James Webb Space Telescope Feed Post

The Population II Extragalactic Distance Scale: A TRGB Distance to the Fornax Cluster with JWST

Color images of the B4 and A1 chips from our NGC 1380 observations, generated from ???090???/???150???/???356??? imaging. The elongated spatial coverage of NIRCam allows us to capture a large dynamic range of surface brightnesses within a single visit, facilitating simultaneous measurements of Surface Brightness Fluctuations and the Tip of the Red Giant Branch. Abstract: Differences between the local value of the Hubble constant measured via the distance ladder versus the value inferred from the cosmic microwave background with the assumption of the standard ?CDM model have reached over 5s significance. To determine if this discrepancy is due to new physics or more mundane systematic errors, it is essential to remove as many sources of systematic uncertainty as possible by developing high-precision distance ladders that are independent of the traditional Cepheid and Type Ia supernovae route. Here we present JWST observations of three early-type Fornax Cluster galaxies, the first of fourteen observations from a Cycle 2 JWST program. Our modest integration times allow us to measure highly precise tip of the red giant branch (TRGB) distances, and will also be used to perform measurements of Surface Brightness Fluctuations (SBF). From these three galaxies, we determine an average TRGB distance modulus to the Fornax Cluster of µ = 31.424 ± 0.077 mag, or D = 19.3 ± 0.7 Mpc. With eleven more scheduled observations in nearby elliptical galaxies, our program will allow us set the zero point of the SBF scale to better than 2% for more distant measurements, charting a path towards a high-precision measurement of H0 that is independent of the traditional Cepheid-SN Ia distance ladder.