Physically Motivated Stellar Populations for Galaxies at Cosmic Dawn with a Temperature-Dependent IMF
The first few years of James Webb Space Telescope observations have identified previously undetected galaxies at $z>12$ and provided new constraints on galaxies at $z>8$. Many of these objects have stellar masses that are difficult to reconcile with $Λ$CDM, inferred from models not calibrated for the high-redshift Universe. This necessitates new, more astrophysically plausible stellar population models for estimating stellar masses of galaxies at cosmic dawn. We introduce a simple stellar population (SSP) library, Simple Stellar Populations with Temperature (SSPT), computed using a temperature-dependent stellar initial mass function and its implementation in the public code CIGALE. When used in a configuration designed for high-redshift galaxies that requires young stellar population ages, the new models predict stellar masses that are ~0.3-0.5 dex lower than estimates from similar CIGALE analyses using models calibrated to the local Universe, and nearly 2 dex lower than estimates from analyses using other codes and softer constraints on stellar ages. Application of these physically motivated stellar populations suggests that stellar masses of early star-forming galaxies are not in tension with $Λ$CDM, and that galaxy formation from virialized halos remains a reasonable hypothesis at the highest redshifts. The SSPT SSPs and their CIGALE implementation are released publicly.