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

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.

• The paper confirms four metal-poor galaxies at z=10.3–13.2 using deep NIRSpec observations with JWST.
• It employs a rigorous methodology that combines NIRCam detections with NIRSpec spectroscopy to identify the Lyman continuum break for precise redshift determination.
• Findings reveal low stellar masses and modest star formation rates, offering key insights into early chemical enrichment and the reionization era.

Spectroscopic Confirmation of Four Metal-Poor Galaxies at z=10.3-13.2

The research presented in the paper capitalizes on the capabilities of the James Webb Space Telescope (JWST), specifically employing its NIRSpec instrument, to substantiate the existence of four metal-poor galaxies at redshifts 10.3 to 13.2. This spectroscopic confirmation extends humanity's observational reach deeper into cosmic dawn, a critical period in cosmic history encompassing the first billion years after the Big Bang.

Methodology and Observational Strategy

The paper details rigorous spectroscopic observations conducted as part of the JWST Advanced Deep Extragalactic Survey (JADES). Using the near-infrared capabilities of JWST's NIRCam for initial detection, candidate galaxies were identified based on a lack of flux in specific bands, suggesting high redshifts. Subsequently, NIRSpec's configurable microshutters facilitated deep-spectrum acquisition, achieving a sensitivity of 28.4 magnitudes (AB) at 5σ per resolution element at 2.5 μm. The configuration primarily involved NIRSpec's prism setup, advantageous for its targeted resolution and sensitivity across the required spectral range.

This approach allowed spectroscopic validation of high-redshift targets previously reliant on photometric redshift estimates subject to contamination by low-redshift interlopers. The depth and quality of spectra acquired were unprecedented, with exposure times ranging from 9.3 to 28 hours, allowing accurate determination of redshift through spectral features such as the Lyman continuum break.

Key Findings

The spectroscopic analysis presented a robust detection of four galaxies at redshifts exceeding 10, demonstrating young ages and low metallicities, estimated to be only a few percent of solar. This suggests they are amongst the earliest galaxies to form, likely seeded by the first generation of stars. The identified galaxies show low stellar masses (around 10^9 solar masses), with modest star formation rates of a few solar masses per year.

Importantly, these observations imposed constraints on the neutral hydrogen fraction in the intergalactic medium, through examination of the damping wings at the Lyman edge. The spectral breaks observed are consistent with a largely neutral IGM at these early cosmic epochs, indicating these galaxies are situated prior to or during the reionization period.

The dominance of continuum emission with weak line features in the spectra supports a scenario with significant ionizing photon escape, potentially contributing to reionization.

Implications

The confirmation of these galaxies provides crucial insights into galaxy formation and evolution models, offering empirical data against which theoretical predictions can be tested. The presence of metal-poor galaxies at such significant redshifts underscores the efficiency of early star formation and subsequent chemical enrichment.

The lack of strong emission lines challenges current models of early galaxy emission-line properties, prompting a reevaluation of the ionization and metallicity processes occurring in these nascent systems. This study also highlights the necessity of spectroscopic follow-up to photometric surveys for accurate high-redshift galaxy characterization.

Future Prospects

This work extends the cosmological frontier probed by JWST, foreshadowing continued investigations into the early universe. Upcoming spectroscopic investigations with JWST will likely refine our understanding of the earliest epochs of star formation, the progression of reionization, and the evolution of galaxy metallicity and stellar populations.

As JWST continues to collect data, the understanding of cosmic dawn will become increasingly detailed, bridging gaps in knowledge about the formation and evolution of the earliest galaxies. This ongoing research will continue to shed light on the initial conditions that influenced the development of the large-scale structures we observe in the universe today.