JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H 0

2.1.1. Previous HST Samples

The full HST Cepheid sample from SH0ES (R22) is a distance-limited (z ≤ 0.01) set of 42 SNe Ia in 37 late-type hosts (since 2021) calibrated by four different anchors. This sample provides an ideal reference for all other samples because it contains all of the subsamples described here. In Table A1, we present a compilation of relevant information for the full HST sample of SN Ia hosts and selected JWST subsamples, similar to Table 6 of R22 but with NGC 4258 as the sole anchor, ¹³ allowing for a direct comparison with other methods or telescopes that rely only on this galaxy. We also make use of HST I-band TRGB measurements in SN Ia hosts given by W. L. Freedman (2021) calibrated to NGC 4258 and Miras measured in SN Ia hosts calibrated to NGC 4258 (C. D. Huang et al. 2024).

2.1.2. JWST Observations

To briefly review, we can measure the distance modulus to an SN Ia host by measuring the magnitude (m) or dereddened magnitude (m⁰) of a type of standard candle, a or b, in the ith host and also in NGC 4258. From these, we obtain their difference in distance modulus and then add the known geometric (maser) distance modulus, μ_0,N4258:

with

where

Note that these equations assume that all error terms are independent and uncorrelated. We note that an individual host magnitude uncertainty, σ(m_i,a ) is defined to include both measurement error and intrinsic scatter of the candle. Equation (4) provides the error in the difference in distance moduli for a single host or for a sample of hosts by substituting σ_a and σ_b from Equation (5).

The difference in distance modulus between the methods, Δμ(a − b), is independent of knowledge of the geometric distance, μ_0,N4258. For a sample of N SN Ia hosts, the uncertainty in the measured differences, , will be reduced by (Equation (5)), but uncertainties from the independent measurements of two methods in NGC 4258, , become the limiting factors for measuring the difference. We see no way to avoid this term as it encompasses the quality of the measurements in NGC 4258, which could vary from excellent to poor, which would be reflected in this term. For a population-based indicator like TRGB or JAGB, this term would also include any intrinsic field-to-field (or population-to-population) scatter. F24 (Table 5) refers to measurement uncertainties in NGC 4258 together with the 1.5% geometric distance uncertainty from M. J. Reid et al. (2019) as a systematic uncertainty in H₀, terms which total 2.2%–4.3% for each method.

An (external) systematic error for each method, sys_a and sys_b , may describe a relative uncertainty between NGC 4258 and the SN hosts and may (be hoped to) partially cancel if it applies equally to methods a and b (or may have a covariance term to include). The uncertainty in the two-method comparison thus contains three basic terms: the error in the host subsample mean measurements, the uncertainties in each method’s measurements made in NGC 4258, and any relevant (external) systematic error that applies between them. These terms apply separately to both telescopes or methods and thus affect their comparison.

We give illustrative but realistic error budgets for the methods and comparisons in Table 1. For each method, we derive the statistical uncertainties from the measurements in the first and second rungs for an assumption of one anchor (NGC 4258) and ∼10 SN hosts. We also give a systematic uncertainty due to differences between the SN host and NGC 4258 applicable for that method.

Table 1. Representative Error Budget for Comparing Two JWST Distance Method Samples (∼10 Hosts Calibrated to NGC 4258)

Term	σ(stat)	σ(sys)
	(mag)
Cepheids
Method calibration measurement: intercept in NGC 4258 (∼100 Cepheids)	0.03	⋯
SN host sample means: intercepts,	0.02	⋯
Systematic between SN hosts and NGC 4258, P–L slope: (slope), othera	⋯	0.01–0.05
Cepheid Subtotal	0.04	0.03
TRGB
Method calibration measurement: TRGB mag in NGC 4258	0.04	⋯
SN host sample means: ∼0.06	0.02	⋯
Systematic between SN hosts and NGC 4258, intrinsic TRGB variationb	⋯	0.01–0.08
TRGB Subtotal	0.045	0.01–0.08
JAGB
Method calibration measurement: JAGB mag in NGC 4258	0.05	⋯
SN host sample means: ∼0.06	0.02	⋯
Systematic between SN hosts and NGC 4258, intrinsic JAGB Methodc	⋯	0.01–0.10
JAGB Subtotal	0.055	0.01–0.10
Comparison between the two methodsd	0.06	∼0.03–0.10
Total	0.07–0.12

Notes. An uncertainty budget for the present analysis. Uncertainties are listed separately for each distance method (Cepheids, TRGB, and JAGB), and their individual subtotals are given.

