Measuring Distances to Low-luminosity Galaxies Using Surface Brightness Fluctuations

We present an in-depth study of surface brightness fluctuations (SBFs) in low-luminosity stellar systems. Using the MIST models, we compute theoretical predictions for absolute SBF magnitudes in the LSST, HST ACS/WFC, and proposed Roman Space Telescope filter systems. We compare our calculations to observed SBF-color relations of systems that span a wide range of age and metallicity. Consistent with previous studies, we find that single-age population models show excellent agreement with observations of low-mass galaxies with 0.5 less than or similar to g - i less than or similar to 0.9. For bluer galaxies, the observed relation is better fit by models with composite stellar populations. To study SBF recovery from low-luminosity systems, we perform detailed image simulations in which we inject fully populated model galaxies into deep ground-based images from real observations. Our simulations show that LSST will provide data of sufficient quality and depth to measure SBF magnitudes with precisions of similar to 0.2-0.5 mag in ultra-faint (10(4) <= M-star/M-circle dot <= 10(5)) and low-mass classical (M-star <= 10(7) M) dwarf galaxies out to similar to 4 Mpc and similar to 25 Mpc, respectively, within the first few years of its deep-wide-fast survey. Many significant practical challenges and systematic uncertainties remain, including an irreducible sampling scatter in the SBFs of ultra-faint dwarfs due to their undersampled stellar mass functions. We nonetheless conclude that SBFs in the new generation of wide-field imaging surveys have the potential to play a critical role in the efficient confirmation and characterization of dwarf galaxies in the nearby universe.

Automated summary

The study finds that single-age population models provide good agreement with observations of low-mass galaxies, while models with composite stellar populations are better suited for bluer galaxies. LSST is capable of measuring SBF magnitudes with high precision in ultra-faint and low-mass dwarf galaxies within the first few years of its deep-wide-fast survey.