Five Oldest Population III Lb Galaxy Candidates: Population Synthesis Approach

Overview

Population III (Pop III) objects are the first generation of stars in the universe, forged directly from the primordial gas of post-Big-Bang Recombination. Though they have never been directly imaged, their signature is detectable through observation of the He II spectroscopic line, an emission feature produced by strong ionizing sources. Yet the vast majority of Pop III candidates in the Epoch of Reionization (EoR), of which there are few, have been shown to be contaminants or lower-redshift interlopers. Using a novel model-forward broadband-based technique, I present the first ever Lyman-break galaxy (LBG) Pop III candidates in the EoR (Lyα equivalent width ≤ 20). SEDs of z~6 Pop III LBGs and redshift-dependent IGM attenuation models are first simulated and synthetically observed with UltraVISTA and Subaru-HSC broadband filters. Using Bayesian-optimized polynomial splines, color criteria are determined and candidates are filtered from the COSMOS2020 photometric catalog. The sample is extensively assessed for contamination from brown dwarfs, Balmer-break contaminants, and high-z interlopers. In particular, IRAC [3.6]-[4.5] colors are assessed to eliminate any z~6 CR7 counterparts. In total, five COSMOS candidates are discovered with estimated He II equivalent widths (EW) up to 210 Ã..., the highest He II EW observed in the EoR. The comparatively high effectiveness and built-in scalability of this technique can be leveraged in countless IR surveys to probe the first billion years of the universe in search of the first stars.

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