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We cross-check the Hubble Space Telescope (HST) Cepheid/Type Ia supernova (SN Ia) distance ladder, which yields the most precise local H _0 , against early James Webb Space Telescope (JWST) subsamples (∼1/4 of the HST sample) from SH0ES and CCHP, calibrated only with NGC 4258. We find HST Cepheid distances agree well (∼1 σ ) with all combinations of methods, samples, and telescopes. The comparisons explicitly include the measurement uncertainty of each method in NGC 4258, an oft-neglected but dominant term. Mean differences are ∼0.03 mag, far smaller than the 0.18 mag “Hubble tension.” Combining all measures produces the strongest constraint yet on the linearity of HST Cepheid distances, 0.994 ±0.010, ruling out distance-dependent bias or offset as the source of the tension at ∼7 σ . However, current JWST subsamples produce large sampling differences in H _0 whose size and direction we can directly estimate from the full HST set. We show that Δ H _0 ∼ 2.5 km s ^−1 Mpc ^−1 between the CCHP JWST program and the full HST sample is entirely consistent with differences in sample selection. We combine all JWST samples into a new distance-limited set of 16 SNe Ia at D ≤ 25 Mpc. Using JWST Cepheids, JAGB, and tip of the red giant branch, we find 73.4 ± 2.1, 72.2 ± 2.2, and 72.1 ± 2.2 km s ^−1 Mpc ^−1 , respectively. Explicitly accounting for common supernovae, the three-method JWST result is H _0 = 72.6 ± 2.0, similar to H _0 = 72.8 expected from HST Cepheids in the same galaxies. The small JWST sample trivially lowers the Hubble tension significance due to small-sample statistics and is not yet competitive with the HST set (42 SNe Ia and 4 anchors), which yields 73.2 ± 0.9. Still, the joint JWST sample provides important cross-checks that the HST data pass.

The Hubble Tension, a >5 σ discrepancy between direct and indirect measurements of the Hubble constant ( H _0 ), has persisted for a decade and motivated intense scrutiny of the paths used to infer H _0 . Comparing independently derived distances for a set of galaxies with different standard candles, such as the tip of the red giant branch (TRGB) and Cepheid variables, can test for systematics in the middle rung of the distance ladder. The I band is the preferred filter for measuring the TRGB due to constancy with color, a result of low sensitivity to population differences in age and metallicity supported by stellar models. We use James Webb Space Telescope (JWST) observations with the maser host NGC 4258 as our geometric anchor to measure I -band (F090W versus F090W − F150W) TRGB distances to eight hosts of 10 Type Ia supernovae (SNe Ia) within 28 Mpc: NGC 1448, NGC 1559, NGC 2525, NGC 3370, NGC 3447, NGC 5584, NGC 5643, and NGC 5861. We compare these with Hubble Space Telescope (HST) Cepheid-based relative distance moduli for the same galaxies and anchor. We find no evidence of a difference between their weighted means, 0.01 ± 0.04 (stat) ± 0.04 (sys) mag. We produce 14 variants of the TRGB analysis, altering the smoothing level and color range used to measure the tips to explore their impact. For some hosts, this changes the identification of the strongest peak, but this causes little change to the sample mean difference, producing a full range of 0.00–0.02 mag, all consistent at 1 σ with no difference. The result matches past comparisons of I -band TRGB and Cepheids when both use HST. SNe and anchor samples observed with JWST are too small to yield a measure of H _0 that is competitive with the HST sample of 42 SNe Ia and 4 anchors; however, they already provide a vital systematic cross-check to HST measurements of the distance ladder.

We study stars in the J-regions of the asymptotic giant branch (JAGB) of near-infrared color–magnitude diagrams in the maser host NGC 4258 and four hosts of six Type Ia supernovae (SNe Ia): NGC 1448, NGC 1559, NGC 5584, and NGC 5643. These clumps of stars are readily apparent near 1.0 < F150W − F277W < 1.5 and m _F150W = 22–25 mag with James Webb Space Telescope NIRCam photometry. Various methods have been proposed to assign an apparent reference magnitude to this recently proposed standard candle, including the mode, median, sigma-clipped mean, or a modeled luminosity function parameter. We test the consistency of these by measuring intrahost variations, finding differences of up to ∼0.2 mag that significantly exceed statistical uncertainties. Brightness differences appear intrinsic, and are further amplified by the nonuniform shape of the JAGB luminosity function, also apparent in the LMC and SMC. We follow a “many methods” approach to measure consistently JAGB magnitudes and distance moduli to the SN Ia host sample calibrated by NGC 4258. We find broad agreement with distance moduli measured from Cepheids, tip of the red giant branch, and Miras. However, the SN host mean distance modulus estimated via the JAGB method necessary to estimate H _0 differs by ∼0.19 mag among the above definitions, the result of different levels of luminosity function asymmetry. The methods yield a full range of 71−78 km s ^−1 Mpc ^−1 , i.e., a fiducial result of H _0 = 74.7 ± 2.1(stat) ± 2.3(sys, ±3.1 if combined in quadrature) km s ^−1 Mpc ^−1 , with systematic errors limited by the differences in methods. Future work may seek to standardize and refine this promising tool further, making it more competitive with established distance indicators.

