Templates for Fitting Photometry of Ultra-high-redshift Galaxies

Recent data from the James Webb Space Telescope allow a first glimpse of galaxies at z & GSIM; 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 that 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, such that stellar masses are no longer seemingly inconsistent with ?CDM. The two new template sets are released in formats compatible with EAZY and LePhare.

Automated summary

Recent data from the James Webb Space Telescope provide the first glimpse of galaxies at z > 11. Photometric template fitting is used to identify and infer properties of ultra-high-redshift candidates. Two sets of synthetic templates are developed, optimized for the expected astrophysics of galaxies at different redshift ranges, and used to fit three galaxies at z > 12 in the SMACS0723 field. These improved templates help quantify the bias in inferred properties from JWST observations at z > 8.