Revealing Galaxy Candidates out to $z \sim 16$ with JWST Observations of the Lensing Cluster SMACS0723 (2207.12338v2)

Abstract: One of the main goals of the JWST is to study the first galaxies in the Universe. We present a systematic photometric analysis of very distant galaxies in the first JWST deep field towards the massive lensing cluster SMACS0723. As a result, we report the discovery of two galaxy candidates at $z\sim16$, only $250$ million years after the Big Bang. We also identify two candidates at $z\sim 12$ and 6 candidates at $z\sim 9-11$. Our search extended out to $z\lesssim21$ by combining color information across seven NIRCam and NIRISS filters. By modelling the Spectral Energy Distributions (SEDs) with \texttt{EAZY} and \texttt{BEAGLE}, we test the robustness of the photometric redshift estimates. While their intrinsic (un-lensed) luminosity is typical of the characteristic luminosity L$^*$ at $z>10$, our high-redshift galaxies typically show small sizes and their morphologies are consistent with disks in some cases. The highest-redshift candidates have extremely blue UV-continuum slopes $-3 < \beta <-2.4$, young ages $\sim 10-100$\,Myr, and stellar masses around $\log(M_{\star}/\mathrm{M}_{\odot})=8.8$ inferred from their SED modeling, which indicate a rapid build-up of their stellar mass. Our search clearly demonstrates the capabilities of JWST to uncover robust photometric candidates up to very high redshifts, and peer into the formation epoch of the first galaxies.

• The paper presents a breakthrough photometric identification of high-redshift galaxy candidates up to z ∼16 using gravitational lensing from SMACS0723.
• It employs JWST data across NIRCam and NIRISS filters with robust SED modeling to validate photometric redshift estimates.
• Its findings challenge conventional galaxy formation models by revealing nascent, disk-like structures in the early universe.

Analysis of High-Redshift Galaxy Candidates Identified by JWST

The paper "Revealing Galaxy Candidates out to $z \sim 16$ with JWST Observations of the Lensing Cluster SMACS0723" presents a detailed photometric paper aimed at understanding the early universe through the detection of high-redshift galaxies. Utilizing the James Webb Space Telescope (JWST), the paper probes into one of the primary objectives of modern astrophysics: uncovering the formation epochs of the first galaxies.

Methodology and Findings

The researchers utilized the JWST observations, specifically focusing on the SMACS0723 lensing cluster, to perform a photometric analysis across seven filters provided by the NIRCam and NIRISS instruments. The gravitational lensing effect of the cluster is instrumental in magnifying distant galaxies, thus enabling the paper to identify very faint and high-redshift galaxies that would otherwise be inaccessible.

Key results of the analysis include:

• Identification of two galaxy candidates at a potentially significant redshift of approximately $z \sim 16$, suggesting formation just 250 million years post-Big Bang.
• Discovery of two further candidates at $z \sim 12$ and six additional candidates in the range $z \sim 9-11$.
• The use of robust photometric redshift estimates validated through Spectral Energy Distributions (SEDs) modeling with the EAZY and BEAGLE tools.
• The candidate galaxies typically exhibit blue UV-continuum slopes ($-3 < \beta <-2.4$), indicative of nascent stars and low dust, and suggest a rapid stellar mass buildup characterized by ages of $10 - 100$ Myr and stellar masses around $\log(M_{\star}/\mathrm{M}_{\odot})=8.8$.

Implications

The discovery of such high-redshift galaxies reinforces JWST's capability to extend the horizon of observable universe epochs and provides a fresh perspective on galaxy formation models. The findings of small, disk-like morphologies in potentially primordial galaxies challenge existing theoretical models, which often predict more irregular and chaotic structures due to turbulent conditions in the early universe.

The photometric technique implemented demonstrates efficacy in distinguishing high-redshift objects via their dropout effect and validates the robustness of methodologies combining lensing magnifications with SED modeling. The results offer notable implications for theoretical models, particularly regarding the UV luminosity function and its redshift evolution. These early galaxy formations could prompt revisions in the modeled timeline for cosmic reionization and the roles early galaxies played therein.

Future Directions

The paper underlines impending prospects for advancing our understanding of high-redshift galaxy formation, warning that further spectroscopic analyses will be necessary to corroborate photometric redshifts and dissect the properties of these early galactic structures more precisely. Such follow-up studies are essential for refining our comprehension of the cosmic dawn and evolution scenarios of the early universe.

Furthermore, the exploration of lensing fields promises to yield invaluable insights into the faint end of the luminosity function, potentially uncovering the true nature and frequency of primordial galaxies. In this regard, future proposals for deep-field JWST observations should emphasize multi-wavelength analyses coupled with advanced lensing models to enhance the robustness of inferred galaxy properties.

By enabling the analysis of previously inaccessible cosmic periods, this research signifies a critical step in piecing together the narrative of cosmic genesis and the embryonic stages of galaxy development. The paper calls for continued astrometric and spectral refinements in high-redshift galaxy studies, encouraging synergy between observational advancements and theoretical frameworks.