We present JWSTNIRSpec prism spectroscopy of MACS0647JD a triply lensed z  11 candidate discovered in Hubble Space Telescope imaging and spatially resolved by JWST imaging into two components A and B. Spectroscopy of component A yields a spectroscopic redshift z  10.17 based on seven detected emission lines C III  1907 1909 O II 3727 Ne III 3869 Ne III 3968 H 4101 H 4340 and O III 4363. These are the secondmost distant detections of these emission lines to date in a galaxy observed just 460 million years after the Big Bang. Based on observed and extrapolated line flux ratios we derive a gasphase metallicity 12  logOH  7.58.0 or Z  0.060.2 Z SUBSUB ionization parameter inlineformula mmlmath overflowscrollmmlmilogmmlmimmlmo stretchyfalsemmlmommlmiUmmlmimmlmo stretchyfalsemmlmommlmath inlineformula  1.9  0.2 and an ionizing photon production efficiency inlineformula mmlmath overflowscrollmmlmilogmmlmimmlmo stretchyfalsemmlmommlmsubmmlmrowmmlmimmlmimmlmrowmmlmrowmmlmiionmmlmimmlmrowmmlmsubmmlmo stretchyfalsemmlmommlmommlmommlmn25.2mmlmnmmlmommlmommlmn0.2mmlmnmmlmspace width0.25emmmlmspacemmlmath inlineformula ergSUP1SUP Hz. The spectrum has a softened Ly break evidence for a strong Ly damping wing. The Ly damping wing also suppresses the F150W photometry explaining the slightly overestimated photometric redshift z  10.6  0.3. MACS0647JD has a stellar mass logMM SUBSUB  8.1  0.3 including 6  10SUP7SUP M SUBSUB in component A most of which formed recently within 20 Myr with a star formation rate  2  1 M SUBSUB yrSUP1SUP all within an effective radius 70  24 pc. Spectroscopy of a fainter companion galaxy C separated by a distance of  3 kpc reveals a Lyman break consistent with z  10.17. MACS0647JD is likely the most distant galaxy merger known.
['Galaxies', 'High-redshift galaxies', 'Early universe', 'Strong gravitational lensing', 'Galaxy spectroscopy', 'Reionization', '573', '734', '435', '1643', '2171', '1383', 'Astrophysics - Astrophysics of Galaxies', 'Astrophysics - Cosmology and Nongalactic Astrophysics']
JWST NIRSpec Spectroscopy of the Triply Lensed z  10.17 Galaxy MACS0647JD
{'JWST NIRSpec spectroscopy of the triply-lensed z = 10 . 17 galaxy MACS0647-JD': "Tiger Yu-Yang Hsiao , 1, 2, 3, ∗ Abdurro'uf , 2, 3, ∗ Dan Coe , 3, 4, 2 Rebecca L. Larson , 5 Intae Jung , 3 Matilde Mingozzi , 3 Pratika Dayal , 6 Nimisha Kumari , 3, 4 Vasily Kokorev , 7 Anton Vikaeus , 8 Gabriel Brammer , 9, 10 Lukas J. Furtak , 11 Angela Adamo , 12 Felipe Andrade-Santos , 13, 1, 14 Jacqueline Antwi-Danso , 15, 16 Maruˇsa Bradaˇc , 17, 18 Larry D. Bradley , 3 Tom Broadhurst , 19, 20, 21 Adam C. Carnall , 22 Christopher J. Conselice , 23 Jose M. Diego , 24 Megan Donahue , 25 Jan J. Eldridge , 26 Seiji Fujimoto , 7, † Alaina Henry , 3, 2 Svea Hernandez , 4, 3 Taylor A. Hutchison , 27, ‡ Bethan L. James , 3, 4 Colin Norman , 2, 3 Hyunbae Park , 28 Norbert Pirzkal , 3 Marc Postman , 3 Massimo Ricotti , 29 Jane R. Rigby , 27 Eros Vanzella , 30 Brian Welch , 27, 29 Stephen M. Wilkins , 31, 32 Rogier A. Windhorst , 33 Xinfeng Xu , 34, 35 Erik Zackrisson , 8 and Adi Zitrin 11  \n1 Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA 2 Center for Astrophysical Sciences, Department of Physics and Astronomy, The Johns Hopkins University, 3400 N Charles St. Baltimore, MD 21218, USA  \n3 Space Telescope Science Institute (STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA  \n- 4 Association of Universities for Research in Astronomy (AURA), Inc. for the European Space Agency (ESA)  \nSchool of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA  \n6  \nKapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700AV Groningen, The Netherlands  \n7  \nThe University of Texas at Austin, Department of Astronomy, Austin, TX, United States  \n- 8 Observational Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden 9 Cosmic Dawn Center (DAWN), Copenhagen, Denmark  \n10  \nNiels Bohr Institute, University of Copenhagen, Jagtvej 128, Copenhagen, Denmark  \n- 11 Physics Department, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel  \nDepartment of Astronomy, Oskar Klein Centre, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm, Sweden  \n13  \nDepartment of Liberal Arts and Sciences, Berklee College of Music, 7 Haviland Street, Boston, MA 02215, USA  \n14  \nClay Center Observatory, Dexter Southfield, 20 Newton Street, Brookline, MA 02445, USA  \n15 George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 78743, USA  \n- 16 Department of Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, TX 78743, USA  \n17  \nDepartment of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, SI-1000 Ljubljana, Slovenia  \n18  \nDepartment of Physics and Astronomy, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA  \n- 19 Department of Theoretical Physics, University of the Basque Country UPV-EHU, E-48040 Bilbao, Spain\n- 20 Donostia International Physics Center (DIPC), 20018 Donostia, The Basque Country, Spain\n- 21 IKERBASQUE, Basque Foundation for Science, Alameda Urquijo, 36-5 E-48008 Bilbao, Spain  \n22  \nInstitute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK  \nJodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK  \n24  \nInstituto de F'ısica de Cantabria (CSIC-UC). Avda. Los Castros s/n. 39005 Santander, Spain  \n25  \nMichigan State University, Physics & Astronomy Department, East Lansing, MI, USA  \n- 26 Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand\n- 27 Observational Cosmology Lab, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 28 Lawrence Berkeley National Laboratory, CA 94720, USA  \n29 Department of Astronomy, University of Maryland, College Park, 20742, USA  \nINAF - OAS, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, I-40129 Bologna, Italy  \n31  \nAstronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK  \n- 32 Institute of Space Sciences and Astronomy, University of Malta, Msida MSD 2080, Malta  \nSchool of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-6004, USA  \n33  \nDepartment of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA  \n30  \n34  \nCenter for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Avenue,  \nEvanston, IL, 60201, USA.  \nCorresponding author: Tiger Hsiao and Abdurro'uf  \ntiger.hsiao@cfa.harvard.edu, fabdurr1@jhu.edu  \n12  \n35  \n5  \n23", 'ABSTRACT': 'We present JWST /NIRSpec prism spectroscopy of MACS0647 -JD, the triply-lensed z ∼ 11 candidate discovered in HST imaging and spatially resolved by JWST imaging into two components A and B. Spectroscopy of component A yields a spectroscopic redshift z = 10 . 17 based on 7 detected emission lines: C iii ] λλ 1907,1909, [O ii ] λ 3727, [Ne iii ] λ 3869, [Ne iii ] λ 3968, H δ λ 4101, H γ λ 4340, and [O iii ] λ 4363. These are the second-most distant detections of these emission lines to date, in a galaxy observed just 460 million years after the Big Bang. Based on observed and extrapolated line flux ratios we derive a gas-phase metallicity 12+log(O/H) ∼ 7.5 - 8.0, or Z ∼ (0.06 - 0.2) Z ⊙ , ionization parameter log( U ) = -1 . 9 ± 0 . 2, and an ionizing photon production efficiency log( ξ ion ) = 25 . 2 ± 0 . 2 erg -1 Hz. The spectrum has a softened Lymanα break, evidence for a strong Lymanα damping wing. The Lymanα damping wing also suppresses the F150W photometry, explaining the slightly overestimated photometric redshift z = 10 . 6 ± 0 . 3. MACS0647 -JD has a stellar mass log( M/M ⊙ ) = 8 . 1 ± 0 . 3, including ∼ 6 × 10 7 M ⊙ in component A, most of which formed recently (within ∼ 20 Myr) with a star formation rate SFR ∼ 2 ± 1 M ⊙ yr -1 , all within an effective radius 70 ± 24 pc. Spectroscopy of a fainter companion galaxy C separated by a distance of ∼ 3 kpc reveals a Lyman break consistent with z ∼ 10 . 17. MACS0647 -JD is likely the most distant galaxy merger known.  \nKeywords: Galaxies (573), High-redshift galaxies (734), Early universe (435), Strong gravitational lensing (1643), Galaxy spectroscopy (2171)', '1. INTRODUCTION': "Spectroscopy using the NIRSpec instrument (Jakobsen et al. 2022; Ferruit et al. 2022; Boker et al. 2023) onboard JWST (Gardner et al. 2023; Rigby et al. 2023) is beginning to confirm distant galaxy candidates and reveal their properties in the early universe ( z > 8; e.g., Fujimoto et al. 2023; Roberts-Borsani et al. 2023; Bunker et al. 2023; Arrabal Haro et al. 2023a; Harikane et al. 2024; Curtis-Lake et al. 2023). With coverage out to 5 . 3 µ m, NIRSpec can detect the strong emission lines [O iii ] λ 4959, λ 5007 and H β in galaxies as distant as z ∼ 9 . 5, confirming redshifts and constraining properties such as metallicity and ionization parameter when combined with other emission lines (e.g., Williams et al. 2023; Nakajima et al. 2023; Boyett et al. 2024; Cameron et al. 2023b; Tang et al. 2023; Sanders et al. 2024; Jung et al. 2024).  \nAt z > 10, within the first 500 million years, spectroscopic confirmations and detailed studies are more challenging because [O iii ]+H β is redshifted out of the NIRSpec wavelength range, and fainter emission lines are difficult to detect in low-luminosity z > 10 galaxies. Brighter galaxies or longer exposure times are required. Curtis-Lake et al. (2023) presented deep spectra with a  \nspectral resolution of R ∼ 100 that impressively confirmed galaxies with redshifts z = 10 . 4, 11.6, 12.6, and 13.2 based on significant Lyman break detections and an absence of definitive emission lines in long exposures of 9 - 28 hours for these faint candidates (F200W AB mag 28 - 29). Similarly, Arrabal Haro et al. (2023a) confirmed galaxies at z = 10 . 1 and z = 11 . 4 based on Lyman break detections with no emission lines in 5-hour NIRSpec prism spectra that also revised the redshift of a z ∼ 16 candidate down to z = 4 . 912.  \nOver a decade of Hubble Space Telescope ( HST ) WFC3/IR observations yielded two z > 10 galaxies bright enough (F200W AB mag 25 . 8 ± 0 . 1) for more detailed study. GN-z11 was one of the most distant galaxies ever discovered in HST imaging (Oesch et al. 2016). They noted that given the search area, it was surprising to discover a galaxy so bright. JWST NIRCam (Rieke et al. 2023) imaging photometry yields F200W AB mag of 25 . 9 ± 0 . 1 and M UV = -21 . 6, or M UV = -21 . 8 corrected for dust (Tacchella et al. 2023). JWST NIRSpec spectroscopy has now confirmed GN-z11 at z = 10 . 603 and revealed 12 emission lines (Bunker et al. 2023).  \nMACS0647 -JD was the other similarly bright z ∼ 11 candidate discovered in HST imaging (Coe et al. 2013), supported by HST grism observations (Pirzkal et al. 2015), Spitzer imaging (Lam et al. 2019), and gravitational lens modeling (Chan et al. 2017). MACS0647-JD is triply-lensed by a massive foreground galaxy cluster, MACSJ0647.7+7015 ( z = 0 . 591; Ebeling et al. 2007).  \nDespite lensing magnifications of ∼ 8, 5, and 2 (Meena et al. 2023), the three lensed images JD1, JD2, and JD3 were spatially unresolved in HST imaging.  \nJWST /NIRCam imaging resolved MACS0647 -JD as having two small components in a possible galaxy merger at z = 10 . 6 ± 0 . 3 (Hsiao et al. 2023). The brighter component A has an effective radius r ∼ 70 ± 24 pc and appears bluer, ( β ∼ -2 . 6 ± 0 . 1), likely due to its young stellar population ( ∼ 50 Myr old) and no dust. The other component, JDB, has a smaller radius of r ∼ 20 +8 -5 pc and appears redder ( β ∼ -2 ± 0 . 2), , likely due to an older stellar population ( ∼ 100 Myr old) and mild dust ( A V ∼ 0 . 1 mag). The different inferred star formation histories suggest these two components formed separately and are in the process of merging. A third triplylensed component C was also identified 2 '' away ( ∼ 3 kpc in the delensed source plane). With similar colors and a consistent photometric redshift, C may be destined to merge with A and B.  \nCompared to GN-z11, MACS0647 -JD is intrinsically fainter ( M UV = -20 . 3), yet observed to be brighter; the brightest lensed image JD1 is F200W AB mag 25 . 0 ± 0 . 1. The brightest clump A is M UV = -19 . 5 and lensed to F200W AB mag of 25 . 8 ± 0 . 1 in JD1. This enables detailed study with JWST .  \nIn this paper, we report NIRSpec and NIRCam observations of MACS0647-JD obtained by JWST observation program GO 1433 (PI Coe). Most of the NIRCam images were analyzed previously by Hsiao et al. (2023). This work includes a new F480M image, deeper F200W data, and updated image reductions and photometry ( § 2). Based on NIRSpec prism ( R ∼ 100) spectroscopy spanning 0.7 - 5.3 µ m, we detect nebular emission lines, measure the spectroscopic redshift, and derive physical properties including the ionization parameter and metallicity using various emission line ratios as well as photometric spectral energy distribution (SED) fitting ( § 3). We present conclusions in § 4.", '2. OBSERVATIONS': 'JWST program GO 1433 (PI Coe) observed MACS0647 -JD as summarized in Table 1. We also analyze archival HST imaging from programs GO 9722, 10493, 10793, 12101, and 13317, described in Hsiao et al. (2023). All JWST and HST data are publicly available in the Mikulski Archive for Space Telescopes (MAST; DOI:10.17909/wpys-ap03). We also provide reduced data products 1 along with our data analysis scripts. 2', '2.1. NIRSpec MOS prism spectroscopy': "There were two separate NIRSpec multi-object spectroscopy (MOS) observations (Obs 21 and Obs 23) using the microshutter assembly (MSA). Both used the lowresolution R ∼ 30 -300 prism yielding data from 0.6 5.3 µ m. Obs 23 was performed with standard 3-slitlet nods used to subtract backgrounds measured near each target. The total exposure time was 1.8 hours. Obs 21 was performed with single slitlets, requiring backgrounds to be measured in nearby slitlets designed to observe 'blank' sky and intracluster light. Two MSA configurations were executed in Obs 21 with a total exposure time of 1.8 hours. The two configurations were similar with small dithers between them and most targets included in both.  \nThe two brightest lensed images of MACS0647 -JD (JD1 and JD2) were observed in all exposures of all observations for a total exposure time of 3.6 hours. The slitlets primarily captured light from the brightest clump A. The brightest lensed images of the companion galaxy C (JD1C and JD2C) were also observed in all exposures. Since JD1 and JD2 are multiple images of the same object with JD2 magnified ∼ 70% as bright ( µ ∼ 5 . 3) as JD1, the resulting summed spectra have signal-to-noise ratio (SNR) similar to 6-hour total effective exposure times on JD1A and JD1C.  \nClump B was observed only in Obs 21 of JD2. Given its proximity to clump A, it is difficult to spatially resolve its contribution to the JD2 spectrum. They are separated by only one or two 0.1 '' pixels in the cross-dispersion direction (i.e., in the 2D NIRSpec spectrum). We do perhaps detect some emission line fluxes (i.e.,C iii ] λλ 1907,1909) from JD2B as we discuss in § 3.4 (see also the second row of Figure 1).  \nWe retrieved NIRSpec Level 1 data products from MAST and processed them with the STScI JWST pipeline 3 version 1.9.2 and msaexp 4 version 0.6.0. First, msaexp corrects for 1/ f noise 5 , masks snowballs 6 , corrects bias levels in individual exposures, and rescales the noise array RNOISE based on measurements in blank regions. Next, we run JWST pipeline Stage 2 routines to perform WCS registration, flat-fielding, pathloss corrections, and flux calibration.  \nFor the 3-slitlet data, background subtraction is performed locally before drizzling the 3 exposures onto a  \ncommon 2D pixel grid. For the single-slitlet data, we drizzle-combined data from the 2 exposures (MSA configurations). Then we subtracted the 2D background spectrum in a nearby slit (#50981) that observed a relatively blank region of the image.  \nTo extract each 1D spectrum, msaexp uses a Gaussian profile in the cross-dispersion direction, derived from an inverse-weighted sum of the 2D spectrum in the dispersion direction, based on the optimal extraction described in Horne (1986). The results are shown in Figure 1 for each observation. The plots show the numbers for the extraction Gaussian: offset ± width in pixels. There are no design choices to exclude any contribution from clumps A and B.  \nFinally, we sum the 1D spectra, adding flux uncertainties in quadrature, yielding the spectrum shown in Figure 2. This spectrum includes the total flux observed in all 4 exposures for JD1A and JD2A.", '2.2. NIRCam imaging': "NIRCam imaging was obtained first in 6 filters, F115W, F150W, F200W, F277W, F365W, and F444W spanning 1-5 µ m, and the results were studied and presented in Hsiao et al. (2023). Additional NIRCam imaging has since been obtained in F200W and F480M, concurrent with the NIRSpec Obs 21. The F480M observation was included to observe MACS0647 -JD redward of the Balmer break to better constrain its stellar age and mass. Each NIRCam image has an exposure time of 35 minutes, split between 4 INTRAMODULEBOX dithers that cover the short-wavelength gaps.  \nWe process the NIRCam images using the STScI JWST pipeline and grizli (Brammer et al. 2022). In Hsiao et al. (2023), we analyzed the fourth release (v4) of the images reduced with grizli and then performed zeropoint corrections based on updated calibrations that remain robust today (Boyer et al. 2022). Those updated zeropoints were implemented in grizli v5. In this work, we analyze grizli v6 image mosaics 7 featuring improved sky flats, bad pixel tables, wisp templates, and longwavelength zeropoints.  \nBriefly, in each NIRCam exposure, the grizli pipeline applies corrections for 1 /f noise striping and masks 'snowballs' 8 and 'wisps' 9 . Then grizli drizzlecombines all exposures in each filter on to a common  \npixel grid using astrodrizzle (Koekemoer et al. 2003; Hoffmann et al. 2021). The NIRCam short wavelength images are drizzled to 0 . '' 02 pixels, and all other images are drizzled to 0 . '' 04 pixels. All images are aligned with coordinates registered to GAIA DR3 (Gaia Collaboration et al. 2021). We create color images using trilogy 10 (Coe et al. 2012).  \nWe measure JWST photometry of the lensed images JD1 and JD2 using grizli with circular apertures of 0 . '' 25 radius. The segmentation process and photometry measurements with grizli pipeline were done automatically to all detected galaxies in the field with circular apertures. We then measure the photometry of the JD components A and B individually using piXedfit (Abdurro'uf et al. 2023) within elliptical apertures as described in Hsiao et al. (2023) centered at the central pixel (brightest pixel in F444W) of each component. Both grizli and piXedfit described in Hsiao et al. (2023) v4 of the images while in this letter we anaylze v6 images as described earlier in this section. No significant change is found in the result from SED fittings. Additionally, we create rectangular photometric apertures that match the NIRSpec slitlets in size, position, and orientation in each of our 4 observations for JD1 and JD2 (see Figure 1) 11 . We find this photometry is very similar to the photometry of component A, because the NIRSpec slitlets primarily targeted A with occasional small contributions from the fainter clump B. All resulting NIRCam photometry is presented in Table 2 and plotted along with the NIRSpec spectrum in Figure 3.  \nWe note the photometry of clump A ( β ∼ -2 . 6 ± 0 . 1) is slightly redder than the observed spectrum ( β ∼ -2 . 8). Both measurements present challenges, including the proximity of the A and B clumps, and variable slit loss corrections as a function of wavelength applied by the JWST pipeline to the NIRSpec spectrum.", '3. RESULTS AND DISCUSSION': "We obtain four spectra of MACS0647 -JD component A in the lensed images JD1 and JD2 (Figure 1). Obs 21 of JD2 also includes flux from the fainter component B. We have not attempted to extract signal from  \nTable 1. JWST Observations of MACS0647  \nTable 2. NIRCam photometry of MACS0647 -JD  \nNote. All flux densities are given in nJy, and are not de-lensed. Photometry is plotted in Figure 3 along with the spectrum.  \nTable 3. Measured emission line fluxes for JDA  \nFigure 1. Individual NIRSpec spectra of MACS0647 -JD lensed images JD1 and JD2 (#3593 and #3349, respectively, in the catalog used to prepare NIRSpec Observations 21 and 23). Left : Slitlets in red are overlaid on 2 '' × 2 '' NIRCam color images (blue F115W; cyan F150W; green F200W; red F277W, F356W, F444W, F480M). Note that most of the observations target the brighter component A. Right : 2D spectra vs. rest-frame wavelength for z = 10 . 17 (top) and 1D spectra F ν ( µ Jy) vs. observed wavelength in microns (bottom). In each 1D plot, the gray line shows the spectrum, and the red line shows the uncertainty. Faint vertical colored shaded regions mark wavelengths of common emission lines: Ly αλ 1216 (pink), C iii ] λλ 1907,1909 (green), Mg ii λ 2800 (blue), [O ii ] λ 3727 (purple), [Ne iii ] λ 3869 (yellow), [Ne iii ] λ 3968 (red), H δ (orange), and H γ (gray). Only two of those (C iii ] and [O ii ]) appear in MACS0647 -JD, along with others revealed in the summed spectrum (Figure 2) and listed in Table 3.  \n<!-- image -->  \nFigure 2. Spectrum and photometry of MACS0647 -JD component A in the sum of both lensed images in both observations (i.e., JD1 Obs 21 + JD1 Obs 23 + JD2 Obs 21 + JD2 Obs 23), with a total magnification ∼ 26 . 6 = 8 + 8 + 5 . 3 + 5 . 3. The spectrum is the sum of all 4 observed spectra. The photometry shown here is measured within rectangular apertures resembling the NIRSpec slits in the 4 exposures. The red line is the piXedfit model fit to the spectrum with emission lines masked out. After subtracting this continuum (bottom panels), detected emission lines are fit with Gaussian functions (blue) to measure fluxes. (Other undetected emission lines are labeled in gray.) The best-fit model continuum is smoothed with a constant spectral resolution (R) of 100, which corresponds to velocity resolution of ∼ 3000 km/s. We also see a hint of CIV absorption, as we mention in the last paragraph of § 3.4. Note that at the wavelength of CIV, ∼ 1 -2 µ m, R falls to ∼ 30, which is lower than R in our fitting.  \n<!-- image -->  \ncomponent B that might be isolated from A in the crossdispersion direction.  \nThe summed spectrum of all four observations (JD1 Obs 21, JD1 Obs 23, JD2 Obs 21, and JD2 Obs 23) is shown in Figure 2, with a total magnification of 26 . 6 = 8 + 8 + 5 . 3 + 5 . 3. We detect the continuum between 1.5 and 5.3 µ m with SNR > 10 per spectral resolution element out to ∼ 3 µ m; flux decreases and noise increases to longer wavelengths. Rather than a sharp Lyman break, the spectrum rolls off gradually from 1.5 µ m(1343 ˚ A rest-frame) to the Lyman break observed  \nat 1.36 µ m(1216 ˚ Arest-frame). In § 3.7 we show that this attenuation is consistent with a Lymanα damping wing.  \nWe detect seven emission lines (including unresolved doublets): C iii ] λλ 1907,1909, [O ii ] λλ 3727,3729, [Ne iii ] λ 3869, [Ne iii ] λ 3968, H δ λ 4101, H γ λ 4340, and [O iii ] λ 4363, all with SNR > 4. We also marginally detect HeI λ 4473 with SNR ∼ 2.8. Based on the observed wavelengths of these lines, we measure a spectroscopic redshift z spec = 10 . 17. Harikane et al. (2024) recently reported the same redshift for MACS0647 -JD based on a fraction of the data: JD1 Obs 23.  \nFigure 3. MACS0647 -JD NIRSpec summed spectrum (divided by 4; gray) compared with photometry presented in Table 2. Black points show the photometry measured in rectangular apertures that mimic the observed NIRSpec slits. These synthetic colors match the JD1A and JD2A photometry measured within elliptical apertures by piXedfit (blue and cyan). The smaller clump B is redder (JD1B red, JD2B pink). Photometry of the entire galaxy MACS0647 -JD lensed images JD1 and JD2 (dark and light green), including clumps A and B plus additional diffuse light, was measured by grizli with circular apertures of 0 . '' 25 radius.  \n<!-- image -->  \nThe spectroscopic redshift is slightly lower (consistent within 2 σ ) than the photometric redshifts estimated previously: z phot = 10 . 7 +0 . 6 -0 . 4 (95% C.L.) from HST imaging (Coe et al. 2013) and z phot = 10 . 