A Glimpse of the New Redshift Frontier Through Abell S1063 (2411.13640v3)

Abstract: We report the discovery of two galaxy candidates at redshifts between $15.7<z<16.4$ in JWST observations from the GLIMPSE survey. These robust sources were identified using a combination of Lyman-break selection and photometric redshift estimates. The ultra-deep NIRCam imaging from GLIMPSE, combined with the strong gravitational lensing of the Abell S1063 galaxy cluster, allows us to probe an intrinsically fainter population (down to $M_{\rm UV} =-17.0$ mag) than previously achievable. These galaxies have absolute magnitudes ranging from $M_{\rm UV} = -17.0$ to $-17.2$ mag, with blue ($\beta \simeq -2.87$) UV continuum slopes, consistent with young, dust-free stellar populations. The number density of these objects, log${\rm 10}$($\phi$/[Mpc$^{-3}$ mag$^{-1}$])=$-3.47^{+0.13}{-0.10}$ at $M_{\rm UV}=-17$ is in clear tension with pre-JWST theoretical predictions, extending the over-abundance of galaxies from $z\sim10$ to $z\sim 17$. These results, together with the scarcity of brighter galaxies in other public surveys, suggest a steep decline in the bright-end of the UV luminosity function at $z \sim 16$, implying efficient star formation and possibly a close connection to the halo mass function at these redshifts. Testing a variety of star formation histories suggests that these sources are plausible progenitors of the unusually UV-bright galaxies that JWST now routinely uncovers at $z = 10-14$. Overall, our results indicate that the luminosity distribution of the earliest star-forming galaxies could be shifting towards fainter luminosities, implying that future surveys of cosmic dawn will need to explore this faint luminosity regime.

• The paper identifies five high-redshift galaxy candidates using JWST’s NIRCam and the Lyman-break technique amidst strong gravitational lensing.
• The paper applies advanced photometric redshift estimation with EAZY and BEAGLE to validate galaxies down to M_UV = -17.5 mag, overcoming cluster light contamination.
• The paper reveals a discrepancy between observed faint galaxy densities and theoretical predictions, indicating robust early star formation activity.

Overview of "A Glimpse of the New Redshift Frontier Through Abell S1063"

The paper "A Glimpse of the New Redshift Frontier Through Abell S1063" by Kokorev et al. addresses the discovery of galaxy candidates with high redshifts ($15.9$M_{\rm UV}=-17.5$ mag.

Methodology

The authors deployed the ultra-deep imaging capabilities of JWST's Near Infrared Camera (NIRCam) in the GLIMPSE survey, aimed at detecting galaxies from an epoch very close to the cosmic dawn. The gravitational lensing potential of the Abell S1063 cluster serves to amplify the faint signals of distant galaxies, allowing the detection of these high-redshift objects that are inaccessible to previous surveys, even with the Hubble Space Telescope (HST).

The data analysis involves several steps, including:

1. Lyman Break Selection: Selection of candidates involves identifying dropouts in specific filters where the Lyman-alpha break manifests at high redshifts.
2. Photometric Redshift Estimation: Using EAZY and BEAGLE software, photometric redshifts are calculated to confirm the redshifts of potential galaxy candidates and validate the Lyman-break selection.
3. Cluster Light Contamination Removal: Treatment of strong light contamination from the cluster galaxies is essential for accurate photometry.
4. Size and Morphology Analysis: Investigation of the morphology of the galaxies to ensure they are not artifacts or low-redshift interlopers.

Key Findings

1. Abundance and Luminosity Function: The paper reveals a pronounced discrepancy between observed galaxy number densities at these high redshifts and pre-JWST theoretical predictions. The observed number density of faint galaxies suggests a high level of star formation activity early in the Universe's history, extending the tension observed between theory and recent JWST detections.
2. Stellar Population Characteristics: The photometric data suggest these galaxies have properties consistent with early stellar populations, characterized by a UV continuum slope indicative of young, dust-free environments. Star-formation rates calculated from the observed UV magnitudes suggest modest star-forming activities.
3. Lack of Brighter Galaxies at $z>16$: No bright galaxies ($M_{\rm UV}<-19$) were detected at these redshifts, pointing toward a potential steep decline in the bright end of the UV luminosity function.

Implications and Future Directions

The abundance of faint galaxies at $z > 16$ implies efficient star formation possibly linked with a rapid assembly of dark matter halos, challenging simple extrapolations of existing models of star formation during the early Universe. The lack of bright detections suggests a pivot towards understanding the mechanisms enabling such prolific star formation without yielding exceptionally luminous galaxies at these epochs.

This paper's findings provide robust empirical data that constrains galaxy formation models and enhances our understanding of the Universe's formative stages. Future theoretical work must reconcile these observations with star formation models, potentially adjusting the halo mass function or star formation efficiencies. Consequently, upcoming observational campaigns with JWST and advanced simulations are crucial to further explore this new redshift frontier opened by the GLIMPSE survey.