Discovery and properties of ultra-high redshift galaxies ($9<z<12$) in the JWST ERO SMACS 0723 Field (2207.11217v3)

Abstract: We present a reduction and analysis of the \textit{James Webb Space Telescope} (JWST) SMACS~0723 field using new post-launch calibrations to conduct a search for ultra-high-redshift galaxies ($z > 9$) present within the Epoch of Reionisation. We conduct this search by modelling photometric redshifts in several ways for all sources and by applying conservative magnitude cuts ($m_{\rm F200W} < 28$) to identify strong Lyman breaks greater than 1 magnitude. We find four $z > 9$ candidate galaxies which have not previously been identified, with one object at $z = 11.5$, and another which is possibly a close pair of galaxies. We measure redshifts for candidate galaxies from other studies and find the recovery rate to be only 23 per cent, with many being assigned lower redshift, dusty solutions in our work. Most of our $z > 9$ sample show evidence for Balmer-breaks, or extreme emission lines from H$\beta$ and [OIII], demonstrating that the stellar populations could be advanced in age or very young depending on the cause of the F444W excess. We discuss the resolved structures of these early galaxies and find that the S\'{e}rsic indices reveal a mixture of light concentration levels, but that the sizes of all our systems are exceptionally small ($< 0.5$~kpc). These systems have stellar masses M${*} \sim 10^{9.0}$ M${\odot}$, with our $z \sim 11.5$ candidate a dwarf galaxy with a stellar mass M${*} \sim 10^{7.8}$ -- $10^{8.2}$ M${\odot}$. These candidate ultra high-redshift galaxies are excellent targets for future NIRSpec observations aimed to better understand their physical nature.

• The paper identifies four new galaxy candidates at z>9 using robust photometric redshift modeling and strict magnitude cuts.
• The study reveals very compact structures (radii <0.5 kpc) with disk-like light profiles, characteristic of early dense galaxies.
• The analysis cross-verifies observations with theoretical models, emphasizing discrepancies and the need for spectroscopic confirmations.

Overview of Ultra-High Redshift Galaxies in the JWST SMACS 0723 Field

The paper entitled "Discovery and properties of ultra-high redshift galaxies ($9

Objectives and Methodology

The research aims to push the boundaries of known redshifts by examining data from the SMACS 0723 field to discover galaxies at redshifts greater than 9. The paper employs both photometric redshift modeling and stringent magnitude cuts to ensure the robustness of the identified high-redshift candidates. The methodology involves a detailed photometric analysis using the Near Infrared Camera (NIRCam) from JWST, along with post-launch calibrations and advanced data processing techniques tailored to the high precision demands of high-redshift galaxy identification.

Key Findings

1. Identification of High-Redshift Candidates:
   • The paper identifies four new galaxy candidates at $z > 9$, including a galaxy estimated to be at $z = 11.5$. These candidates are characterized by features indicative of both Lyman-breaks and Balmer-breaks or high-equivalent-width emission lines, providing insights into their stellar populations.
2. Photometric and Structural Characteristics:
   • The galaxies exhibit very compact structures with effective radii mostly under 0.5 kpc, affirming the notion of smaller, denser galaxies during this early epoch. The morphological analysis suggests disk-like light profiles prevalent among these high-redshift galaxies.
3. Comparative Analysis with Previous Data:
   • A critical aspect of the research involves cross-verifying identified candidates with those reported in other studies. This analysis highlights discrepancies and stresses the need for consistency in data reduction and photometric redshift calculation methodologies.
4. Stellar Mass Estimations:
   • The stellar masses inferred range from $\sim 10^7.8$ M$_{\odot}$ to $10^{9.0}$ M$_{\odot}$, with the highest redshift candidate being categorized as a dwarf galaxy. This mass range is consistent with expectations for early Universe galaxies, avoiding conflicts with cosmological models.
5. Theoretical Implications:
   • The paper compares observational findings with predictions from several theoretical models, including semi-analytic and hydrodynamical simulations. While some agreement is noted in terms of number densities, distinct variations highlight the need for larger samples and further studies to refine theoretical frameworks.

Implications and Future Directions

The findings presented contribute significantly to the burgeoning field of extragalactic astronomy facilitated by JWST's capabilities. By identifying and characterizing galaxies at such high redshifts, the paper provides critical data points for models of early galaxy formation and the reionization timeline.

Future efforts will likely focus on obtaining spectroscopic confirmations of these high-redshift candidates to further elucidate their physical properties. Moreover, as data processing techniques evolve and the depth of observations increases, it is expected that the catalog of known high-redshift galaxies will expand, offering richer insights into the Universe's formative epochs.

The methodological rigor and analytical depth of this paper set a benchmark for future explorations in high-redshift astronomy, contributing to a more nuanced understanding of the earliest stages of galactic evolution and cosmic history.