6 ± 0 . 3 from JWST + HST imaging (Hsiao et al. 2023). This may be explained by the Lymanα damping wing reducing flux between 1.35 - 1.5 µ m (in the JWST F150W and HST F140W filters) more than expected for a sharp Lyman break, as assumed in the photometric redshift fitting based on spectral energy distribution (SED) modeling.  \nWe measure the emission line fluxes and report them in Table 3. To measure the fluxes, we fit each line with a Gaussian after modeling and subtracting the continuum using piXedfit (Abdurro'uf et al. 2023). The continuum model is fit to the NIRSpec spectrum while masking out the emission lines. The unresolved doublets C iii ] and [O ii ] are each fitted with a single Gaussian. Flux uncertainties are estimated using the Monte Carlo method.  \nRecently, Bunker et al. (2023) presented deeper NIRSpec spectroscopy 12 of GN-z11 at z = 10 . 603 that featured all the lines above, plus additional lines that are not detected in MACS0647-JD: Ly αλ 1216, N iv ] λ 1486, C iv λ 1549, HeII λ 1640, N iii ] λ 1748, and Mg ii λ 2800. The nitrogen lines N iv ] and N iii ] were surprising detections rarely observed in any galaxy (Cameron et al. 2023a; Charbonnel et al. 2023). The measured line fluxes were ∼ 10 -18 erg s -1 cm -2 . Nitrogen lines that strong would have also been detected in our observations of MACS0647 -JD. Note the continuum brightness of GN-z11 is comparable to JD1A (F200W AB mag 25 . 8 ± 0 . 1), so similar line fluxes would correspond to similar equivalent widths (generated by similar physical properties).", '3.1. Spectral modeling': "We perform spectrophotometric SED fitting using piXedfit (Abdurro'uf et al. 2021, 2022, 2023). This  \ncode fits the spectral continuum (with emission lines masked out) and photometry simultaneously. We use the summed spectrum and the total photometry measured with rectangular apertures resembling the NIRspec slits in the four exposures. This code uses Flexible Stellar Population Synthesis ( FSPS ; Conroy et al. 2009; Leja et al. 2017) SED models, which have nebular emission incorporated using Cloudy (Ferland et al. 2017). We assume a Chabrier (2003) initial mass function, Charlot & Fall (2000) dust attenuation law, and the intergalactic absorption based on Inoue et al. (2014) model. The dust optical depth is denoted ˆ τ 2 . We assume a double power-law star formation history (SFH) with rising slope β , declining slope α , and timescale τ : SFR( t ) = [( t/τ ) α +( t/τ ) -β ] -1 . Please refer to Abdurro'uf et al. (2023, Table 2 therein) for more information on the definition of these parameters and associated priors.  \nGas-phase metallicity Z gas and stellar metallicity Z ∗ are modeled independently. To reduce the number of free parameters, we fix the ionization parameter log( U ) = -2 . 0 and the gas-phase metallicity Z gas to 12+log(O/H) = 7 . 5 based on our estimate from emission lines (see § 3.6, § 3.5 and Table 7). Varying these values within the uncertainties does not significantly change the results that follow.  \nFirst, we use piXedfit to fit the spectral continuum after masking out the emission lines. Then we subtract this best-fit continuum and fit Gaussians to the emission lines to measure their fluxes and equivalent widths, reported in Table 3.  \nThe spectrum has no Balmer break with F ν (4200 ˚ A) /F ν (3500 ˚ A) ∼ 0 . 77 ± 0 . 06, measured as in Binggeli et al. (2019), suggesting a young age. Spectral continuum fitting suggests a very young mass-weighted age of 8 +3 -2 Myr for component A. However, these spectral models do not account for the Lymanα damping wing. SED fitting to the photometry ( § 3.2) yields a similarly young age until we omit the F150W flux measurement affected by the Lyman damping. Our measured photometry is also slightly redder than the spectrum, contributing to slightly older age measurements, though still young as we discuss next in § 3.2.", '3.2. Photometric SED modeling': "We perform spectral energy distribution (SED) fitting to the NIRCam photometry of the brightest lensed image JD1 (magnified by µ = 8 ± 1) for the full galaxy and then for the individual clumps A and B, as reported in Table 2. We exclude the F150W photometry  \nbecause our spectral models do not include Lymanα damping wing. (Including the F150W photometry results in artificially low ages.) We perform SED modeling using 3 methods: piXedfit (Abdurro'uf et al. 2021, 2022, 2023); bagpipes 13 (Carnall et al. 2018, 2019); and beagle (Chevallard & Charlot 2016). We describe our methods in § 3.1 for piXedfit and below for bagpipes and beagle . We summarize our results in Table 4.  \nOur bagpipes (Carnall et al. 2018, 2019) method is described in detail in Hsiao et al. (2023). Briefly, we use Binary Population and Stellar Synthesis (BPASS) v2.2.1 templates (Stanway & Eldridge 2018) including binary evolution, with a Kroupa (2001) IMF and upper mass cutoff of 300 M ⊙ . Nebular emission is included by processing these stellar models through the photoionization code Cloudy (Ferland et al. 2017). Dust attenuation is modeled with the Salim et al. (2018) flexible parameterization, including a variable slope and additional dust within star-forming regions < 10 Myr old. Based on our spectroscopic results below, we fix gas metallicity to Z gas = 0.1 Z ⊙ and ionization parameter log( U ) = -2 (see § 3.5). Varying these values within their uncertainties does not significantly affect our derived physical parameters.  \nWe explore various star formation histories: constant, 'delayed τ ', and non-parametric. The delayed τ SFH allows for a linear rise followed by an exponential decline: SFR( t ) ∝ t exp( -t/τ ). Most of our fits only have the linear rise with τ > 1 Gyr. We explore non-parametric star formation histories with constant SFR in 4 time bins (e.g., 0 - 10 - 50 - 150 - 300 Myr). With these models, we find almost all the SFR ends up in our youngest bin 0 - 10 Myr, with negligible older populations.  \nWe also use beagle (Chevallard & Charlot 2016) to derive an independent fit to both the photometry and the measured emission line equivalent widths (see Table 3). beagle assumes a Chabrier (2003) IMF and also uses Cloudy to account for nebular emission. We further assume a delayed τ SFH with an ongoing starburst over the last 10 Myr, an SMC dust attenuation law, and the Inoue et al. (2014) IGM attenuation models. We apply a similar setup and and parameter space as in Furtak et al. (2023), though without the external priors and fixing the redshift to the measured spectroscopic value. Here we also leverage the additional information provided by the numerous emission lines to also leave the gas-phase metallicity and the dust-to-metal ratio as free parameters. These are modeled with uniform pri-  \nTable 4. Physical properties of JD1, JD1A, JD1B from SED fitting using various methods  \nrs log( Z gas / Z ⊙ ) ∈ [ -2 . 2 , -0 . 3] and ξ d ∈ [0 . 1 , 0 . 5] as in Gutkin et al. (2016) and Chevallard & Charlot (2016).  \nBased on these various methods, we obtain results summarized in Table 4. We find MACS0647 -JD has a stellar mass log( M ∗ / M ⊙ ) = 8 . 1 ± 0 . 3; SFR 10 ± 3 M ⊙ yr -1 ; and high sSFR ∼ 80 Gyr -1 , where the specific star formation rate sSFR = SFR / stellar mass.  \nThe clump A photometry can be well fit by constant star formation for 17 +5 -4 Myr, corresponding to massweighted ages 8 +3 -2 Myr, according to bagpipes . Age estimates from the various methods range between 1 50 Myr, consistent with the results from Hsiao et al. (2023). We estimate clump A contains about 1/3 the stellar mass of MACS0647 -JD.  \nThe smaller redder component B photometry is best fit by a linearly rising SFR for 40 - 300 Myr, with a massweighted age 10 - 110 Myr, stellar mass log( M ∗ / M ⊙ ) = 7 . 9 ± 0 . 3, and dust A V = 0 . 10 ± 0 . 05 mag. Based on similar age estimates in Hsiao et al. (2023), they suggested clump B may have formed separately and merged with the younger clump A, though different star formation histories in situ are also possible.  \nMACS0647 -JD has an absolute UV magnitude M UV = -20 . 3 ± 0 . 2, including M UV = -19 . 5 ± 0 . 2 for clump A and M UV = -17 . 9 ± 0 . 2 for clump B. These  \nare based on the JD1 F200W photometry in Table 2 delensed by a magnification µ = 8 ± 1.", '3.3. Star formation rate and history': 'Hydrogen Balmer line strengths yield robust estimates of recent star formation history within the past ≲ 10 Myr. These measurements commonly utilize the strongest Balmer line H α or the second strongest H β (e.g., Glazebrook et al. 1999; Erb et al. 2003; Reddy et al. 2008; Madau & Dickinson 2014; Shapley et al. 2023). Both of these are redshifted beyond our observed wavelength range, however we detect both H γ and H δ .  \nIntrinsic Balmer line strength ratios are dictated by atomic physics. For Case B recombination at T = 10000K, we expect H γ / H δ = 1 . 81 (e.g., Dopita & Sutherland 2003; Groves et al. 2012). In MACS0647 -JD, we measure H γ / H δ ∼ 1 . 88 ± 0 . 43, consistent with expectations (H γ / H δ = 1 . 81) within the uncertainties. Dust reddening may artificially increase observed Balmer line ratios. We cannot place meaningful constraints on the dust extinction, given the large uncertainties in the flux ratio and the similar wavelengths of H γ and H δ . Note that Balmer line stellar absorption might affect our measurement of H γ and H δ of  \nTable 5. Derived emission line ratios and expected values  \n0 -5 ˚ A, which is within our uncertainty of 6 ˚ A. We assume no dust, consistent with the result A V < 0 . 02 mag from SED fitting to the photometry of component A in Hsiao et al. (2023) and similarly in our updated analysis of the latest photometry § 3.2. Finally, we note the measured H γ rest-frame equivalent width EW 42 ± 6 ˚ A may be slightly suppressed by photospheric absorption lines with EW < 5 ˚ A, but that is within our measurement uncertainty.  \nAssuming no dust, we estimate the H β and H α line fluxes using the expected line ratios H β = 2.14 H γ and H α = 6.11 H γ (see Table 5). Converting our inferred H α line flux to luminosity, including a de-lensing correction for magnification, we estimate L H α = (4 . 5 ± 0 . 2) × 10 41 erg s -1 . Adopting an SFR conversion factor of 3.2 × 10 -42 suitable for high-redshift galaxies (Reddy et al. 2018), we estimate SFR = 1 . 4 ± 0 . 2 M ⊙ yr -1 . Note that the SFR will be higher if there is dust, and the conversion factor is sensitive to the IMF, star formation history, and metallicity assuming that the escape fraction is zero (e.g., Wilkins et al. 2019). Also, the SFR derived from the emission lines is smaller than the estimates from the photometry of JD1, but it is consistent with the SFR estimated from the photometry of JD1A. This is likely because the slitlets of four observations mainly targeted JDA (see Figure 1).  \nSimilarly, [O ii ] λ 3727 can also be used to estimate the SFR for distant galaxies (e.g., Kennicutt 1998). This yields a slightly lower SFR OII = 0 . 6 ± 0 . 2 M ⊙ yr -1 . However, we note that this empirical calibration was derived for low-redshift galaxies and depends on metallicity and dust, which are lower for high-redshift galaxies like MACS0647 -JD.', '3.4. Strong C iii ] λλ 1907,1909 emission': "We detect strong emission of C iii ] λλ 1907,1909 (blended) with a line flux of (3 . 1 ± 0 . 6) × 10 -18 erg s -1 cm -2 and rest-frame equivalent width 14 ± 3 ˚ A. Such high equivalent width C iii ] λλ 1907,1909 is associated with low metallicity galaxies experiencing an intense burst of star formation (Rigby et al. 2015); it is predicted for BPASS models (Stanway & Eldridge 2018) only when they include very recent star formation within the past Myr (Jaskot & Ravindranath 2016), consistent with our young age estimates § 3.2. We use the measured equivalent width as a metallicity diagnostic in § 3.6.  \nWe note additional C iii ] emission appears to come from the B component, which is marginally spatially resolved in the 2D spectrum of JD2 in Obs 21 (Figure 1). This would suggest a young age for B, or at least very recent star formation within the past Myr perhaps in addition to the older star formation and age ( ∼ 100 Myr) estimated from the photometry.  \nStrong C iii ] emission with high rest-frame equivalent widths of 10 - 20 ˚ A or more has been observed in z ∼ 0 - 8 galaxies, often associated with high observed or inferred [O iii ]+H β equivalent widths ∼ 1000 ˚ A - 2000 ˚ A (e.g., Stark et al. 2017; Berg et al. 2019; Hutchison et al. 2019; Mainali et al. 2020; Tang et al. 2021; Mingozzi et al. 2022; Vanzella et al. 2020a, 2023) or even higher than 2000 ˚ A (Tang et al. 2023). This is consistent with our expectation based on our extrapolated [O iii ]+H β flux (Table 5), which roughly corresponds to an equivalent width ∼ 1000 ˚ A, assuming the continuum flux at rest-frame ∼ 5000 ˚ A is similar to what we measure out to ∼ 4500 ˚ A.  \nWe do not detect the higher ionization species C iv λ 1549. This combined with the strong C iii ] emis-  \nion suggests that an AGN is likely not the driving ionizing source in this galaxy. Detections of strong C iv are often associated with AGN activity (e.g., Baskin & Laor 2005; Le F'evre et al. 2019). However, young stellar populations can also drive stronger C iv emission as well (e.g., Mainali et al. 2017).  \nIf anything, we see a hint of C iv absorption, as also predicted by our piXedfit best-fit model. Such C iv absorption is observed (and modeled) for young stellar populations with ages < 10 Myr (e.g., Leitherer et al. 1999; Chisholm et al. 2019) and can constrain stellar age and metallicity when detected at high signal-to-noise and resolution. The ISM can also absorb C iv due to internal gas kinematics and/or higher column density (Steidel et al. 2016; Jaskot & Ravindranath 2016).", '3.5. Ionization log( U ) and log( ξ ion )': "The line ratio O32 = [O iii ] λ 5007 / [O ii ] λ 3727 has long been used (e.g., Hicks et al. 2002) as a diagnostic for the ionization parameter log( U ). At high redshifts, when [O iii ] λ 5007 is unavailable (For example, galaxies at z ≳ 9 . 6, [O iii ] λ 5007 shifts beyond the wavelength coverage of 5.3 µ m in NIRSpec), the line ratio Ne3O2 = [Ne iii ] λ 3869 / [O ii ] λ 3727 has been proposed as an alternative diagnostic (P'erez-Montero et al. 2007; Levesque & Richardson 2014; Maiolino & Mannucci 2019; Witstok et al. 2021). Strong correlations are observed between Ne3O2 and O32 in nearby galaxies when all lines are detected with strong significance (Jaskot & Oey 2013; Izotov et al. 2018; Flury et al. 2022), especially the case for higher ionization (i.e., similar to properties of galaxies expected and found at z > 6). More distant galaxies at z ∼ 2 - 7 exhibit similar trends (Christensen et al. 2012; Tang et al. 2019; Vanzella et al. 2020b; Tang et al. 2023).  \nIn MACS0647 -JD, we measure a high value for Ne3O2 = 1 . 8 ± 0 . 2. According to Witstok et al. (2021, Equations 1-3), this Ne3O2 ratio corresponds to O32 = 30 ± 6 and ionization parameter log( U ) = -1 . 84 ± 0 . 06, using log( U ) = 0.80 × log(O32) -3.02 from (D'ıaz et al. 2000).  \nWe also used hii-chi-mistry version 5.22 14 (P'erezMontero 2014) to estimate log( U ) using the observed and extrapolated line flux ratios discussed in § 3.6 and listed in Table 6. Our inputs were measured line fluxes for [O ii ] λ 3727, [Ne iii ] λ 3869, and [O iii ] λ 4363, all normalized to our extrapolated H β flux based on H γ . Here we did not use the extrapolated [O iii ] λ 5007 flux. We obtain an ionization parameter of log( U ) = -2 . 09 ± 0 . 02,  \nsimilar to but slightly lower than the value estimated above from Ne3O2.  \nKewley et al. (2019) noted the line ratio C iii ] λλ 1907,1909 / [C ii ] λ 2325 (blend) could be an excellent diagnostic for ionization parameter log( U ) at low metallicities 12+log(O/H) < 8 . 5 (see their Figure 7). Our non-detection of [C ii ] with flux < 0 . 55 × 10 -18 erg s -1 cm -2 (1 σ limit), yielding a line ratio C iii ] / [C ii ] > 5 . 7 corresponds to log( U ) > -2 . 8 for 12+log(O/H) ∼ 7.6.  \nWe conclude log( U ) = -1 . 9 ± 0 . 