EDGE-INFERNO: Simulating Every Observable Star in Faint Dwarf Galaxies and Their Consequences for Resolved-star Photometric Surveys

Abstract

Interpretation of data from faint dwarf galaxies is made challenging by observations limited to only the brightest stars. We present a major improvement to tackle this challenge by undertaking zoomed cosmological simulations that resolve the evolution of all individual stars more massive than 0.5 M ⊙ , thereby explicitly tracking all observable stars for the Hubble time. For the first time, we predict observable color–magnitude diagrams and the spatial distribution of ≈100,000 stars within four faint ( M ⋆  ≈ 10 5 M ⊙ ) dwarf galaxies directly from their cosmological initial conditions. In all cases, simulations predict complex light profiles with multiple components, implying that typical observational measures of structural parameters can make the total V -band magnitudes appear up to 0.5 mag dimmer compared to estimates from simulations. Furthermore, when only small (⪅100) numbers of stars are observable, shot noise from realizations of the color–magnitude diagram introduces uncertainties comparable to the population scatter in, e.g., the total magnitude, half-light radius, and mean iron abundance measurements. Estimating these uncertainties with fully self-consistent mass growth, star formation, and chemical enrichment histories paves the way for more robust interpretation of dwarf galaxy data.