Beasts in the Bubbles: Remarkably UV-bright Galaxies at z=9-10

Subaru/SWIMS | 1.5N | PI - S. Fujimoto

(Awarded back-up instrument time on SWIMS)

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.