On the origins of oxygen: ALMA and JWST characterise the multi-phase, metal-enriched, star-bursting medium within a 'normal' $z > 11$ galaxy

TL;DR

This work presents deep ALMA observations of the $z>11$ galaxy JADES-GS-z11-0, securing a robust [O III] $88\,\mu$m detection, refining the FIR redshift to $z=11.1221\pm0.0006$, and constraining dust emission with $S_\nu<9\,\mu$Jy. The galaxy comprises two compact, likely merging components with a modest stellar mass and significant oxygen enrichment, yielding $L_{[O\,III]}=(1.1\pm0.3)\times10^{8}\,L_\odot$ and $12+\log(O/H)=8.07\pm0.13$ (Z$\approx0.24\,Z_\odot$). Dust remains scarce ($M_{\mathrm{dust}}\lesssim10^{6}\,M_\odot$; $M_*/M_{\mathrm{dust}}\gtrsim 10^2$), while a substantial HI reservoir leads to $\log_{10}N_{\mathrm{H\,I}}\approx22.4$ and a gas fraction ~$f_{\mathrm{gas}}\approx0.35$, placing the system in a highly star-bursting regime with $\Sigma_{\mathrm{SFR,30}}\approx62\,M_\odot\,\mathrm{yr^{-1}\,kpc^{-2}}$. Collectively, the results demonstrate rapid metal enrichment and burst-driven star formation in a normal $z>11$ galaxy, and highlight how ALMA's oxygen line can trace recent star formation and ISM conditions at Cosmic Dawn.

Abstract

The unexpectedly high abundance of galaxies at $z > 11$ revealed by JWST has sparked a debate on the nature of early galaxies and the physical mechanisms regulating their formation. The Atacama Large Millimeter/submillimeter Array (ALMA) has begun to provide vital insights on their gas and dust content, but so far only for extreme 'blue monsters'. Here we present new, deep ALMA observations of JADES-GS-z11-0, a more typical (sub-$L^*$) $z > 11$ galaxy that bridges the discovery space of JWST and the Hubble Space Telescope. These data confirm the presence of the [O III] 88 $μ$m line at $4.5σ$ significance, precisely at the redshift of several faint emission lines previously seen with JWST/NIRSpec, while the underlying dust continuum remains undetected ($F_ν< 9.0 \, \mathrm{μJy}$), implying an obscured star formation rate (SFR) of $\text{SFR}_\text{IR} \lesssim 6 \, \mathrm{M_\odot \, yr^{-1}}$ and dust mass of $M_\text{dust} \lesssim 1.0 \times 10^{6} \, \mathrm{M_\odot}$ (all $3σ$). The accurate ALMA redshift of $z_\text{[O III]} = 11.1221 \pm 0.0006$ ($\gtrsim \! 5\times$ refined over NIRSpec) helps confirm that redshifts measured purely from the Lyman-$α$ break, even spectroscopically, should properly take into account the effects of potential damped Lyman-$α$ absorption (DLA) systems to avoid systematic overestimates of up to $Δz \approx 0.5$. The [O III] 88 $μ$m luminosity of $L_\text{[O III]} = (1.1 \pm 0.3) \times 10^{8} \, \mathrm{L_\odot}$, meanwhile, agrees well with the scaling relation for local metal-poor dwarfs given the SFR measured by NIRCam, NIRSpec, and MIRI. The spatially resolved MIRI and ALMA emission also underscores that JADES-GS-z11-0 is likely to consist of two low-mass components that are undergoing strong bursts of star formation yet are already pre-enriched in oxygen (~20-30% solar), only 400 Myr after the Big Bang.

Figures (12)

