Spectroscopic confirmation of four metal-poor galaxies at z=10.3-13.2

TL;DR

This study spectroscopically confirms four extremely distant galaxies at $z=10.3-13.2$ using JWST/NIRSpec, establishing their nature as metal-poor, low-mass systems with young stellar populations and negligible strong rest-frame UV emission lines. The spectra reveal a sharp Lyman dropout break consistent with a fully neutral IGM, and BEAGLE SED fitting yields metallicities of a few percent solar and modest star-formation rates, with UV slopes indicating very blue continua. By incorporating damping-wing models, the authors place constraints on the intergalactic neutral fraction $X_{\mathrm{HI}}$, highlighting the heterogeneous ionization state of the early universe and showcasing the power of JWST spectroscopy to probe both galaxy properties and IGM conditions at cosmic dawn. Collectively, the results demonstrate the rapid emergence of the first galaxies and provide unique insights into their metal deficiency, star-formation activity, and the state of reionization at $z>10$.

Abstract

Finding and characterising the first galaxies that illuminated the early Universe at cosmic dawn is pivotal to understand the physical conditions and the processes that led to the formation of the first stars. In the first few months of operations, imaging from the James Webb Space Telescope (JWST) have been used to identify tens of candidates of galaxies at redshift (z) greater than 10, less than 450 million years after the Big Bang. However, none of these candidates has yet been confirmed spectroscopically, leaving open the possibility that they are actually low-redshift interlopers. Here we present spectroscopic confirmation and analysis of four galaxies unambiguously detected at redshift 10.3<z<13.2, previously selected from NIRCam imaging. The spectra reveal that these primeval galaxies are extremely metal poor, have masses between 10^7 and a few times 10^8 solar masses, and young ages. The damping wings that shape the continuum close to the Lyman edge are consistent with a fully neutral intergalactic medium at this epoch. These findings demonstrate the rapid emergence of the first generations of galaxies at cosmic dawn.

Figures (6)

• Figure 1: NIRSpec prism$\mathrm{R} \sim 100$ spectra for the four $\mathrm{z}>10$ galaxies targeted for the first deep spectroscopic pointing of the JADES survey, JADES-GS-z10-0, JADES-GS-z11-0, JADES-GS-z12-0 and JADES-GS-z13-0. For each galaxy we display the 1D spectrum and associated $1 \sigma$ uncertainties (which are derived from standard error propagation through the reduction pipeline). In the bottom panel we show the 2D signal-to-noise ratio plot. The 2D plot is binned over four pixels in the wavelength direction to better show the contrast across the break. The inset panel in the top right-hand corner shows the NIRCam F444W filter image with the three nodding positions of the NIRSpec micro-shutter 3 -slitlet array aperture shown in green. The red dashed line shows $1215.67 \mathring{\mathrm{A}}$ at the observed redshift $\mathrm{z}_{1216}$.
• Figure 2: UV slope,$\beta$, as a function of absolute magnitude at $1500 \mathring{\mathrm{A}}$, $_{\text{UVV }}$, measured as described in Methods 2.3. These are compared to the measurements from photometrically selected high-redshift candidates. Specifically, the average $\beta$ measured from objects spanning $\mathrm{z} \sim 8-15$ at similar $\mathrm{M}_{\mathrm{UV}}$ from Cullen $+22{ }^{40}$, as well as a sample from Atek $+22{ }^{22}$ spanning $\mathrm{z} \sim 9-16$, and the sample presented in Topping+22 ${ }^{41}$ (itself collated from the samples of refs. 21 and 43 and spanning $\mathrm{z} \sim 7-11$ ). In all cases the error bars show the $1 \sigma$ measurement uncertainties, except in the case of the point showing the average UV slope from Cullen +22 . For the Cullen +22 datapoint, the point shows the inverse-variance weighted mean and standard error of $\beta$, plotted against the median $\mathrm{M}_{\mathrm{UV}}$ of their sample of 41 galaxies in their lower luminosity bin. The errorbar in $\mathrm{M}_{\mathrm{UV}}$ is $\sigma_{M A D}$ (where $\sigma_{M A D}=1.483 x M A D$ and MAD is the median absolute deviation) of the individual $\mathrm{M}_{\mathrm{UV}}$ values.
• Figure 3: BEAGLE fit to the spectral break region of JADES-GS-z11-0 (top panel), while varying the fraction of neutral Hydrogen in the IGM,$\mathrm{X}_{\mathrm{H}}$. The red line and shaded region show the extracted spectrum and per-pixel $1 \sigma$ uncertainties and the darker blue line and shaded region shows the range and median of the fitted models, respectively. The lighter blue line shows the underlying intrinsic spectrum before application of the damping wing. The bottom panel shows the 2D constraints on redshift and $\mathrm{x}_{\mathrm{H}}$, which were varied in the fit while keeping all other physical properties constant (see text for details). For this test, we use a spectral extraction over 3 pixels that maximises the S/N in the region of the break. The shape of the damping wing is not sensitive to wavelength-dependent slit losses introduced by such a small extraction box since the wing it extends over just tens of pixels.
• Figure 4: Extended Data Fig. 2| The results of full spectral fitting to JADES-GS-z10-0 (top left), JADES-GS-z11-0 (top right) and JADES-GS-z12-0 (bottom) with BEAGLE. We fit models to spectra extracted over the full shutter aperture to minimise the wavelength-dependent losses due to varying point-spread function (PSF). The triangle plot shows the 2D (offdiagonal) and 1D (along the main diagonal) posterior probability distributions on stellar mass (M), metallicity (Z), maximum age of stars ( t ) and the effective dust attenuation optical depth in the V -band ( $\hat{\tau}_{\mathrm{v}}$ ) which are all derived from the beagle fits. We also include the model constraints on the star-formation rate ( $\Psi$ ), UV slope ( $\beta$ ) and ionising photon emissivity ( $\xi_{\text{ion }}$ ), which are derived parameters of the model. The dark, medium and light blue contours show the extents of the 1,2 and $3 \sigma$ credible regions of the posterior probability, respectively. The inset panel shows the observed spectrum and $1 \sigma$ standard errors per pixel in red and light red respectively, and the median and $1 \sigma$ range in fitted model spectra in blue. We fit with a constant star formation history (more details in the text and Methods section 3).
• Figure 5: Extended Data Fig. 3 I As for Extended Data Figure 2, but for BEAGLE fits to JADES-GS-z13-0. The bottom right panel shows the observed photometry and associated as blue diamonds and associated $1 \sigma$ s.d. error-bars while the coral shaded regions show the model photometry in the same bands. Since this galaxy is very close to the edge of the shutter, we use an extraction over 3 pixels to maximise the S/N. Then to account for wavelength-dependent slit losses we simultaneously fit the spectrum and NIRCam photometry.