Physical Characterization of Early Galaxies in the Webb's First Deep Field SMACS J0723.3-7323
This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift $z>7$. By applying a conservative Lyman-break selection followed by photometric redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to $z=7.663$, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at $7<z_{\rm phot}<13$. The NIRCam images clearly resolve all sources and reveal their sub-galactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of $\sim50$ Myr) of sub-solar metallicity ($\sim0.2\,Z_\odot$) and little dust attenuation ($A_{V}\sim0.5$). In several cases, we observe extreme Hb+[OIII] lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies of the same fields (Adams et al., Atek et al., Donnan et al., Harikane et al., Yan et al.), implying the high fidelity of our selection. We cross-match all high-$z$ galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.