• Figure 1: NIRCam and NIRSpec/PRISM observations of JADES-GS-z11-0. a, An inverse-variance weighted stack of PSF-matched NIRCam images from all filters with firm continuum detections, starting at F182M and going redwards (see Appendix \ref{['app:Photometric_measurements']} for details). Black and white crosses show the NIRCam-based centroids of the two components (A and B) of JADES-GS-z11-0. The placement of the NIRSpec micro-shutters is shown in white (nearly identical across all visits). A horizontal bar indicates a physical scale of $1 \, \mathrm{kpc}$ at $z = 11.122$. b, One-dimensional NIRSpec/PRISM spectrum. Shading shows $1 \sigma$ uncertainty on individual wavelength bins (i.e. the covariance matrix diagonal, $\sigma_i^2 = C_{ii}$; see Appendix \ref{['app:Covariance_matrix']}). For the redshift solution $z = 11.122$ reported by 2024ApJ...976..160H, the location of key rest-frame UV and optical emission lines is indicated, most prominent among which are the C iv, [O ii], and [Ne iii] emission lines.
• Figure 2: Dust-continuum emission in JADES-GS-z11-0 as seen in the observations presented in this work (left), from all archival ALMA imaging in the HUDF 2024MNRAS.528.5019H, and a combination of the two (right; see text for details). Black crosses show the NIRCam-based centroids of the two components (A and B) of JADES-GS-z11-0, a white hatched ellipse shows the ALMA restoring beam. Black contours are drawn from $3\sigma$ with increments of $1\sigma$, not revealing any significant detections at the location of JADES-GS-z11-0.
• Figure 3: a, Spectrum of $\hbox{[O,{\sc iii}]}\xspace \, 88 \, \mathrm{\upmu m}$ in JADES-GS-z11-0 with $\Delta \nu_\text{obs} = 5 \, \mathrm{MHz}$ ($15 \, \mathrm{MHz}$) bins shown by the solid (dashed) black lines (see \ref{['ssec:Results:Line_emission']} for details). Symmetric grey shading shows $1\sigma$ uncertainty. A vertical dotted blue line shows the NIRSpec-based redshift, with a horizontal range indicating the $\pm 1\sigma$ uncertainty, while the vertical black line and fading grey shading shows the inferred ALMA redshift and corresponding uncertainty. The channel range from which the surface-brightness map is created is coloured in red (\ref{['ssec:Results:Line_emission']}). The atmospheric transmission is also indicated on the right vertical axis. b, Surface-brightness map of $\hbox{[O,{\sc iii}]}\xspace \, 88 \, \mathrm{\upmu m}$ in JADES-GS-z11-0 (\ref{['ssec:Results:Line_emission']}). Black crosses show the NIRCam-based centroids of the two components (A and B) of JADES-GS-z11-0, a white hatched ellipse shows the ALMA restoring beam. Grey (dashed) contours are drawn at (negative) $2\sigma$, continuing up to $5\sigma$ with increments of $1\sigma$. A horizontal bar indicates a physical scale of $2 \, \mathrm{kpc}$ at $z = 11.122$.
• Figure 4: a, NIRCam false-colour image, where each colour channel was constructed by stacking NIRCam filters as annotated. The placement of the NIRSpec micro-shutters is shown in white (nearly identical across all visits). Dashed coloured circles indicate the $0.3\hbox{$^{\prime\prime}$}$-diameter apertures used to extract the CIRC2 photometry. The $\hbox{[O,{\sc iii}]}\xspace \, 88 \, \mathrm{\upmu m}$ emission and the MIRI/F560W image are overlaid with red and green contours respectively, both drawn at $3\sigma$-$4\sigma$-$5\sigma$. A red (green) hatched ellipse shows the ALMA restoring beam (F560W point spread function). A horizontal bar indicates a physical scale of $1 \, \mathrm{kpc}$ at $z = 11.122$. b, Best-fit model SFHs of the two components, with shading representing $1\sigma$ uncertainty. A solid dark blue line shows the prediction by an 'attenuation-free' model 2024AA...689A.310F. The dotted black line and grey shading illustrates the rising SFH prior based on dark matter halo accretion (see text for details), scaled to the stellar mass of component A. c, SEDs of the main component (A) of JADES-GS-z11-0, as observed by NIRCam, MIRI, and NIRSpec/PRISM (\ref{['ssec:Observations:HST_JWST']}), as well as the faint neighbouring source (B) whose photometry (filter curves drawn at the bottom) is consistent with having the same redshift. The best-fit bagpipes models are shown as solid (component A) and dashed (B) coloured lines, with squares indicating the model photometry. d, Magnitude of residuals between observed and modelled flux densities inversely weighted by observational uncertainty, $|\chi|$. e, Agreement between the observed and modelled emission lines and the dust continuum at $88 \, \mathrm{\upmu m}$.
• Figure 5: Stellar velocity dispersion ($\sigma_*$) as function of stellar mass ($M_*$). Literature measurements of the $z > 11$ galaxies JADES-GS-z11-0 (this work), GHZ2 2024ApJ...977L...9Z, and JADES-GS-z14-0 2025ApJ...988...19S2025AA...696A..87C are indicated by black points. We estimated their stellar velocity dispersion by converting the measured $\hbox{[O,{\sc iii}]}\xspace \, 88 \, \mathrm{\upmu m}$ line width as in 2023AA...677A.145U. The stellar mass of JADES-GS-z11-0 shown here stretches across the best-fit value presented in this work (\ref{['tab:Source_properties']}) and the value presented in 2024ApJ...976..160H to illustrate the expected degree of systematic uncertainty. Nearby systems from the compilation in 2014MNRAS.443.1151N are shown by coloured points. This sample includes elliptical and S0 galaxies (Es/S0s), compact ellipticals (cEs), dwarf ellipticals and S0 galaxies (dEs/dS0s), ultra-compact dwarfs (UCDs), globular clusters (GCs), and dwarf spheroidals (dSphs).