The tip of the red giant branch (TRGB) allows for the measurement of precise and accurate distances to nearby galaxies based on the brightest ascent of low-mass red giant branch stars before they undergo the helium flash. With the advent of JWST, there is great promise to utilize the technique to measure galaxy distances out to at least 50 Mpc, significantly further than the Hubble Space Telescope's (HST's) reach of 20 Mpc. However, with any standard candle, it is first necessary to provide an absolute reference. Here, we use Cycle 1 data to provide an absolute calibration in the F090W filter. F090W is most similar to the F814W filter commonly used for TRGB measurements with HST, which had been adopted by the community due to its minimal dependence on the underlying metallicities and ages of stars. The imaging we use was taken in the outskirts of NGC 4258, which has a direct geometrical distance measurement from the Keplerian motion of its water megamaser. Utilizing several measurement techniques, we find ${M}_{\mathrm{TRGB}}^{{\rm{F}}090{\rm{W}}}$ = −4.362 ± 0.033 (stat) ± 0.045 (sys) mag (Vega) for the metal-poor TRGB. We also perform measurements of the TRGB in two Type Ia supernova hosts, NGC 1559 and NGC 5584. We find good agreement between our TRGB distances and previous determinations of distances to these galaxies from Cepheids (Δ = 0.01 ± 0.06 mag), with these differences being too small to explain the Hubble tension (∼0.17 mag). In addition, we showcase the serendipitous discovery of a faint dwarf galaxy near NGC 5584.

We present phase-corrected photometric measurements of 88 Cepheid variables in the core of the Small Magellanic Cloud (SMC), the first sample obtained with the Hubble Space Telescope's (HST) Wide Field Camera 3, in the same homogeneous photometric system as past measurements of all Cepheids on the SH0ES distance ladder. We limit the sample to the inner core and model the geometry to reduce errors in prior studies due to the nontrivial depth of this cloud. Without crowding present in ground-based studies, we obtain an unprecedentedly low dispersion of 0.102 mag for a period–luminosity ( P – L ) relation in the SMC, approaching the width of the Cepheid instability strip. The new geometric distance to 15 late-type detached eclipsing binaries in the SMC offers a rare opportunity to improve the foundation of the distance ladder, increasing the number of calibrating galaxies from three to four. With the SMC as the only anchor, we find H _0 = 74.1 ± 2.1 km s ^−1 Mpc ^−1 . Combining these four geometric distances with our HST photometry of SMC Cepheids, we obtain H _0 = 73.17 ± 0.86 km s ^−1 Mpc ^−1 . By including the SMC in the distance ladder, we also double the range where the metallicity ([Fe/H]) dependence of the Cepheid P – L relation can be calibrated, and we find γ = −0.234 ± 0.052 mag dex ^−1 . Our local measurement of H _0 based on Cepheids and Type Ia supernovae shows a 5.8 σ tension with the value inferred from the cosmic microwave background assuming a Lambda cold dark matter (ΛCDM) cosmology, reinforcing the possibility of physics beyond ΛCDM.

We present a low-dispersion period–luminosity relation (PL) based on 154 Cepheids in Messier 33 (M33) with Hubble Space Telescope (HST) photometry from the PHATTER survey. Using high-quality ground-based light curves, we recover Cepheid phases and amplitudes for multi-epoch HST data and we perform template fitting to derive intensity-averaged mean magnitudes. HST observations in the SH0ES near-infrared Wesenheit system significantly reduce the effect of crowding relative to ground-based data, as seen in the final PL scatter of σ = 0.11 mag. We adopt the absolute calibration of the PL based on HST observations in the Large Magellanic Cloud and a distance derived using late-type detached eclipsing binaries to obtain a distance modulus for M33 of μ = 24.622 ± 0.030 mag ( d = 840 ± 11 kpc), a best-to-date precision of 1.3%. We find very good agreement with past Cepheid-based measurements. Several tip of the red giant branch estimates bracket our result while disagreeing with each other. Finally, we show that the flux contribution from star clusters hosting Cepheids in M33 does not impact the distance measurement and we find only ∼3.7% of the sample is located in (or nearby) young clusters. M33 offers one of the best sites for the cross-calibration of many primary distance indicators. Thus, a precise independent geometric determination of its distance would provide a valuable new anchor to measure the Hubble constant.