( GLYPH<12> , which is related to the hardness of the spectrum and hence the production of ionizing photons) and the equivalent width of H GLYPH<12> . Although we do not measure H GLYPH<12> in GN-z11, as it is beyond our spectral range, we can use the continuum slope we measure ( GLYPH<12> GLYPH<25> GLYPH<0> 2 : 4) along with the flux in H GLYPH<13> and the case B ratio (appropriate if f esc is low) of H GLYPH<13> / H GLYPH<12> = 0.468 to estimate log(EW(H GLYPH<12> ) = Å) = 1 : 8. From the plots of Zackrisson et al. (2017), this high H GLYPH<12> equivalent width suggests a low escape fraction of f esc . 0 : 1. Our beagle SED fits also yield a low f esc = 0 : 03 + 0 : 05 GLYPH<0> 0 : 02 . We do not see strong evidence for a 'reverse Balmer break' in our NIRSpec spectra, which might be expected from nebular continuum if the escape fraction is indeed low, although in the best-fit beagle SED the reverse Balmer break is small. Conversely, we also see no evidence for a Balmer break that would be indicative of a moderately evolved stellar population. This is consistent with the very young age determined by the beagle SED fitting ( t GLYPH<24> 19 Myr), with the light in the rest-frame UV and blue wavelengths we probe being completely dominated by a young stellar population.  \nAdditional constraints on f esc could potentially be derived from the presence of Mg ii GLYPH<21>GLYPH<21> 2795 ; 2802 emission in the prism spectrum (e.g. Chisholm et al. 2020). The considerable restframe EW of 12 Å for Mg ii might suggest the presence of ionized channels in the galaxy, potentially facilitating the escape of ionizing radiation and LymanGLYPH<11> . Similar to LymanGLYPH<11> , the resonant nature of Mg ii routinely causes strong absorption by low-ionization gas, while pure Mg ii emission is thought to indicate a porous ISM (Feltre et al. 2018; Henry et al. 2018; Witstok et al. 2021). Following the predicted relationship in Witstok et al. (2021) between the strength of Mg ii and the [Ne iii ] and [O ii ] lines, we estimate an intrinsic Mg ii GLYPH<21> 2795 flux of 3 : 1 GLYPH<2> 10 GLYPH<0> 19 erg s GLYPH<0> 1 cm GLYPH<0> 2 . This results in a Mg ii escape fraction of f esc, Mg ii GLYPH<24> 60% under the assumption of a typical doublet ratio of F 2795 = F 2802 GLYPH<25> 1 : 7 (which itself depends on f esc, Mg ii and the dust content; Chisholm et al. 2020). This is much larger than the estimated LymanGLYPH<11> escape fraction, and also larger than the f esc inferred above from the equivalent width of the Balmer lines and the BEAGLE SED fitting. However, it has been suggested that Mg ii escape could be more sensitive to dust rather than f esc particularly for galaxies in the optically thick regime, which may explain the discrepancy between the escape fractions measured from Balmer emission and Mg ii (e.g. Katz et al. 2022).  \nWe now consider the production of ionizing photons, under the assumption of a low escape fraction fesc as discussed above, and compare these with the non-ionizing UV continuum detected. In case B, f ( H GLYPH<11> ) = f ( H GLYPH<13> ) = 6 : 11, and 45% of recombinations result in an H GLYPH<11> photon being emitted (Osterbrock & Ferland 2006). We take the observed H GLYPH<13> line flux to be 1 : 2 GLYPH<2> 10 GLYPH<0> 18 erg s GLYPH<0> 1 cm GLYPH<0> 2 from the 5-pixel extraction of the prism spectrum (since the agreement of the flux calibration with the NIRCam imaging is better than for the grating, Appendix C). We  \nmake the assumption of no dust attenuation to obtain a hydrogen ionizing photon production rate of N ion = 8 : 8 GLYPH<2> 10 54 photons s GLYPH<0> 1 . This gives an ionizing photon production e GLYPH<14> ciency of GLYPH<24> ion = N ion = L UV GLYPH<23> = 5 : 2 GLYPH<2> 10 25 erg GLYPH<0> 1 Hz. This value log GLYPH<24> ion = 25 : 7 agrees with that from the beagle SED fitting log GLYPH<24> ion = 25 : 67 GLYPH<6> 0 : 02, and has higher ionizing e GLYPH<14> ciency than galaxies at much lower redshift (e.g., Chevallard et al. 2018 find log GLYPH<24> ion = 25 : 2 GLYPH<0> 25 : 8 in extreme galaxies at z GLYPH<24> 0, whereas Bouwens et al. 2016 find log GLYPH<24> ion = 25 : 3 in subL GLYPH<3> galaxies at z = 4 GLYPH<0> 5) but is comparable with that seen in z GLYPH<24> 7 GLYPH<0> 8 galaxies (e.g., Tang et al. 2023 who find log GLYPH<24> ion = 25 : 7 GLYPH<0> 26 : 0).  \nAlthough we have not ruled out an AGN component of GN-z11, we can place upper limits on the star formation rate based on the assumption that the observed line emission is powered solely by star formation. From the rate of ionizing photons, we can estimate the star formation rate subject to assumptions about the star formation history and initial mass function (IMF) of stars. Using the Kennicutt (1998) relation, SFR = 1 : 08 GLYPH<2> 10 GLYPH<0> 53 ( N ion = s GLYPH<0> 1 ) M GLYPH<12> yr GLYPH<0> 1 assuming a Salpeter (1955) IMF, gives a star formation rate of 90 M GLYPH<12> yr GLYPH<0> 1 . For a Chabrier (2003) IMF the star formation rate is 54 M GLYPH<12> yr GLYPH<0> 1 from the Kennicutt (1998) relation. Using the more recent H GLYPH<11> -based relation from Reddy et al. (2018), which is more representative of the conditions found in galaxies at high redshifts, we obtain a star formation rate of 35 M GLYPH<12> yr GLYPH<0> 1 again assuming Chabrier (2003) IMF with an upper mass cut-o GLYPH<11> of 100 M GLYPH<12> . Out beagle fit has a star formation rate of GLYPH<24> 19 M GLYPH<12> yr GLYPH<0> 1 for a Chabrier IMF with a higher upper-mass cut-o GLYPH<11> of 300 M GLYPH<12> . Using an upper-mass cut-o GLYPH<11> of 100 M GLYPH<12> reduces the number of ionizing photons per unit SFR to 62%, bringing the star formation rate to 31 M GLYPH<12> yr GLYPH<0> 1 , in agreement with the SFR derived using the Reddy et al. (2018) conversion.  \nWe can also potentially use the rest-frame UV continuum to infer the star formation rate (or an upper limit on this, if there is an AGN contribution to the rest-frame UV). Kennicutt (1998) give a relation SFR = 1 : 4 GLYPH<2> 10 28 GLYPH<2> ( L UV GLYPH<23> = erg s GLYPH<0> 1 Hz GLYPH<0> 1 ) M GLYPH<12> yr GLYPH<0> 1 for a Salpeter IMF, which would translate to a star formation rate of 24 M GLYPH<12> yr GLYPH<0> 1 for GN-z11. However, this relation is probably inappropriate since it assumes constant star formation for 100 Myr, and GN-z11 is likely much younger, so the UV luminosity will still be increasing even if star formation is constant, causing the star formation rate to be underestimated.", '3.5. ISM ionization and enrichment': "In this section we use line ratio diagnostics to explore the ionization state and metal enrichment of the ISM, again under the assumption that the emission line fluxes are not dominated by an AGN contribution. We detect a number of collisionally-excited metal lines, both of low ionization ([O ii ]) and high ionization (including N iii ], [Ne iii ], C iii ]), as well as Balmer lines from hydrogen recombination. Our wavelength coverage does not extend to the widely-used [O iii ] GLYPH<21> 5007, however we do have a robust detection of [Ne iii ] GLYPH<21> 3869 which has a similar ionization potential. Hence, we consider the line flux ratio [Ne iii ] GLYPH<21> 3869 / [O ii ] GLYPH<21>GLYPH<21> 3726, 3729 as a probe of ionization parameter ( U ) - [Ne iii ] / [O ii ] has been shown to track [O iii ] / [O ii ] well (e.g. Levesque & Richardson 2014; Witstok et al. 2021), which is the most widely-used indicator of U . We measure [Ne iii ] / [O ii ] = 1 : 12 GLYPH<6> 0 : 13 from the 3-pixel grating extraction ([Ne iii ] GLYPH<21> 