S21B0108

We propose Keck MOSFIRE J-band spectroscopy for five UV-bright (H=24.5–25.4 mag) novel photometric candidates at z=9−10 from the brand new COSMOS2020 catalogs, now benefitting from homogeneous near-IR and ultra-deep optical coverage that allowed for such identification. All candidates have clear Lyman-break features from Y to H bands, IRAC detection, tight distributions in PDF(z) at z=9−10, the inconsistency with the templates of the stellar and dusty galaxy at lower redshift, and are confirmed at z>9 with four independent redshift estimates. The volume density of these five candidates is also consistent with the bright-end of the latest UV luminosity function (UVLF) studies at z=9−10. With the proposed observations, we will achieve the following two major goals: 1) confirming the redshift and the power-law nature of the UVLF at z=9−10, and 2) testing if UV-bright galaxies at z=9−10 host AGN via the Nv1243 line. Importantly, our targets are >× 10–20 brighter than the only other source confirmed at z=9.11. Our targets will provide essential constraints on the bright/massive-end of luminosity/mass function at z>9 and the CDM scenario for the formation of early galaxies, once at least one of their redshifts are confirmed.

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