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We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 < z < 9 galaxies with spectroscopic redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with Bagpipes, using six NIRCam imaging bands spanning the wavelength range 0.8–5 μm. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of [O iii]+Hβ reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.

We present the results of a systematic search for candidate quiescent galaxies in the distant universe in 11 JWST fields with publicly available observations collected during the first 3 months of operations and covering an effective sky area of ∼145 arcmin2. We homogeneously reduce the new JWST data and combine them with existing observations from the Hubble Space Telescope. We select a robust sample of ∼80 candidate quiescent and quenching galaxies at 3 < z < 5 using two methods: (1) based on their rest-frame UVJ colors, and (2) a novel quantitative approach based on Gaussian mixture modeling of the near-UV − U, U − V, and V − J rest-frame color space, which is more sensitive to recently quenched objects. We measure comoving number densities of massive (M ⋆ ≥ 1010.6 M ⊙) quiescent galaxies consistent with previous estimates relying on ground-based observations, after homogenizing the results in the literature with our mass and redshift intervals. However, we find significant field-to-field variations of the number densities up to a factor of 2–3, highlighting the effect of cosmic variance and suggesting the presence of overdensities of red quiescent galaxies at z > 3, as could be expected for highly clustered massive systems. Importantly, JWST enables the robust identification of quenching/quiescent galaxy candidates at lower masses and higher redshifts than before, challenging standard formation scenarios. All data products, including the literature compilation, are made publicly available.

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