First Batch of Candidate Galaxies at Redshifts 11 to 20 Revealed by the James Webb Space Telescope Early Release Observations

Abstract: On July 13, 2022, NASA released to the whole world the data obtained by the James Webb Space Telescope (JWST) Early Release Observations (ERO). These are the first set of science-grade data from this long-awaited facility, marking the beginning of a new era in astronomy. In the study of the early universe, JWST will allow us to push far beyond z ~ 11, the redshift boundary previously imposed by the 1.7 um red cut-off of the Hubble Space Telescope (HST). In contrast, JWST's NIRCam reaches 5 um. Among the JWST ERO targets there is a nearby galaxy cluster SMACS 0723-73, which is a massive cluster and has been long recognized as a potential "cosmic telescope" in amplifying background galaxies. The ERO six-band NIRCam observations on this target have covered an additional flanking field not boosted by gravitational lensing, which also sees far beyond HST. Here we report the result from our search of candidate objects at z > 11 using these ERO data. In total, there are 87 such objects identified by using the standard "dropout" technique. These objects are all detected in multiple bands and therefore cannot be spurious. For most of them, their multi-band colors are inconsistent with known types of contaminants. If the detected dropout signature is interpreted as the expected Lyman-break, it implies that these objects are at z ~ 11--20. The large number of such candidate objects at such high redshifts is not expected from the previously favored predictions and demands further investigations. JWST spectroscopy on such objects will be critical.

• The paper identifies 87 candidate galaxies at redshifts 11 to 20 using the dropout technique with JWST's NIRCam.
• It employs multi-band spectral energy distribution fitting and corroborates findings with Le Phare and EAZY to ensure robust redshift estimates.
• The results challenge previous models of galaxy formation and emphasize the importance of JWST in exploring early cosmic structures.

Analysis of High-Redshift Galaxy Candidates Identified by JWST

The paper presents a study capitalizing on the James Webb Space Telescope's (JWST) Early Release Observations (ERO) to expand upon existing understandings of high-redshift galaxies. The focus is on identifying candidate galaxies in the redshift range of approximately $z \approx 11$ to $20$. The research utilizes data obtained from the observation of the SMACS 0723-73 galaxy cluster, which serves as a cosmic telescope due to its gravitational lensing properties.

Data and Methodology

The research exploits the NIRCam instrument on JWST, which provides longer wavelength capabilities compared to the Hubble Space Telescope (HST), reaching up to $\sim 5 \mu m$ as opposed to the 1.7 $\mu m$ red cutoff of HST. This extension allows for the exploration of galaxies beyond the previously established $z \approx 11$ limit of the HST.

Utilizing the dropout technique, which identifies high-redshift galaxies by their characteristic Lyman-break in their spectral energy distribution (SEDs), the search yielded 87 candidate objects at $z > 11$. The analysis ensured that these detections were not spurious by confirming their presence in multiple bands and comparing colors to known contaminants such as mid-z galaxies and brown dwarfs.

The data analysis involved spectral energy distribution fitting to derive photometric redshifts and other properties using BC03 models. Le Phare and EAZY software were used to corroborate the high-redshift nature of these candidates through probability distribution functions of redshift estimates.

Findings

The outcomes present an unexpectedly large number of high-redshift candidates, which challenges prevailing expectations based on prior theoretical models that predicted a scarcity of galaxies at these redshifts. The $z_{\rm ph}$ median for identified dropouts suggests redshifts as high as $z \approx 16$ for some samples.

The photometric redshift distribution showed 83% of F150W dropouts and most F200W dropouts having primary or secondary solutions at $z > 10$. This abundance asks for a reconsideration of the number density of galaxies during the early universe, particularly between redshifts $z \approx 12$ and $17$.

Implications and Future Work

The findings have significant implications for understanding cosmic reionization and the formation history of early galaxies. They suggest a need for reevaluation of high-redshift galaxy formation models, potentially adjusting the expectations for galaxy assembly and star formation rates in these early epochs.

Additionally, spectroscopic follow-up studies of these candidates are essential to confirm their redshift and glean detailed insights into their characteristics. Such investigations could further refine the framework of high-redshift galaxy evolution and constrain properties of the universe at such early times effectively opening a new field of study thanks to JWST's capabilities.

The research underscores the necessity of leveraging advanced astronomical facilities like JWST to peel back layers of uncertainty surrounding the earliest cosmic structures. This exploration could see substantial theoretical advancement aligned with empirical discoveries as astronomical methodologies continue to evolve.