The Tip of Red Giant Branch Distances to Nearby Dwarf Galaxies WLM and Sextans A with JWST

Abstract

Distance measurements to extragalactic systems that are both accurate and precise are cornerstones of modern astrophysics, underpinning the calibration of standard candles and the determination of the Hubble constant. Dwarf galaxies, such as Wolf-Lundmark-Melotte (WLM) and Sextans A, provide valuable laboratories for testing distance scales across different stellar populations. In this work, we utilize the high sensitivity and spatial resolution of the James Webb Space Telescope (JWST) to measure the distances to WLM and Sextans A using the tip of the red giant branch (TRGB) method. Adopting the TRGB absolute magnitude calibrated by NGC 4258, we determine distance moduli of $\mu_{\mathrm{0,WLM}} = 24.977 \pm 0.018 (\mathrm{stat}) \pm 0.056 (\mathrm{sys})$ mag for WLM and $\mu_{\mathrm{0,SexA}} = 25.740 \pm 0.011 (\mathrm{stat}) \pm 0.057 (\mathrm{sys})$ mag for Sextans A. Our results are consistent within a 3% distance uncertainty with previous measurements based on TRGB, Cepheids, and J-Region Asymptotic Giant Branch (JAGB) methods. With improved distance measurements in the future, these two galaxies have the potential to serve as additional anchor points for TRGB calibration, aiming to reduce the TRGB-based distance uncertainty to below 2%.