^a A mean difference in log P between NGC 4258 and an SN Ia host of ∼0.3 times a slope uncertainty of ∼0.05; “other” leaves room for other choices, but R24 shows a range of <0.03 mag for a wide range of choices. ^b Term highly dependent on the bands and colors used to measure; the low end would be suitable for I band, where TRGB is least sensitive to metallicity and age, and the high end of the range for NIR. ^c Level of differences for different measures, e.g., mode versus mean versus median of JAGB LF. ^d Depends on (a) and (b), which also will impact the weights; optimistic case here.

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For a realistic measurement error per host for Cepheids, TRGB, or JAGB of 0.05–0.08 mag, 10 hosts will yield an error in the mean (Equation (5)) of 0.02–0.03 mag. A critical and often-neglected term in a two-method comparison is the measurement error for NGC 4258 (Cepheid P–L intercept or TRGB/JAGB apparent magnitude) for each telescope and method, which does not cancel in the comparison in the way the geometric distance error does. Ideally, NGC 4258 would be the best-measured object, but in practice, this may not occur. For the quality of Cepheid measurements from JWST presented in R24, the uncertainty in the intercept of NGC 4258 using ∼100 Cepheids is 0.02 mag though it appears greater for the CCHP observations (F24, Table 5). For TRGB, we take the measurement error from F24 of 0.035 mag (see Appendix B for further discussion). For JAGB, we take this uncertainty to be 0.05 mag from F24 (Table 5) and reported by L24.

The primary (external) systematic difference in the case of Cepheids derives from the difference in period distribution, together with the uncertainty in the slope of the assumed P–L relation. ¹⁵ Metallicity effects largely cancel out, as NGC 4258 and the SN Ia host subsample have very similar measured metallicities; we adopt a common metallicity term of 0.2 mag dex⁻¹, accurate to ∼0.02 mag after application. For a subsample of ∼10 hosts, random uncertainties will depend on the specific targets selected, including the number of Cepheids in each target and the number of epochs observed, which, in turn, impact the P–L scatter; individual uncertainties vary by a factor of a few from target to target. The systematic difference for TRGB is due to intrinsic TRGB variation between the SN hosts and NGC 4258. This is discussed at length by D. Scolnic et al. (2022), J. Wu et al. (2023), and R. I. Anderson et al. (2024) and will be different for TRGB measured in the optical or NIR. We give a range of 0.01–0.08 mag. For JAGB, the range of 0.01–0.10 mag is given owing to the nature of choices in the analysis. As discussed by S. Li et al. (2024b), there are variations up to the 0.1 mag level when applying different statistical techniques (e.g., mode/median).

We find the statistical error from a comparison is likely to be ∼0.06 mag but can range from 0.03 to 0.10 mag for the JWST sample, and the systematic contribution is 0.03–0.1 mag. For each technique, the uncertainty of the measurement for each method in NGC 4258 is the dominant source.

F24 gives uncertainties in two-method comparisons which are a factor of ∼3 smaller than those we derive from their data following standard error propagation (Equation (4) and Table 1). We discuss this further in the Appendix B, where we trace the origin to the nonpropagation of the given measurement uncertainties (or any uncertainty) in the measurements of each distance indicator in NGC 4258.

We show in Figure 2 and Table 2 a comparison of distance measurements using HST Cepheid observations from R22 and those from other HST and JWST observations/techniques. We use the uncertainties as derived in Table 1 for the comparisons. We find that all techniques are in good accord at the ∼1σ and an average level of ∼0.03 mag.

When comparing Cepheid measurements from JWST and HST, we see that the mean difference with the CCHP JWST Cepheid sample of 10 hosts is −0.027 ± 0.10 mag, in the sense of JWST being closer. We note that the CCHP measurements are obtained in F115W, a different filter than used with HST, so systematic error cancellation does not apply, which is part of the reason for the relatively large error. See Figure 1 of A. G. Riess et al. (2023b) for sources of P–L dispersion. When we compare to the Cepheid measurements of the eight SH0ES-selected hosts of 11 SNe Ia, we find a mean difference with the HST Cepheids of −0.02 ±0.03 mag. The uncertainty here is smaller owing to 1) Cepheid samples in the SH0ES hosts which are a factor of ∼3 larger, 2) a P–L scatter which is 40% smaller due to the availability of multiple epochs and colors and 3) the matching of wavelength between JWST and HST (and hence the P–L slope). The JWST and HST Cepheid comparisons presented by A. G. Riess et al. (2024) included 15 variants (i.e., choices) including no period limits, P > 15 day limits, steeper and shallower P–L slope, no or double metallicity correction, most crowded and least crowded halves, no phase correction or single random phase, and the use of Cepheid colors (for dereddening) from HST or from JWST NIR or JWST mid-IR. The mean differences ranged from −0.030 to 0.017 mag, with the fluctuations all less than 1σ. We conclude that HST and JWST Cepheid measurements are robustly consistent (which is also true of the individual team samples).