2 based on the three estimates (see also Table 7). This is comparable to the value log( U ) ∼ -2 obtained for GN-z11 (Bunker et al. 2023).  \nOur H α luminosity measurement (delensed and assuming no dust) yields an estimate for the production rate of hydrogen-ionizing photons: ˙ N ion = (3.3 ± 0 . 1) × 10 53 s -1 (log( L H α ) = log( N ion / s) -11 . 87). Assuming the escape fraction is zero, combined with our measured and demagnified UV luminosity for clump A (corresponding to M UV = -19 . 5 ± 0 . 2), we estimate an ionizing photon production efficiency ξ ion = ˙ N ion /L UV ν = 1 . 6 ± 0 . 3 × 10 25 erg -1 Hz, or log( ξ ion ) = 25 . 2 ± 0 . 2. This is consistent with predictions for highredshift galaxies ( z > 8), with higher values expected for younger ( ≲ 10 8 yr), lower-metallicity galaxies ( Z ≲ Z ⊙ ) (e.g., Schaerer 2003; Robertson et al. 2013; Wilkins et al. 2016). Observationally, recent JWST studies reported higher values log( ξ ion ) ∼ 25 . 7 -26 . 0 erg -1 Hz for highredshift (7 < z < 11) galaxies (e.g., Tang et al. 2023; Bunker et al. 2023; Fujimoto et al. 2023). Our ˙ N ion estimate should be treated as a lower limit that could increase due to dust and/or escape fraction f esc .", '3.6. Metallicity': "We use various methods and line ratio diagnostics to estimate MACS0647 -JD's gas-phase metallicity 12+log(O/H) = 7.5 - 8.0, or (0.06 - 0.2) Z ⊙ , where we adopt a solar metallicity 12+log(O/H) = 8.69 (Asplund et al. 2021). Table 6 summarizes our results, and we describe our methods below.  \nThe auroral line [O iii ] λ 4363 can provide a 'direct' metallicity measurement via electron temperature when detected and measured along with other lines including [O iii ] λ 4959, λ 5007 (e.g., Peimbert 1967; Osterbrock 1989; Sanders et al. 2024). Given our estimate O32 = 30 ± 6 ( § 3.5) and observed line flux for [O ii ], we can estimate the expected [O iii ] λ 5007 line flux as (1 . 3 ± 0 . 3) ×  \nTable 6. Metallicity Estimates  \nTable 7. Physical properties of MACS0647 -JD (entire galaxy) and individual clumps A and B, estimated based on observed and estimated line fluxes and SED fitting to the photometry. Star formation rate (average within the past 10 Myr) and stellar mass are corrected for lensing magnification.  \nNote . BAGPIPES assumes Kroupa et al. (1993); to renormalize those results, we multiplied the stellar masses by 0.94 (Madau & Dickinson 2014).  \n10 -17 erg s -1 cm -2 , assuming no dust, or ∼ 50 times stronger than [O iii ] λ 4363. Note the [O iii ] λ 5007 line is 2.98 times stronger than [O iii ] λ 4959 (Storey & Zeippen 2000), so our extrapolated combined [O iii ] λ 4959, λ 5007 flux is 1.34 times the [O iii ] λ 5007 flux.  \nWe use pyneb (Luridiana et al. 2015) to analyze the observed and extrapolated emission line ratios. For the entire procedure, we assumed no dust and an electron density n e = 100 cm -3 . First, we use the task getCrossTemDen , taking into account the [O iii ] λ 5007 / 4363 ∼ 50 with a 20% uncertainty. In this way, we obtain the electron temperature of the high-ionization zone T e ([O iii ]) = 15000 ± 1400 K. The T e uncertainty is  \nestimated by running the task 1000 times and taking the standard deviation of all the values. Then, we use the Garnett (1989) relation to estimate the low-ionization gas temperature T e ([N ii ]) = 13600 ± 1000 K. Finally, we calculated the O ++ and O + ionic abundances with the task getCrossTemDen , using as input [O iii ] λ 5007 / H β ∼ 8 and T e ([O iii ]), and [O ii ] λ 3727 / H β ∼ 0.26 and T e ([N ii ]), respectively, with the same method to estimate the uncertainties. The total of both species yields 12+log(O/H) = 8 . 0 ± 0 . 2, or ∼ 20% Z ⊙ (0.13 - 0.32 Z ⊙ ).  \nWe also utilize hii-chi-mistry version 5.22 to analyze our observed line ratios, as described in § 3.5.  \nWe obtain 12+log(O/H) ∼ 7 . 5 ± 0 . 2, corresponding to ∼ 0 . 06 +0 . 04 -0 . 02 Z ⊙ .  \nNext, we turn to line ratio diagnostics, beginning with Ne3O2. Previous reviews find no strong correlation between Ne3O2 and metallicity, as seen, for example, in local metal-poor galaxies ( Z < 0 . 6 Z ⊙ ) analyzed by Nakajima et al. (2022, Figure 9 therein). But the few galaxies with high Ne3O2 ∼ 2 in that study were clustered between roughly 12+log(O/H) = 7 . 6 ± 0 . 2, or 0.05 - 0.13 Z ⊙ . It is unclear if that low-redshift result ( z < 0 . 1) can be extended to high-redshift galaxies.  \nAnother metallicity diagnostic is the line ratio R23 = ([O iii ] λ 4959, λ 5007+ [O ii ] λ 3727) / H β (e.g., Nakajima et al. 2022; Sanders et al. 2024). Based on our observed [O ii ], extrapolated [O iii ], and H β inferred from H γ , we extrapolate R23 = 11 ± 3. This is among the highest values measured for local metal-poor galaxies by Nakajima et al. (2022). That puts R23 ∼ 11 in the zone of confusion in the bimodal R23-metallicity relation, severely limiting its usefulness as a metallicity diagnostic, though it can still provide a rough estimate. We note in Nakajima et al. (2022, Figure 3), that galaxies with R23 = 11 ± 3 have metallicities 12+log(O/H) = 8 . 0 ± 0 . 3, or between ∼ 0.1 and 0.4 Z ⊙ . We note some of the scatter in the R23 vs. Z is due to ionization, with higher ionization yielding higher R23 values for a fixed metallicity (e.g., P'erez-Montero 2014, Figure 5).  \nIzotov et al. (2021) propose a metallicity indicator combining R23 and O32 (their Equation 5) for improved accuracy at low metallicities < 6% Z ⊙ , or 12+log(O/H) < 7 . 5. Nakajima et al. (2023) show this relation works up to 12+log(O/H) ∼ 7.8 for z = 4 - 8.5 galaxies with direct metallicity measurements from NIRSpec. For MACS0647-JD, this relation yields 12 + log(O/H) ∼ 7 . 7 ± 0 . 2, or 0.06 - 0.16 Z ⊙ .  \nWe find broad general agreement among our 6 metallicity indicators with best-fit estimates ranging between 12+log(O/H) = 7.5 - 8.0, or (0.06 - 0.2) Z ⊙ , as summarized in Table 6, which is also consistent with the metallicity of 12+log(O/H) = 7-7.8 expected from Astraeus simulations for galaxies at z ∼ 10 with a stellar mass of 10 8 . 1 M ⊙ (Ucci et al. 2023). This is promising for future studies that only have one or more of these diag-  \nFinally, we use the rest-frame UV line C iii ] λλ 1907,1909 as a metallicity diagnostic. Mingozzi et al. (2022) analyzed 45 local ( z < 0 . 2) high-redshift analogs observed by the CLASSY survey (Berg et al. 2022), measuring a relation between C iii ] EW and metallicity with 0.18 dex intrinsic scatter for galaxies with EW > 5 ˚ A. Using their equation 7 and our observed C iii ] EW 14.2 ± 2 . 5 ˚ A (discussed in § 3.4), we estimate 12+log(O/H) = 7 . 84 ± 0 . 18, or 0.09 - 0.21 Z ⊙ .  \nnostics available either in the rest-frame optical or restframe UV. On the other hand, greater precision will be achieved by generally improving these diagnostics and in our specific case by obtaining additional spectra of MACS0647 -JD covering longer wavelengths including [O iii ] λ 4959, λ 5007, H β , and H α .", '3.7. Lymanα damping wing': "The Lymanα photon scattering cross section as a function of wavelength is given by the Voigt profile, which combines a Gaussian core and Lorentzian wings (Tasitsiomi 2006). Resonant scattering of Lymanα photons by the neutral IGM suppresses line and continuum fluxes at wavelengths bluer than the rest-frame Lymanα at 1216 ˚ A. Additionally, the Lorentzian wing cross section accumulates the attenuation to the redward continuum, softening the shape of Lymanα break. This is known as Lymanα damping wing attenuation (MiraldaEscud'e 1998). Features like these have been observed in quasars (e.g., Mortlock et al. 2011; Ba˜nados et al. 2018; Davies et al. 2018; Wang et al. 2020; Yang et al. 2020), and they have been utilized to investigate not only the average neutral fraction but also specific regions along different sightlines in the IGM at z > 7. Recently, this effect has been observed in NIRSpec prism observations of high-redshift galaxies ( z > 8; Bunker et al. 2023; Boyett et al. 2024; Arrabal Haro et al. 2023a,b; CurtisLake et al. 2023)  \nWe model the Lymanα damping wing optical depth following Equation (30) in Dijkstra (2014), as done in Arrabal Haro et al. (2023a,b). The Lymanα damping wing description has two free parameters (with redshift held fixed at our measured z = 10 . 