We conduct a comprehensive study on dropout galaxy candidates at z ∼ 9–16 using the first 90 arcmin2 James Webb Space Telescope (JWST) Near Infrared Camera images taken by the early release observations (ERO) and early release science programs. With the JWST simulation images, we find that a number of foreground interlopers are selected with a weak photo-z determination (Δχ 2 > 4). We thus carefully apply a secure photo-z selection criterion (Δχ 2 > 9) and conventional color criteria with confirmations of the ERO Near Infrared Spectrograph spectroscopic redshifts, and obtain a total of 23 dropout galaxies at z ∼ 9–16, including two candidates at z phot = 16.25 − 0.46 + 0.24 and 16.41 − 0.55 + 0.66 . We perform thorough comparisons of dropout galaxies found in our work with recent JWST studies, and conclude that our galaxy sample is reliable enough for statistical analyses. We derive the UV luminosity functions at z ∼ 9–16, and confirm that our UV luminosity functions at z ∼ 9 and 12 agree with those determined by other Hubble Space Telescope and JWST studies. The cosmic star formation rate (SFR) density decreases from z ∼ 9 to 12, and perhaps to 16, but the densities at z ∼ 12–16 are higher than the constant star formation efficiency model. Interestingly, there are six bright galaxy candidates at z ∼ 10–16 with M UV < −19.5 mag and M * ∼ 108−9 M ⊙. Because a majority (∼80%) of these galaxies show no signatures of active galactic nuclei in their morphologies, the high cosmic SFR densities and the existence of these UV-luminous galaxies are explained by the lack of suppression of star formation by the UV background radiation at the pre-reionization epoch and/or an efficient UV radiation production by a top-heavy initial mass function with Population III–like star formation.

We conduct a comprehensive study on dropout galaxy candidates at z ∼ 9 − 17 using the first 90 arcmin 2 JWST/NIRCam images taken by the early release observations (ERO) and early release science (ERS) programs. With the JWST simulation images, we find that a number of foreground interlopers are selected with a weak photo-z determination (∆χ 2 > 4). We thus carefully apply a secure photo-z selection criterion (∆χ 2 > 9) and conventional color criteria with confirmations of the ERO NIRSpec spectroscopic redshifts, and obtain a total of 25 dropout galaxies at z ∼ 9−17, including two candidates at z phot = 16.45 +0.09 −0.32 and 16.66 +1.86 −0.34 . We perform thorough comparisons of dropout galaxies found in our work with recent JWST studies, and conclude that our galaxy sample is reliable enough for statistical analyses. We derive the UV luminosity functions at z ∼ 9 − 17, and confirm that our UV luminosity functions at z ∼ 9 and 12 agree with those determined by previous HST and JWST studies. The cosmic star-formation rate density decreases from z ∼ 9 to 12, and perhaps to 17, but the densities at z ∼ 12 − 17 are higher than the constant star formation efficiency model. Interestingly, there are six bright galaxy candidates at z ∼ 11 − 17 with M UV < −19.5 whose stellar masses are very high, 10 8−9 M . Because a majority (∼ 70%) of these galaxies shows no signatures of AGNs in their morphologies, the high cosmic star-formation rate densities and the existence of these stellar massive galaxies are explained by no suppression of star-formation by the UV background radiation at the pre-reionization epoch or an efficient UV radiation production by Population III-like star formation.

We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (∼500 deg2) optical images reaching a 5σ limit of ∼26 mag, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z ⊙ < 0.1 EMPGs from ∼40 million sources detected in the Subaru images, we first develop a machine-learning (ML) classifier based on a deep neural network algorithm with a training data set consisting of optical photometry of galaxy, star, and QSO models. We test our ML classifier with SDSS objects having spectroscopic metallicity measurements and confirm that our ML classifier accomplishes 86% completeness and 46% purity EMPG classifications with photometric data. Applying our ML classifier to the photometric data of the Subaru sources, as well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG candidates from the Subaru and SDSS photometric data, respectively. We conduct optical follow-up spectroscopy for 10 of our EMPG candidates with Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS and find that the 10 EMPG candidates are star-forming galaxies at z = 0.007–0.03 with large Hβ equivalent widths of 104–265 Å, stellar masses of log( / ) = 5.0–7.1, and high specific star formation rates of ∼300 Gyr−1, which are similar to those of early galaxies at z ≳ 6 reported recently. We spectroscopically confirm that 3 out of 10 candidates are truly EMPGs with Z/Z ⊙ < 0.1, one of which is HSC J1631+4426, the most metal-poor galaxy, with Z/Z ⊙ = 0.016, ever reported.

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