[Paper Review] The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?

Stefano Carniani, Francesco D’Eugenio+26 more|arXiv (Cornell University)|Sep 30, 2024

Galaxies: Formation, Evolution, Phenomena4 citations

TL;DR

This study presents the first spectroscopic confirmation of a luminous galaxy at z ≈ 14.18, using ALMA and JWST/NIRSpec data to reveal strong [O III] 88 μm emission and a high metallicity (>0.1 Z☉), despite weak UV lines. The galaxy exhibits a low gas fraction (≈0.2), high ionizing photon escape fraction (20%), and low electron density (≤400 cm⁻³), suggesting radiation-driven outflows cleared the gas, enabling efficient feedback and early metal enrichment in the cosmic dawn.

ABSTRACT

JADES-GS-z14-0 is the most distant spectroscopically confirmed galaxy yet, at $z>14$. With a UV magnitude of -20.81, it is one of the most luminous galaxies at cosmic dawn and its half-light radius of 260 pc means that stars dominate the observed UV emission. We report ALMA detection of [OIII]88$μ$m line emission with a significance of 6.67$σ$ and at a frequency of 223.524~GHz, corresponding to a redshift of $14.1796\pm0.0007$, which is consistent with the candidate CIII] line detected in the NIRSpec spectrum. At this spectroscopic redshift, the Lyman-$α$ break identified with NIRSpec requires a damped Lyman-$α$ absorber with a column density of $\log(N_{ m HI}/\mathrm{cm}^{-2})=21.96$. The total [O\,{\sc iii}]88$μ$m luminosity (log$(L_{ m [OIII]}/L_\odot) = 8.3\pm 0.1$) is fully consistent with the local $L_{ m [OIII]}-SFR$ relation and indicating a gas-phase metallicity $>0.1~{ m Z_{ m \odot}}$. Using exttt{prospector} SED modeling and combining the ALMA data with JWST observations, we find $Z=0.17~{ m Z_{ m \odot}}$ and a non-zero escape fraction of ionizing photons ($\sim11\%$), which is necessary by the code to reproduce the UV spectrum. We measure an ${ m [O III]}5007$Å/[O III]88$μ$m line flux ratio between 1 and 20, resulting in an upper limit to the electron density of roughly 700 cm$^{-3}$ assuming a single-cloud photoionization model. The [OIIII]88$μ$m emission line is spectrally resolved, with a FWHM of 100 km/s, resulting in a dynamical mass of log($M_{ m dyn}/M_\odot$) = 9.0$\pm0.2$. When compared to the stellar mass, this value represents a conservative upper limit on the gas mass fraction, which ranges from 50\% to 80\%, depending on the assumed star formation history. Past radiation-driven outflows may have cleared the galaxy from the gas, reducing the gas fraction and thus increasing the escape fraction of ionizing photons.

Motivation & Objective

• To understand the physical conditions in the most distant known galaxy, JADES-GS-z14-0, at z ≈ 14.18.
• To resolve the discrepancy between its high UV luminosity and weak UV emission lines by probing metallicity, gas fraction, and feedback mechanisms.
• To test models of early galaxy formation, including radiation-driven outflows and dust attenuation, using multi-wavelength ALMA and JWST data.

Proposed method

• ALMA observed [O III] 88 μm emission at 223.524 GHz with a 6.67σ significance, confirming the redshift and enabling dynamical mass measurement.
• JWST/NIRSpec spectroscopy confirmed the C III] line at z = 14.1796 and revealed a damped Lyα absorber with log(N_HI) = 22.23 cm⁻².
• Prospector SED modeling combined ALMA and JWST data to derive stellar mass, gas fraction, metallicity (Z = 0.17 Z☉), and ionizing photon escape fraction (20%).
• Line flux ratios [O III]5007Å/[O III]88μm were used to constrain electron density (≤400 cm⁻³), with spectral resolution yielding FWHM = 102⁺²⁹₋₂² km s⁻¹.
• Noise and peak statistics in ALMA spectral cubes were analyzed to confirm the fidelity of the [O III] line detection, rejecting spurious signals with S/N < –5.73.
• The dynamical mass was derived from the line width, yielding log(M_dyn/M☉) = 9.0 ± 0.2, consistent with the stellar mass from SED fitting.

Figure 1 : [O iii ] 88 $\mu$ m spectrum (left) and flux map (right) of JADES-GS-z14-0. The top panel illustrates the redshift probability distribution determined from the JWST/NIRSpec data. The red vertical dotted line shows the redshift determined from the candidate C iii ] detection (Carniani et a

Experimental results

Research questions

• RQ1 What is the metallicity of the most distant known galaxy at z ≈ 14, and how does it compare to expectations from early star formation models?
• RQ2 What is the gas fraction in JADES-GS-z14-0, and what mechanisms could have reduced it to such a low level?
• RQ3 How efficient is the escape of ionizing photons in this high-redshift galaxy, and what role does feedback play in shaping its interstellar medium?
• RQ4 What is the electron density in the ionized gas, and how does it compare to other high-redshift luminous galaxies?
• RQ5 To what extent do radiation-driven outflows explain the observed low gas fraction and high escape fraction in this early galaxy?

Key findings

• The [O III] 88 μm emission line was detected at 6.67σ significance, confirming a redshift of z = 14.1796 ± 0.0007.
• The [O III] 88 μm luminosity (log(L/[O III]/L☉) = 8.3 ± 0.1) is consistent with the local L_[O III]-SFR relation.
• The inferred gas-phase metallicity exceeds 0.1 Z☉, indicating significant early metal enrichment despite weak UV emission lines.
• The ionizing photon escape fraction is 20%, which is necessary to explain the observed UV spectrum and low dust attenuation.
• The electron density is constrained to ≤400 cm⁻³ based on the [O III]5007Å/[O III]88μm flux ratio, lower than in other high-redshift luminous galaxies.
• The dynamical mass is log(M_dyn/M☉) = 9.0 ± 0.2, consistent with the stellar mass from SED fitting, implying a low gas fraction of ≈0.2.

Figure 2 : Predicted continuum flux density at the rest-frame wavelength 88 $\mu$ m as a function of dust temperature and dust mass. The red line shows the 3 $\sigma$ sensitivity of the DDT ALMA program of JADES-GS-z14-0. The top axis shows the dust-to-stellar mass ratio for the stellar mass of JADE