Discovery of Red Galaxy Candidates at; z; ∼ 12: Early Dust Growth or Significant Nebular Emission with High-temperature Stars?
Journal Article
Overview
abstract
Abstract; ; We report the discovery of two; z; ∼ 12 galaxy candidates with unusually red UV slopes (; β; UV; ≳ −1.5), and probe the origin of such colors at cosmic dawn. From; Prospector; fits to the UNCOVER/MegaScience dataset—deep JWST/NIRCam imaging of A2744 in 20 broad- and medium bands—we identify several new; z; > 10 galaxies. Medium-band data improve redshift estimates, revealing two lensed (; μ; ∼ 3.3); z; ∼ 12 galaxies in a close pair with; β; UV; ≳ −1.5 at an UV absolute magnitude of; M; UV; ∼ −19 mag, lying away from typical scatter on previously known; M; UV; –; β; UV; relations. Spectral energy distribution fitting with; Prospector; ,; Bagpipes; , and; EAZY; support their high-; z; nature, with probability of low-; z; interlopers of; p; (; z; < 7) < 10%. The potential low-; z; interlopers are; z; ∼ 3 quiescent galaxies (QGs), but unexpected to be detected at the given field of view unless; z; ∼ 3 QG stellar mass function has a strong turn up at; ; ; ; ; ; log; ; ; M; ; ; *; ; ; [; ; ; M; ; ; ⊙; ; ; ]; ∼; 9; ; ; . Unlike typical blue high-redshift candidates (; β; UV; ≲ −2.0), these red slopes require either dust or nebular continuum reddening. The dust scenario implies; A; ; V; ; ∼ 0.8 mag, which is larger than theoretical predictions, but is consistent with a dust-to-stellar mass ratio (; ; ; ; ; ; log; ; ; M; ; ; dust; ; ; /; ; ; M; ; ; *; ; ; ∼; −; 3; ; ; ). The nebular scenario demands dense gas (; ; ; ; ; ; log; ; ; n; ; ; H; ; ; ; [; ; ; cm; ; ; −; 3; ; ; ]; ∼; 4.0; ; ; ) around hot stars (; ; ; ; ; ; log; ; ; T; ; ; eff; ; ; ; [; K; ]; ∼; 4.9; ; ; ). Spectroscopic follow-up is essential to determine their true nature and reveal missing galaxies at the cosmic dawn.;
