Measuring distances to low-luminosity galaxies using surface brightness fluctuations

Johnny P. Greco, Pieter van Dokkum, Shany Danieli, Scott G. Carlsten, Charlie Conroy

Published 2020-04-15Version 1

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, and proposed WFIRST filter systems. We compare our calculations to the observed SBF magnitudes of dwarf galaxies that have independent distance measurements from the tip of the red giant branch method. Consistent with previous studies, we find that single-age population models show excellent agreement with the observed SBF-color relation of low-mass galaxies with $0.5 \lesssim g - i \lesssim 0.9$. For bluer galaxies, the observed relation is better fit by models with composite stellar populations. To study SBF recovery from low-luminosity galaxies, we perform detailed image simulations in which we inject fully populated model galaxies into deep ground-based images from real observations. We demonstrate that measurements of SBF magnitudes from these simulated data correspond to the theoretical values with negligible bias ($\lesssim0.01$ mag). We then use the simulations to show that LSST will provide data of sufficient quality and depth to measure SBF distances with precisions of ${\sim}10$-20% to ultra-faint $\left(\mathrm{10^4 \leq M_\star/M_\odot \leq 10^5}\right)$ and low-mass classical ($\leq10^7$ M$_\odot$) dwarf galaxies out to ${\sim}4$ Mpc and ${\sim}25$ Mpc, respectively, within the first few years of its deep-wide-fast survey. Many 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.