17): (1) the neutral hydrogen fraction in the IGM ( X HI ) and (2) the size of the ionized bubble ( R HII ), or Stromgren sphere. In short, a higher neutral fraction in the IGM makes the break cutoff become smoother, and a larger ionized bubble size shifts the break blueward allowing the escape of photons at shorter wavelengths than the rest frame Lymanα . To reproduce the observed continuum spectrum, the galaxy model SEDs are convolved with the IGM transmission ( T IGM ∝ e -τ , where τ is damping wing optical depth). We then smooth the model spectra with prism spectral resolution and apply an additional 5% of systemic errors in the χ 2 estimation.  \nWe perform fitting using an MCMC sampler package described in Jung et al. (2017). We use flat linear priors for the free parameters X HI and R HII . In each MCMC chain step, we take a random model spectrum from the range of models generated by piXedfit (see § 3.2) to accommodate the uncertainties in galaxy SED modeling. The wavelength range of the spectrum fitted by  \nFigure 4. Top: Lymanα damping wing analysis of MACS0647-JD without a damped Lymanα (DLA) contribution. The left panel shows the piXedfit SED model (blue) convolved with the IGM transmission and NIRSpec prism spectral resolution, resulting in the transmitted model spectrum (red). The vertical dotted line denotes the systemic wavelength of Lymanα at z = 10 . 17. The right panel displays 1 σ , 2 σ , and 3 σ contours of the probability distribution of X HI and R HII . The best fit suggests a highly neutral IGM ( X HI > 0 . 9 at a 1 σ lower limit) with a small ( R HII < 0 . 2 pMpc) ionized bubble around MACS0647 -JD although the modeled spectra show a still considerably steeper break than observed (black). Bottom: Lymanα damping wing analysis with a DLA system. The inclusion of a DLA contribution better reproduces the observed Lymanα break shape (left panel). However, the H I column density of the DLA ( n HI ) is highly degenerate with the neutral IGM fraction, making it highly unconstrained.  \n<!-- image -->  \npiXedfit is between 1 . 5 -5 . 2 µ m and the fitting does not include the modeling of the absorption by Damped Lymanα . The inclusion of the additional attenuation by an immediate Damped Lymanα can reproduce the observed spectra well as in Heintz et al. (2024).  \nFigure 4 shows our results suggesting a small size of an ionized bubble ( R HII ≪ 1 pMpc) with a highly neutral IGM ( X HI > 0.9 at a 1 σ lower limit). We experiment with different priors on X HI , including simply assuming a completely neutral IGM ( X HI = 1) as inferred from other work (e.g., Barkana & Loeb 2001; Treu et al. 2013; Mason et al. 2018; Bruton et al. 2023), and a logarithmic prior. These priors do not significantly affect our bubble size estimates.  \nThe R HII estimate appears reliable in the sense that the observed spectra show no positive signals blueward of the systemic wavelength of Lymanα . However, the interpretation of the X HI measurement is rather compli-  \nated. The modeled spectra present a Lymanα break still considerably steeper than the observed spectrum. As the modeled spectra already include Lymanα damping wing opacity with almost fully-neutral IGM, such discrepancies cannot be explained with the IGM attenuation alone. In fact, the total Lymanα optical depth combines the IGM damping wing optical depth ( τ IGM ) and the optical depth due to resonant scattering within the circumgalactic (CGM; Dijkstra 2014). However, the latter part is missed in our simple description of damping wing opacity. To mitigate the differences between the modeled spectra and the observed, it is necessary to carefully model the CGM contribution (Sadoun et al. 2017; Weinberger et al. 2018; Mason & Gronke 2020). Including the CGM contribution would result in additional softening on Lymanα break closer to the observed spectrum, which possibly requires less contribution from  \nIGM attenuation and could allow for a slightly more ionized IGM.  \nWe attempt to model the spectra with a damped Lyman-alpha (DLA) system, following the approach in Heintz et al. (2024). The results with the DLA contribution are shown at the bottom of Figure 4. The inclusion of a DLA better reproduces the observed spectrum, with a DLA H I column density of log( n HI , cm -2 ) = 21 . 9 ± 0 . 2, comparable to Heintz et al. (2024). This analysis reveals that the IGM damping wing attenuation is highly degenerate with the effect of DLA systems. Consequently, including DLAs makes the neutral hydrogen fraction highly unconstrained (bottom right in Figure 4). However, this improved fit underscores the complexity of disentangling the contributions from DLAs and the IGM in such high-redshift observations. However, detailed modeling of Lymanα attenuation of the CGM requires knowledge of density profiles of H I gas and radiation field from a host galaxy (Weinberger et al. 2018; Mason & Gronke 2020), which is beyond the scope of this study. Also, the relation between IGM attenuation and bubble size can deviate from the theoretical model of Dijkstra (2014) due to the stochasticity of individual sightlines, such as fluctuations in density/velocity and random encounters of self-shielded systems (Hutter et al. 2014; Park et al. 2021; Smith et al. 2022). Ideally, one needs to average over a large number of observations to suppress such uncertainties. Additionally, the uncertainties in modeling intrinsic rest-UV spectra make the interpretation more complicated.", '3.8. Ionized bubble size': "We also estimate the radius of the ionized bubble around MACS0647 -JD by integrating the total ionizing photon production over the galaxy's lifetime as in Shapiro & Giroux (1987):  \n4 3 πR 3 HII ∼ ˙ N ion f esc t ∗ X HI n H . (1)  \nWe estimate ˙ N ion ∼ 3.3 × 10 53 s -1 based on SFR ∼ 1.4 M ⊙ yr -1 for clump A ( § 3.5) with stars having formed continuously for perhaps t ∗ ∼ 20 Myr ( § 3.2). The average density of hydrogen particles in the universe at z = 10 . 17 is n H ∼ 7 × 10 69 Mpc -3 , where n H = (1 -Y He ) ρ crit Ω b (1 + z ) 3 m -1 H . And here we assume a neutral IGM ( X HI = 1).  \nWe do not estimate f esc for MACS0647 -JD in this work. Here, it suffices to explore possible values. For example, f esc = 10% yields R HII ∼ 0.09 pMpc. A more extreme f esc = 50% would only increase that to R HII ∼ 0.15 pMpc.  \nAbove, we use the SFR for clump A. The entire galaxy has SFR ∼ 10 M ⊙ yr -1 , or ∼ 7 × higher. We might expect that most of the ionizing radiation comes from the blue clump A. But even generously assuming the same ionizing photon production efficiency ξ ion for the entire galaxy and increasing ˙ N ion by 4 × , R HII only increases by a factor of ∼ 1.6 to R HII ∼ 0.24 pMpc, again assuming a very high f esc = 50%.  \nWe note these are only rough estimates subject to significant uncertainties. Dense neutral gas clouds in the IGM may impede the expansion of the reionized bubble. Some of the reionized gas may recombine, further reducing the bubble size, especially if the ionizing flux wavers due to variations in SFR or f esc .  \nOn the other hand, the total ionizing flux might be much stronger than we have estimated here due to fainter undetected companions, especially given that MACS0647 -JD is a merger.", '3.9. Candidate companion galaxy C': "As discovered in Hsiao et al. (2023), a nearby triplylensed J-band dropout galaxy is suspected to be a companion of MACS0647 -JD ∼ 3 kpc away. The photometric redshift and geometric lens model redshift of this companion 'C' are consistent with MACS0647 -JD of 10.17; the observed lensed positions require a similar or identical redshift. Here we show the NIRSpec spectra of the candidate companion C in Figure 5 and the 1D sum in Figure 6. The Obs 21 spectrum shows a clear Lyman break consistent with z = 10 . 