Recent data from the James Webb Space Telescope allow a first glimpse of galaxies at z≳11. The most successful tool for identifying ultra-high-redshift candidates and inferring their properties is photometric template fitting. However, current methods rely on templates derived from much lower-redshift conditions, including stellar populations older than the age of the Universe at z>12, a stellar initial mass function which is physically disallowed at z>6, and weaker emission lines than currently observed at z>7.5. Here, two sets of synthetic templates, optimized for the expected astrophysics of galaxies at 8<z<12 and z>12, are developed and used to fit three galaxies at z>12 from the SMACS0723 field. Using these improved templates, quantitative estimates are produced of the bias in inferred properties from JWST observations at z>8 due to these effects. The best-fit redshifts are similar to those found with previous template sets, but the inferred stellar masses drop by as much as 1--1.6 dex, so that stellar masses are no longer seemingly inconsistent with ΛCDM. The two new template sets are released in formats compatible with EAZY and LePhare.
@article{arxiv.2208.07879,
title = {Templates for Fitting Photometry of Ultra-High-Redshift Galaxies},
author = {Charles L. Steinhardt and Vasily Kokorev and Vadim Rusakov and Ethan Garcia and Albert Sneppen},
journal= {arXiv preprint arXiv:2208.07879},
year = {2023}
}