The TRGB−SBF Project. III. Refining the HST Surface Brightness Fluctuation Distance Scale Calibration with JWST

Abstract The TRGB−SBF Project team is developing an independent distance ladder using a geometrical calibration of the tip of the red giant branch (TRGB) method in elliptical galaxies that can, in turn, be used to set the surface brightness fluctuation (SBF) distance scale independent of Cepheid variables and Type Ia supernovae. The purpose of this project is to measure the local expansion rate of the Universe independently of the methods that are most at odds with the theoretically predicted value of the Hubble–Lemaître constant H 0 , and therefore isolate the influence of potential systematic observational errors. In this paper, we use JWST TRGB distances calibrated using the megamaser galaxy NGC 4258 to determine a new Cepheid-independent SBF zero-point with the Hubble Space Telescope. This new calibration, along with improved optical color measurements from Pan-STARRS and DECam, gives an updated value of H 0 = 73.8 ± 0.7 (statistical) ±2.3 (systematic) km s −1 Mpc −1 that is virtually identical to the SBF Hubble–Lemaître constant measured by J. P. Blakeslee et al.