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Arxiv: JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0 Published: 8/21/2024 7:47:09 PM Updated: 10/28/2024 7:53:52 PM

Paper abstract: JWST provides new opportunities to cross-check the HST Cepheid/SNeIa distanceladder, which yields the most precise local measure of H0. We analyze earlyJWST subsamples (~1/4 of the HST sample) from the SH0ES and CCHP groups,calibrated by a single anchor (N4258). We find HST Cepheid distances agree well(~1 sigma) with all 8 combinations of methods, samples, and telescopes: JWSTCepheids, TRGB, and JAGB by either group, plus HST TRGB and Miras. Thecomparisons explicitly include the measurement uncertainty of each method inN4258, an oft-neglected but dominant term. Mean differences are ~0.03 mag, farsmaller than the 0.18 mag "Hubble tension." Combining all measures produces thestrongest constraint yet on the linearity of HST Cepheid distances,0.994+-0.010, ruling out distance-dependent bias or offset as the source of thetension at ~7 sigma. Yet, measurements of H0 from current JWST subsamplesproduce large sampling differences whose size and direction we can directlyestimate from the full HST set. We show that Delta(H0)~2.5 km/s/Mpc between theCCHP JWST program and the full HST sample is entirely consistent withdifferences in sample selection. Combining all JWST samples produces a new,distance-limited set of 16 SNeIa at D<25 Mpc and more closely resembles thefull sample thanks to "reversion to the mean" of larger samples. Using JWSTCepheids, JAGB, and TRGB, we find 73.4+-2.1, 72.2+-2.2, and 72.1+-2.2 km/s/Mpc,respectively. Explicitly accounting for SNe in common, the combined-samplethree-method result from JWST is H0=72.6+-2.0, similar to H0=72.8 expected fromHST Cepheids in the same galaxies. The small JWST sample trivially lowers theHubble tension significance due to small-sample statistics and is not yetcompetitive with the HST set (42 SNeIa and 4 anchors), which yields 73.2+-0.9.Still, the joint JWST sample provides important crosschecks which the HST datapasses.