EPOCHS I. The Discovery and Star Forming Properties of Galaxies in the Epoch of Reionization at $6.5 < z < 18$ with PEARLS and Public JWST data

Abstract: We present in this paper the discovery, properties, and a catalog of 1165 high redshift $6.5 < z < 18$ galaxies found in deep JWST NIRCam imaging from the GTO PEARLS survey combined with data from JWST public fields. We describe our bespoke homogeneous reduction process and our analysis of these areas including the NEP, CEERS, GLASS, NGDEEP, JADES, and ERO SMACS-0723 fields with over 214 arcmin$^{2}$ imaged to depths of $\sim 30$ mag. We describe our rigorous methods for identifying these galaxies, involving the use of Lyman-break strength, detection significance criteria, visual inspection, and integrated photometric redshifts probability distributions predominately at high redshift. Our sample is a robust and highly pure collection of distant galaxies from which we also remove brown dwarf stars, and calculate completeness and contamination from simulations. We include a summary of the basic properties of these $z > 6.5$ galaxies, including their redshift distributions, UV absolute magnitudes, and star formation rates. Our study of these young galaxies reveals a wide range of stellar population properties as seen in their colors and SED fits which we compare to stellar population models, indicating a range of star formation histories, dust, AGN and/or nebular emission. We find a strong trend exists between stellar mass and $(U-V)$ color, as well as the existence of the `main-sequence' of star formation for galaxies as early as $z \sim 12$. This indicates that stellar mass, or an underlying variable correlating with stellar mass, is driving galaxy formation, in agreement with simulation predictions. We also discover ultra-high redshift candidates at $z > 12$ in our sample and describe their properties. Finally, we note a significant observed excess of galaxies compared to models at $z > 12$, revealing a tension between predictions and our observations.

• The paper identifies 1165 high-redshift galaxies using uniform data reduction and rigorous selection criteria from JWST imaging.
• It reveals a 'main-sequence' where stellar mass correlates with UV color, challenging existing galaxy formation models.
• The findings demonstrate JWST’s capability to probe early universe galaxies and call for refined simulations to explain excess high-redshift detections.

Discovery and Star Formation Properties of High-Redshift Galaxies with JWST

The paper explores the notable advances in understanding galaxy formation during the epoch of reionization, enabled by data from the James Webb Space Telescope (JWST). The study focuses on galaxies in the redshift range $6.5 < z < 18$, utilizing imaging from the JWST NIRCam, as part of the GTO PEARLS survey and other public JWST datasets.

Key Findings and Methodology

The research identifies 1165 high-redshift galaxies using a homogeneous reduction process. This vast sample, derived from a significant sky area of over 214 square arcminutes and depth reaching $\sim 30$ magnitudes, was carefully selected using Lyman-break strength and other rigorous criteria to exclude contaminants like brown dwarfs. The study describes how photometric redshift probability distributions were primarily leveraged for galaxy identification.

The investigation reveals a diverse range of stellar population properties within these young galaxies. This is evidenced by their observed and rest-frame colors, aligning with various stellar population models. A particularly noteworthy result is the existence of a 'main-sequence' of star formation. This sequence implies a trend where stellar mass correlates with UV color, suggesting that despite the complexities of galaxy formation, stellar mass is a crucial driver at these epochs.

Implications and Future Directions

This research has significant implications both theoretically and practically. The presence of the 'main sequence' at redshifts as early as $z \sim 12$ challenges current galaxy formation models and offers insights into early universe conditions. It also highlights potential tension with existing simulations, given the observed excess of galaxies at high redshifts, especially beyond $z > 12$, compared to model predictions. This discrepancy may require revisions of current simulations to account for these dense populations of early galaxies.

From a practical perspective, this work underscores the capability of JWST in revolutionizing our understanding of the early universe. The findings could steer future observational strategies, emphasizing the need for deeper and broader surveys to fully map the high-redshift universe and unravel the mysteries of early galaxy formation.

Conclusion

Overall, this study is a pivotal step in expanding our knowledge of the high-redshift universe. The rigorous identification and analysis of a significant sample of distant galaxies provide foundational data that challenge existing models and highlight the capabilities of JWST. As more JWST observations become available, they promise to further refine our understanding of galaxy evolution in the universe's infancy.