17. The Obs 23 spectrum is noisier but also consistent with the redshift of MACS0647-JD ( z = 10 . 17). This supports our conclusion from Hsiao et al. (2023) that MACS0647 -JD is likely the most distant galaxy merger known at z = 10 . 17, including two merging components A and B plus a third component C nearby, where component C may indeed be a companion of A and B components.  \nGiven the lower SNR spectrum of the companion C, we do not detect emission lines, nor do we detect the Lymanα damping wing expected due to the proximity to A.", '4. CONCLUSIONS': "In this study, we report NIRSpec prism observations of MACS0647-JD, primarily targeting its small component Awith delensed radius r ∼ 70 pc. We measure a spectroscopic redshift z = 10 . 17 based on detections of 7 emission lines: C iii ] λλ 1907,1909, [O ii ] λ 3727, [Ne iii ] λ 3869, [Ne iii ] λ 3968, H δ , H γ , and [O iii ] λ 4363.  \nThis redshift is slightly lower than the photometric redshifts z ∼ 10 . 6 estimated previously based on HST and JWST + HST imaging. This may be explained by a  \nFigure 5. NIRSpec prism spectra of two lensed images of the candidate companion galaxy C. Figures show slitlet coverages, 2D spectra, and 1D extractions, similar to Figure 1 for MACS0647 -JD. Redshift is fixed to the same value z = 10 . 17.  \n<!-- image -->  \nLymanα damping wing revealed by NIRSpec that suppresses the photometry at ∼ 1.5 µ m more than expected for a sharp Lyman break. Based on observed and extrapolated line ratios of JDA, we estimate an ionization parameter log( U ) = -1 . 9 ± 0 . 2, and ionizing photon production efficiency log( ξ ion ) = 25 . 2 ± 0 . 2 for clump A. This log( ξ ion ) value is similar to values measured in subL ∗ z ∼ 4 - 5 galaxies (Bouwens et al. 2016) but lower than measured in z ∼ 7 - 8 galaxies: log( ξ ion ) = 25.7 26.0 (Tang et al. 2023).  \nBased on the observed and extrapolated line ratios of JDA, we also estimate a gas phase metallicity 12+log(O/H) = 7.5 - 8.0, or (0.06 - 0.2) Z ⊙ derived using 6 different methods, including optical line diagnostics as well as one diagnostic based on the restUV line C iii ] (Mingozzi et al. 2022). Derived metallicities are consistent across different methods. The overall agreement is encouraging, supporting the use of each individual method in galaxies with fewer detected emission lines. Additional MIRI spectroscopy covering [O iii ] λ 4959, λ 5007, H β , and H α would enable a more precise 'direct' metallicity measurement when combined with the other lines presented here, including the auroral line [O iii ] λ 4363.  \nThe total stellar mass of MACS0647 -JD is log( M/M ∗ ) = 8 . 1 ± 0 . 3 based on SED fitting to the pho-  \netry of the entire galaxy including both clumps A and B. This is towards the low end of stellar masses for z = 4 - 10 galaxies with direct metallicity estimates from JWST NIRSpec spectroscopy (Nakajima et al. 2023). The metallicity of MACS0647 -JD at z = 10 . 17 (if we assume the metallicity of clump A is representative of the whole galaxy) is consistent with the metallicities measured for 4 < z < 10 galaxies of similar stellar mass.  \nMACS0647 -JD has a delensed absolute UV magnitude M UV = -20 . 3 ± 0 . 2, including M UV = -19 . 5 ± 0 . 2 for clump A and M UV = -17 . 9 ± 0 . 2 for clump B. SED fitting to the observed photometry of clump A yields a stellar mass log( M/M ∗ ) = 7 . 8 ± 0 . 3, likely all produced within the most recent 20 Myr. This young age estimate is supported by the observed strong C iii ] λλ 1907,1909 with rest-frame equivalent width 14 ± 2 ˚ A. The star formation rate of clump A based on H γ and assuming no dust is 1 . 4 ± 0 . 2 M ⊙ / yr over the past 10 Myr. This is similar to the estimate 2 ± 1 M ⊙ / yr based on SED fitting to clump A's photometry.  \nClump B is likely older with a rising star formation history over ∼ 50 Myr or more, stellar mass log( M/M ∗ ) = 7 . 8 ± 0 . 3, and 0 . 13 ± 0 . 07 mag dust. The older age of clump B suggests it may have merged with clump A rather than the two clumps forming together in the same galaxy (Hsiao et al. 2023). Spectroscopy of a nearby  \nFigure 6. sum of the spectra shown in Figure 5 for two lensed images of the candidate companion galaxy C. No emission lines are confidently detected; their expected wavelengths are labeled assuming a redshift z = 10 . 17 as derived for MACS0647 -JD.  \n<!-- image -->  \ngalaxy C ∼ 3 kpc away (delensed) reveals a Lyman break consistent with MACS0647 -JD's redshift z = 10 . 17. This companion C may be destined to merge with A and B. MACS0647 -JD is likely the most distant galaxy merger yet known.  \nEmission line spectroscopy is possible for the triplylensed galaxy MACS0647 -JD thanks to its 3 images magnified by factors ∼ 8, 5, and 2. The brightest lensed image JD1 is F200W AB mag 25 . 0 ± 0 . 1, including AB mag 25 . 8 ± 0 . 1 for clump A. Of all known z > 10 galaxies, only GN-z11 at z = 10 . 603 (Bunker et al. 2023) is similarly bright (F200W AB mag 26 . 0 ± 0 . 1; Tacchella et al. 2023), while most others are AB mag 28 - 29 (Curtis-Lake et al. 2023; Arrabal Haro et al. 2023a). MACS0647 -JD and GN-z11 offer unique opportunities for detailed studies of galaxies within the first 500 Myr.  \nMany of the physical properties presented in this work rely on extrapolations for [O iii ] λ 5007, H β and/or H α line fluxes. With our granted JWST time in cy-  \n2, we will obtain MIRI MRS spectroscopy covering ∼ 5 -7 . 7 µ m of observed wavelength (rest-frame of 0 . 45 -0 . 7 µ m) which will reveal those emission lines (though H β is likely too faint for detection) and enable a more robust analysis of this galaxy. The observation will give spatially resolved spectra that cover both clumps A and B as well as component C of the JD1 system, which gives an opportunity to further confirm the merging nature of this system. In addition to this, we will also obtain high-resolution NIRSpec spectroscopy to better resolve the emission lines currently detected in our prism spectrum, enabling a better measurement of the equivalent width.", 'ACKNOWLEDGMENTS': "We thank the anonymous referee for useful comments and constructive remarks on the manuscript.  \nWe are grateful and indebted to the 20,000 people who worked to make JWST an incredible discovery machine.  \nThis work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope ( JWST ) and Hubble Space Telescope ( HST ). The data were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-03127 for JWST .  \nThese observations are associated with programs JWST GO 1433 and HST GO 9722, 10493, 10793, and 12101.  \nTH and A were funded by a grant for JWST-GO01433 provided by STScI under NASA contract NAS503127. AA acknowledges support from the Swedish Research Council (Vetenskapsr˚adet project grants 202105559). PD acknowledges support from the NWO grant 016.VIDI.189.162 ('ODIN') and the European Commission's and University of Groningen's CO-FUND Rosalind Franklin program. The Cosmic Dawn Center is funded by the Danish National Research Foundation (DNRF) under grant #140. EZ and AV acknowledge support from the Swedish National Space Agency. EZ also acknowledges grant 2022-03804 from the Swedish Research Council. MB acknowledges support from the Slovenian national research agency ARRS through grant N1-0238. TAH is supported by an appointment to the NASA Postdoctoral Program (NPP)  \nat NASA Goddard Space Flight Center, administered by Oak Ridge Associated Universities under contract with NASA. AZ and LJF acknowledge support by Grant No. 2020750 from the United States-Israel Binational Science Foundation (BSF) and Grant No. 2109066 from the United States National Science Foundation (NSF), and by the Ministry of Science & Technology, Israel. EV acknowledge financial support through grants PRINMIUR 2017WSCC32, 2020SKSTHZ and INAF 'mainstream' grants 1.05.01.86.20 and 1.05.01.86.31. EV acknowledges support from the INAF GO Grant 2022 'The revolution is around the corner: JWST will probe globular cluster precursors and Population III stellar clusters at cosmic dawn'. 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