3869 is blended in the prism), which is comparable to the redshift z GLYPH<24> 5 : 5 GLYPH<0> 9 : 5 NIRSpec sample presented in Cameron et al. (2023) from our JADES survey, and also z & 7 galaxies observed in the CEERS survey (Tang et al. 2023). Following the calibration set  \nTable 2. Estimates of GN-z11 physical parameters derived from beagle SED fitting of the prism spectrum of Figure 2  \n:  \nbeagle SED fitting of the prism spectrum with the uncertainties giving the extent of the 1 GLYPH<27> credible regions: stellar mass ( M , accounting for mass returned to the ISM through stellar winds and supernova explosions), star formation rate ( ), maximum age of the stars ( t ), the mass-weighted age of stars ( t m ), nebular metallicity ( Z neb), ionization parameter (log U S), V -band dust attenuation (A V ), ionizing photon production e GLYPH<14> ciency ( GLYPH<24> ion) and escape fraction of H-ionizing photons ( f esc; see Appendix A for details).  \nout in Witstok et al. (2021), this corresponds to an ionization parameter of log U = GLYPH<0> 2 : 03 GLYPH<6> 0 : 04. We find a similar value of log U = GLYPH<0> 2 : 25 GLYPH<6> 0 : 97 from our beagle SED fitting.  \nWereport a marginal detection of the [O iii ] GLYPH<21> 4363 line in our prism spectrum (partially blended with H GLYPH<13> ; Figure 3), which has already been observed in a number of z > 7 galaxies (e.g. Curti et al. 2023; Katz et al. 2023). Although this line can in theory be used to derive a Te -based ('direct method') metallicity, the absence of [O iii ] GLYPH<21> 5007 from our data means we cannot measure the temperature with the standard approach. The O iii ] GLYPH<21>GLYPH<21> 1660,1666 / [O iii ] GLYPH<21> 4363 ratio can also be used as a temperature diagnostic, but the low significance of the [O iii ] GLYPH<21> 4363 coupled with the marginal detection of O iii ] GLYPH<21>GLYPH<21> 1660, 1666 in our grating spectrum means that any derived temperature would be highly uncertain. Thus, we instead consider using strongline ratios to constrain the metallicity of GN-z11. A widely-used metallicity indicator is R23 (the log of the ratio of [O ii ] + [O iii ] to H GLYPH<12> ), but since [O iii ] GLYPH<21> 5007 and H GLYPH<12> fall beyond our spectral coverage, we cannot measure this ratio. We instead consider an analogous ratio of ([Ne iii ] GLYPH<21> 3869 + [O ii ] GLYPH<21>GLYPH<21> 3727) / H GLYPH<14> . All three of these emission lines are well detected in our grating spectra, and conveniently lie at very similar wavelengths which minimizes any uncertainties arising due to wavelength-dependent attenuation. We measure a ratio of log 10 (([Ne iii ] + [O ii ]) = H GLYPH<14> ) = 0 : 50 GLYPH<6> 0 : 07 from the grating (3-pixel spectral extraction). Following the calibrations from Witstok et al. (2021) (which provides [O iii ] / [Ne iii ] GLYPH<25> 15 at the derived ionization parameter) and assuming H GLYPH<14>= H GLYPH<12> = 0 : 268, this would be equivalent to R 23 GLYPH<25> 0 : 85. These values place GN-z11 in fairly close alignment with the median values presented in the Cameron et al. (2023) sample; their stacked spectra at z GLYPH<24> 6 ( z GLYPH<24> 8) show R 23 = 0 : 88 (0 : 86) and log([Ne iii ] / [O ii ]) = 0 : 05 (0 : 04). According to the binned average relationships presented in Nakajima et al. (2022), this suggests a metallicity in the range 7 : 59 < 12 + log(O / H) < 7 : 76, which corresponds to 0 : 08 GLYPH<0> 0 : 12 Z GLYPH<12> assuming a solar abundance of 12 + log( O = H ) GLYPH<12> = 8 : 69. Our beagle SED fitting yields a consistent value of Z n eb = 0 : 12 GLYPH<6> 0 : 02 Z GLYPH<12> .  \nIn Figure 8 we compare our [Ne iii ] / [O ii ] and ([Ne iii ] + [O ii ]) / H GLYPH<14> measurements from GN-z11 (plotted separately from the prism and the grating data) with measurements from z > 5 : 5  \ngalaxies from Cameron et al. (2023), z GLYPH<24> 0 galaxies from SDSS MPA-JHU catalogs 1 (Aihara et al. 2011) and photoionization model grids from Gutkin et al. (2016). This line-ratio diagram is analogous to the widely used R23-O32 'ionization vs. excitation' diagram since, as described above, [Ne iii ] / [O ii ] traces ionization and ([Ne iii ] + [O ii ]) / H GLYPH<14> traces excitation of both the high- and low-ionization metal ions.  \nThe Gutkin et al. (2016) models in Figure 8 demonstrate the two-valued nature of ([Ne iii ] GLYPH<21> 3869 + [O ii ] GLYPH<21>GLYPH<21> 3727) / H GLYPH<14> with metallicity. Although the signal-to-noise ratio requirements significantly cut down the available SDSS sample, one can still see clear evidence of this two-valued relation. The z > 5 : 5 sample from Cameron et al. (2023) appears to follow an extrapolation of the low-metallicity (high-ionization) branch of this two-valued sequence. We see that GN-z11 (diamond symbol) lies in good agreement with the sequence formed by these z > 5 : 5 galaxies. It falls between the Gutkin et al. (2016) Z = Z GLYPH<12> = 0.07 and Z = Z GLYPH<12> = 0.15 model lines, suggesting 12 + l og ( O = H ) GLYPH<25> 7 : 7, and lies proximal to the model values with log U = GLYPH<0> 2 : 0, consistent with the empirical values derived above.  \nWe now consider where GN-z11 might fall on the massmetallicity relation (see Maiolino & Mannucci 2019 for a review). The stellar mass estimated from beagle of log( M GLYPH<3> = M GLYPH<12> ) = 8 : 73 + 0 : 06 GLYPH<0> 0 : 06 is consistent with that derived from our NIRCam photometry of log( M GLYPH<3> = M GLYPH<12> ) = 9 : 1 GLYPH<6> 0 : 3 0 : 4 presented in Tacchella et al. (2023), again assuming that the light is dominated by the stellar population rather than an AGN. Our observed spectrum shows no evidence of a Balmer Break, and if the continuum is purely stellar, is dominated by a young stellar population. It is possible a more stochastic star formation history would fit a higher stellar mass. Comparing our metallicity and mass estimates for GN-z11 with the average reported for 8 < z < 10 galaxies in Nakajima et al. (2023) we find GN-z11 is o GLYPH<11> set to somewhat lower metallicity, albeit within the uncertainty quoted there. We note that the sample presented in that paper is still small and our understanding of the metallicities of galaxies at z > 8 will no doubt continue to evolve significantly over the coming years. We also note that the uncertainties on our derived metallicity are large. In particular, we caution that the set of emission lines used to determine the metallicity presented here has not been robustly calibrated. The systematic uncertainties associated with this quoted metallicity are likely very high, so robust conclusions cannot be drawn from this about the evolution of the mass-metallicity relation. Further work is needed to robustly calibrate shorter-wavelength metallicity diagnostics suitable for the study of z > 10 galaxies with NIRSpec.  \nWhat is more puzzling is the strong N iii ] and N iv ] emission observed in the rest-frame UV, especially given the absence of a convincing detection of O iii ] GLYPH<21>GLYPH<21> 1660,1666 in our grating spectrum (although the blend with He ii is detected in the lowdispersion prism spectrum). The N iii ] GLYPH<21> 1748 emission line complex is not often seen in the spectra of star-forming galaxies, although it is detected in 2 of 44 galaxies in the low-redshift CLASSY survey (Mingozzi et al. 2022), including Mk996 (James et al. 2009). At intermediate redshifts, N iii ] GLYPH<21> 1748 has been observed in stacks of rest-UV galaxy spectra at z GLYPH<24> 3 (e.g. Saxena et al. 2022) and is weakly detected in SL2SJ021737051329, a lensed arc at z = 1 : 84 with low metallicity and high ionization (Berg et al. 2018). However, N iii ] GLYPH<21> 1748 is typically observed to be weaker than the nearby [O iii ] GLYPH<21> 1660, 1666 lines.  \nThis ratio of N iii ] GLYPH<21> 1748 / O iii ] GLYPH<21>GLYPH<21> 1660, 1666 can be used to place constraints on nebular N / O abundance ratios (Garnett  \nFig. 8. Line ratio diagram, showing ([Ne iii ] + [O ii ]) / H GLYPH<14> vs. [Ne iii ] / [O ii ], featuring GN-z11 - the yellow diamond denotes the line ratios derived from the medium-dispersion G395M grating, and the cyan diamond uses the low-dispersion prism spectrum (where we have corrected for the blending of [Ne iii ] GLYPH<21> 3869 with He i GLYPH<21> 3889 using the flux ratio from the grating). The background grey 2D PDF shows the subset of SDSS galaxies with 0 : 03 < z < 0 : 1 for which [Ne iii ] GLYPH<21> 3869, [O ii ] GLYPH<21>GLYPH<21> 3726, 3729 and H GLYPH<14> are all detected with S = N > 5. Purple squares show z > 5 : 5 galaxies from Cameron et al. (2023) after adjusting the reported ratios to be in terms of H GLYPH<14> by assuming a fixed value of H GLYPH<14>= H GLYPH<12> = 0 : 268. Solid lines show model grids from Gutkin et al. (2016), plotted for nine di GLYPH<11> erent values of metallicity ( Z = Z GLYPH<12> = 0.04, 0.07, 0.15, 0.30, 0.45, 0.60, 0.75, 1.0, 1.5) indicated by the di GLYPH<11> erent colours, and seven values of ionization parameter, indicated by marker sizes, in steps of 0 : 5 from log U = GLYPH<0> 4 : 0 (smallest) to log U = GLYPH<0> 1 : 0 (largest).  \n<!-- image -->  \net al. 1995). The conversion of N iii ] / O iii ] to N ++ / O ++ depends on the electron temperature- and density-sensitive emissivities of these emission lines. However, the temperature and density dependence of these emission lines are remarkably similar. Adopting N iii ] / O iii ] & 2 : 6 (see Table 1), any adopted values of temperature 1 GLYPH<20> Te = 10 4 K GLYPH<20> 55 and density 2 GLYPH<20> log( ne = cm GLYPH<0> 3 ) GLYPH<20> 10 results in emissivities that imply 0 : 72 GLYPH<20> N ++ = O ++ GLYPH<20> 1 : 09, significantly higher than the solar N / O value of 0.14 2  \nThe measured N ++ = O ++ may over-estimate the total N / O if there is a significant fraction of oxygen in other ionisation states. The second and third ionisation energies of nitrogen (29.6 and 47.4 eV) are milder than those of oxygen (35.1 and 54.9 eV). Assuming a simply multi-zone model of the ionisation structure of the ISM, this implies that N ++ = (O + + O ++ ) should be a lower limit on the total N / O. However, from detections of [O ii ] GLYPH<21>GLYPH<21> 3727 and [O iii ] GLYPH<21> 4363 emission for GN-z11, if we assume the [O ii ] emission arises from gas with density below the critical density of [O ii ] GLYPH<21>GLYPH<21> 3727 (i.e. ne . 10 4 K ), we get an approximate lower limit of O ++ = O + & 1 : 5, consistent with the expectation of a highly ionised ISM. Thus, even if we conservatively assume O ++ = O + = 1 : 5, this only lowers the inferred N / O by a factor of 0.6, implying a lower limit on the total nitrogen to oxygen abundance ratio of N / O > 0 : 43, or log 10(N = O) > GLYPH<0> 0 : 36, more than two times higher than the solar abundance ratio. This would appear quite unusual with respect to z GLYPH<24> 0 GLYPH<0> 2 galaxies (e.g. Pérez-Montero & Contini 2009; Hayden-Pawson et al.  \n2022), and strongly inconsistent with canonical chemical evolution models (see Maiolino & Mannucci 2019 or Kobayashi 2022 for reviews).  \nWe note that this simple calculation is independent of the excitation source (i.e. stellar photoionisation or AGN). However, we cannot rule out the scenario in which only a small fraction of the gas in GN-z11 is highly nitrogen enriched, but that this gas is extremely luminous in emission and dominates the global spectrum. More detailed modelling of the ionisation states of nitrogen and oxygen throughout the ISM of GN-z11 would be required to derive a more precise value of N / O, which is beyond the scope of this paper.  \nWe also detect the [C iii ] GLYPH<21> 1907 + C iii ] GLYPH<21> 1909 line in our G235M spectrum. The C iii ] line has been much more widely observed in star-forming galaxies at high redshift (e.g. Saxena et al. 2022; Arellano-Córdova et al. 2022; Jones et al. 2023), and its presence does not necessarily point to unusual C / Oabundance ratios (Arellano-Córdova et al. 2022; Jones et al. 2023).  \nIn summary, the emission line ratios measured for GN-z11 suggest a very high ionization parameter and low oxygen abundance in the vicinity of 10 % solar, broadly in line with findings from galaxies at z GLYPH<24> 6 GLYPH<0> 10 (Cameron et al. 2023; Sanders et al. 2023; Mascia et al. 2023; Nakajima et al. 2023; Tang et al. 2023). However, the detection of strong N iii ] emission suggests unexpected abundance patterns, which may have deeper implications for chemical enrichment histories.", '4. Conclusions': 'We present JWST / NIRSpec spectroscopy of one of the most luminous galaxies at z > 10. GN-z11 is in the GOODS-North field and had previously been identified as a Lyman break galaxy candidate by Oesch et al. (2015), with a tentative redshift of z = 11 : 1 from a continuum break in slitless HST / WFC3 spectroscopy (Oesch et al. 2016). We see numerous emission lines and a strong LymanGLYPH<11> break in our NIRSpec spectroscopy, and we unambiguously measure the redshift to be z = 10 : 603. Our grating spectrum reveals LymanGLYPH<11> in emission, making it the first object at z > 9 with confirmed LymanGLYPH<11> emission. The rest-frame equivalent width is W 0 = 18 Å. The emission is o GLYPH<11> -set 555 km s GLYPH<0> 1 redward of the systemic redshift and spatially extended. These properties are consistent with models of LymanGLYPH<11> backscattering o GLYPH<11> the far side of galactic scale outflows.  \nThe NIRSpec spectrum of GN-z11 is remarkably rich with emission lines, enabling us to study the ISM properties at z > 10. Based on the high [Ne iii ] / [O ii ] ratio we infer a high ionization parameter (log( U ) > GLYPH<0> 2 : 0). We report a significant detection of the very rarely-seen N iii ] GLYPH<21> 1748 line, which could suggest unusually high N / O ratios. While some high ionization lines are detected, the He ii GLYPH<21> 1640 and C iv GLYPH<21> 1550 lines, which are typically associated with photoionization due to AGN, are weak. Although we cannot conclusively rule our the contribution of an AGN, if this galaxy is indeed powered by star formation then the Balmer emission lines and UV continuum suggest a current star formation rate of GLYPH<24> 30 M GLYPH<12> yr GLYPH<0> 1 and low dust attenuation.  \nWe have presented a very high signal-to-noise spectrum of a galaxy at z > 10, showing continuum and line emission, highlighting the power of our JADES observations to not only measure redshifts but to do detailed studies of the physical and chemical properties of galaxies formed within the first few hundred million years of the Big Bang.  \nAcknowledgements. AJB, AS, AJC, GCJ, JC, and IEBW acknowledge funding from the "FirstGalaxies" Advanced Grant from the European Research  \nCouncil (ERC) under the European Union\'s Horizon 2020 research and innovation programme (Grant agreement No. 789056). ECL acknowledges support of an STFC Webb Fellowship (ST / W001438 / 1). The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant no.140. RS acknowledges support from a STFC Ernest Rutherford Fellowship (ST / S004831 / 1). RM, JW, MC, FDE, JS, TJL, LS, and WMB acknowledge support by the Science and Technology Facilities Council (STFC) and by the ERC through Advanced Grant 695671 "QUENCH". RM also acknowledges funding from a research professorship from the Royal Society. JW also acknowledges funding from the Fondation MERAC. This research is supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. FS, EE, DJE, BDJ, MR, BER, IS, and CNAW acknowledge a JWST / NIRCam contract to the University of Arizona NAS5-02015. DJE is also supported as a Simons Investigator. SC acknowledges support by European Union\'s HE ERC Starting Grant No. 101040227 - WINGS. SA, BRDP, and MP acknowledges support from the research project PID2021-127718NB-I00 of the Spanish Ministry of Science and Innovation / State Agency of Research (MICIN / AEI). HÜ gratefully acknowledges support by the Isaac Newton Trust and by the Kavli Foundation through a Newton-Kavli Junior Fellowship. Funding for this research was provided by the Johns Hopkins University, Institute for Data Intensive Engineering and Science (IDIES). RB acknowledges support from an STFC Ernest Rutherford Fellowship [grant number ST / T003596 / 1]. MP also acknowledges support from the Programa Atracción de Talento de la Comunidad de Madrid via grant 2018-T2 / TIC11715. LW acknowledges support from the National Science Foundation Graduate Research Fellowship under Grant No. DGE-2137419. DP acknowledges support by the Huo Family Foundation through a P.C. Ho PhD Studentship. This work is based [in part] on observations made with the NASA / ESA / CSA James Webb Space Telescope. 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We fit varying all stellar and nebular parameters (metallicity, ionization parameter, dust-to-gas mass ratio), employ a delayed exponential star formation history with recent 10 Myr of constant star formation that can vary independently. Finally, we model attenuation by dust using the Charlot & Fall (2000) two-component dust law. We also allow for a damping wing for the neutral intergalactic medium following the prescription described in Curtis-Lake et al. (2023), though we do not report the values here as they will be a GLYPH<11> ected by the Ly GLYPH<11> flux which is unresolved in the PRISM spectrum. The resulting spectral fit and derived parameters are shown in Fig. A.1 and reported in Table 2. The Gutkin et al. (2016) nebular models employ a relation between N / O and O / H abundances, which gives low N / O abundance at low metallicity. As such, our fit does not reproduce the rest-frame UV Nitrogen lines. We therefore mask them to prevent their presence a GLYPH<11> ecting the fit to the rest-frame UV continuum. We also mask the region around C iv , which shows an o GLYPH<11> set in the emission from the expected wavelength.', 'Appendix B: R GLYPH<24> 1000 grating 1D and 2D spectra': 'Figure B.1 shows the full NIRSpec medium-resolution grating spectra with detected emission lines marked.', 'Appendix C: Comparison of NIRSpec flux calibration to NIRCam imaging': "As a check on our spectroscopic flux calibration, we compare the GNz-11 fluxes derived from the NIRSpec spectroscopy with the NIRCam fluxes across several filters reported in Tacchella et al. (2023). Given the small spatial size of the source, and the narrow (0 00 : 2-wide) NIRSpec microshutters, we use the 0 00 : 2-diameter NIRCam aperture photometry (corrected to total magnitudes assuming a point source) reported in Tacchella et al. (2023) and our 3-pixel (0 00 : 3-wide) NIRSpec spectral extraction (again corrected for slit losses to approximate total flux assuming a point source at the location of GN-z11 with the microshutter). Each extracted spectrum was converted to photons per unit wavelength (since NIRCam detects photons, not energy), and the flux density integrated over the bandpass of each filter, weighting by the filter transmission curve. We then computed the brightness (in nJy) of a source with a spectrum uniform in f GLYPH<23> (i.e. flat in AB magnitudes) which would produce the same integrated flux, so as to compare with the quoted fluxes for NIRCam on the AB system (see Table C.1).  \nAs can be seen from Figure C.1, the agreement in flux between the low-dispersion prism spectrum and the NIRCam photometry is excellent, with most filters agreeing with the spectral fluxes within the nominal error bars (the agreement is generally within 5%). The flux calibration of the grating spectra is less accurate. The grating spectra show significantly higher fluxes than NIRCam (or the prism spectrum) at 2 : 5 < GLYPH<21> < 4 GLYPH<22> m at the GLYPH<25> 15 GLYPH<0> 20% level, greater than the nominal uncertainties in the photon statistics, although at other wavelengths the agreement is  \nTable C.1. Comparison of the NIRCam photometry of GN-z11 with the NIRSpec spectroscopy.  \nThe NIRCam photometry of GN-z11 in a 0 00 : 2-diameter aperture (column 2) from Tacchella et al. (2023) is compared with that inferred from the spectroscopy in the low-dispersion prism (column 3) and medium-dispersion gratings (flux in column 4, and grating which overlaps that filter in column 5). The spectroscopic measurements use the 3-pixel extraction.  \nbetter. The exact origin of this is unclear, but the flux calibration of the gratings may be less good, or there may be background subtraction issues a GLYPH<11> ecting the measured flux.  \nFig. A.1. Triangle plot showing the 2D (1D on diagonal) posterior probability distributions for the derived stellar mass ( M , accounting for mass returned to the ISM through stellar winds and supernova explosions), star formation rate ( ), maximum age of the stars ( t ), e GLYPH<11> ective V -band attenuation optical depth ( ˆ GLYPH<28> v = AV = 1 : 086), ionization parameter (log U S), nebular metallicity ( Z neb), escape fraction of H-ionizing photons ( f esc) and ionizing photon production e GLYPH<14> ciency ( GLYPH<24> ion). The contours in the 2D posterior plots show the 1, 2 and 3 GLYPH<27> credible regions in light, medium and dark blue, respectively. The inset shows the resulting fit to the prism spectrum, with the spectrum and 1 GLYPH<27> standard errors shown as red line and shaded region respectively, and 1 GLYPH<27> range of fitted model spectra in blue. Regions that are masked in the spectrum are shown as fainter red (data) and fainter blue (model) shaded regions.  \n<!-- image -->  \nbrew install ilmbase  \nFig. B.1. Full coverage of the 2D and 1D spectra from the medium resolution G140M (top), G235M (middle) and G395M (bottom) gratings. The main emission lines observed in the spectra have been marked.  \n<!-- image -->  \nFig. C.1. The NIRSpec low-dispersion prism spectrum of GN-z11 (3-pixel extraction), compared with the NIRCam photometry in di GLYPH<11> erent filters (red error bars, denoting the flux uncertainty and the wavelength span of the filter bandpass). The large diamond symbols denote the flux from the NIRSpec spectrum integrated over the filter response curve, with the small blue error bars within these diamond symbols.  \n<!-- image -->  \nFig. C.2. The NIRSpec medium-dispersion grating spectrum of GN-z11 (3-pixel extraction, smoothed in the spectral direction with a 11-pixel boxcar), compared with the NIRCam photometry in di GLYPH<11> erent filters (red error bars, denoting the flux uncertainty and the wavelength span of the filter bandpass). The light grey spectrum is the G235M, with the G140M and G395M grating spectra in black. The ' + ' symbols and blue error bars denote the flux from the NIRSpec spectrum integrated over the filer response curve.  \n<!-- image -->"}