Two Remarkably Luminous Galaxy Candidates at $z\approx10-12$ Revealed by JWST

Abstract: The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5\mu$m and covering 49 arcmin$^{2}$ from the public Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt $\gtrsim1.8$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$\alpha$ that is redshifted to $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5\sigma$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.

• The paper identifies two bright Lyman-break galaxies at z≈11 and z≈13 using JWST NIRCam data, marking a major step in high-redshift galaxy discovery.
• It employs detailed photometric redshift fitting and GALFIT morphological analysis to robustly confirm the galaxies’ high redshift and potential disk structure.
• The study highlights JWST's capability to unveil early cosmic structures, paving the way for spectroscopic follow-up that could refine models of early galaxy formation.

Overview of "Two Remarkably Luminous Galaxy Candidates at $z\approx11-13$ Revealed by JWST"

This paper details a photometric study conducted using the James Webb Space Telescope (JWST) to identify and analyze two highly luminous galaxy candidates at redshifts $z \approx 11$ and $z \approx 13$, named GLASS-z11 and GLASS-z13 respectively. These candidates were identified through a sweep of JWST Early Release Science programs targeting extragalactic fields using the NIRCam instrument. This discovery marks a significant advancement in the field: only a single galaxy at such high redshifts had been spectroscopically confirmed prior to this study.

Key Findings

1. Identification of Bright Lyman-Break Galaxies: The two candidates exhibit substantial Lyman breaks of $\gtrsim 2.5$ magnitudes in their spectral energy distributions (SEDs), consistent with their classification as high-redshift galaxies. These breaks denote absorption of flux blueward of Lyman-alpha due to neutral hydrogen in the intergalactic medium.
2. Photometric Redshifts and Stellar Properties: Detailed photometric redshift fitting using EAZY and Prospector codes aligns with $z\approx11$ and $z\approx13$, affirming their identification amidst potential low-redshift interlopers. The stellar masses of these systems are approximated to be around a billion solar masses, built up relatively quickly after the Big Bang.
3. Lack of Lower-Redshift Solutions: The derived photometric redshifts are robust against contamination from dusty low-redshift interlopers, particularly quiescent galaxies with potential Balmer breaks, under JWST's unprecedented sensitivity.
4. Morphological Characteristics: Analysis using GALFIT suggests that GLASS-z11 may even represent an organized disk structure—a remarkable possibility at such formidable cosmic timescales.

Implications

1. Probing Early Galaxy Formation: These galaxies expand the frontier of known luminous sources at cosmic dawn, challenging existing models of galaxy formation. Their properties suggest efficient stellar mass assembly at $z > 10$, implying highly efficient star-formation mechanisms or other astrophysical phenomena that exceed current theoretical predictions.
2. Constraints on UV Luminosity Function: The detection supports a potential departure from simple exponential Schechter function predictions towards a double power-law form at bright-end luminosities for these redshifts, hinting at more complex underlying distributions of galaxies in the early universe.
3. Potential for Spectroscopic Follow-Up: These luminous, early galaxies are prime candidates for JWST’s NIRSpec instrument, which can confirm redshifts through spectroscopic techniques. This could further validate photometric findings and refine characteristics such as metallicity and specific star-formation rates.

Conclusion and Future Directions

This study illustrates JWST's capability to probe faint and distant cosmic objects, extending our understanding of early universe structure formation. Given these significant advancements, future efforts might involve more extensive surveys to refine cosmic assembly timelines and further investigate potential high-efficiency star-formation regions indicated by these findings. The study highlights the importance of JWST in unfolding new astrophysical phenomena at the universe's earliest epochs, promising rich returns for observational cosmology and theories of initial stellar mass gather.