For comparisons between JWST JAGB and HST Cepheids, we measure a difference with the CCHP JWST sample of 0.047 ± 0.066 mag, and for the SH0ES JWST sample we measure a difference of −0.015 ± 0.064 mag, though this can vary between 0.02 and −0.04, depending on whether the JAGB mode, median, or mean statistic is used, which remains an arbitrary choice (S. Li et al. 2024b). L24 finds that if they apply the mean or median instead of the mode, the JAGB distances would decrease (due to the greater skew of NGC 4258); the agreement would then be 0.01 ± 0.055 mag. F24 noted a larger difference of 0.08 mag between Cepheids and JAGB, but the Cepheid reference was their JWST Cepheids, not the HST Cepheids compared here. As discussed in Appendix B, with the measurement errors in NGC 4258 included, even the JWST-to-JWST difference is only 1σ. The CCHP JWST JAGB−Cepheid difference also matches the size and direction of the difference between CCHP JAGB and CCHP HST TRGB in common, 0.07 mag.

When we compare HST Cepheid distances to TRGB, we measure differences of 0.032, 0.02, and 0.01 mag for JWST CCHP, JWST SH0ES, and HST CCHP, respectively, each with a total uncertainty of ∼0.05−0.06 mag. The JWST I-TRGB measurements are presented by S. Li et al. (2024a) and here limited to the six hosts of eight SNe Ia with D ≤ 25 Mpc. All of these comparisons are in good accord at the ∼1σ level.

2.3.1. Cepheid Distance Linearity

The measurement of H₀ from JWST host subsamples alone will show relatively large variations due to the small number of SNe they contain, coupled to the substantial SN Ia intrinsic scatter. The selection differences and their impacts are illustrated in Figure 4, where we show the difference in H₀ we would expect based on the full sample of host HST Cepheid measurements in R22 and the variation introduced by the anchor. These differences due to selection are often referred to as “subsample bias” because they measure how the subsample represents the full sample. The driver of this variation is the inherent scatter in the luminosity of individual SN Ia, ¹⁶ which is a factor of 2–3 times larger than the uncertainty in the distance estimate to a typical host. For example, the 10 SNe Ia calibrated with JWST in the CCHP sample and analyzed with the Carnegie Supernova Program (CSP) data, where the intrinsic SN Ia dispersion is found to be 0.19 mag (S. A. Uddin et al. 2023), produce a 1σ uncertainty in H₀ of 2.0 km s⁻¹ Mpc⁻¹.

Another difference in H₀ between a JWST-only measurement and the full HST samples results from the availability of anchors. NGC 4258, the sole anchor available for JWST, produces the lowest value of H₀ of the four anchors, decreasing H₀ from the four-anchor mean of L. Breuval et al. (2024) by ΔH₀ ≈ 0.7 km s⁻¹ Mpc⁻¹.

Determining H₀ requires the standardized apparent magnitudes of the SN Ia () in the relevant hosts and absolute magnitudes () determined as . For a well-measured mean , H₀ may be determined from

This is a useful approximation to the empirical calibration for the Pantheon+ SNe Ia sample from R22 (this simplified approximation rather than the full, simultaneous distance-ladder fit including covariance is accurate to ∼0.01 mag). Calibrating all 42 SNe Ia with HST Cepheids and the single anchor, NGC 4258, produces a mean M_B = −19.28 mag and H₀ = 72.5 ± 1.5 km s⁻¹ Mpc⁻¹, matching fit #10 given by R22.

We now predict differences in H₀ due only to the selection of a JWST subsample by comparing the subsample means determined from the HST Cepheid distances using Equation (6). In Table A1, we list the relevant quantities for the full sample of 42 SNe Ia from R22 as well as the SN Ia host subsamples selected for JWST studies. The comparisons between expected (HST) and actual (JWST) measures of H₀ are shown in Figure 5.

For the 10 hosts of 11 SNe Ia selected by the CCHP for JWST observations, HST Cepheids gave mag (where the uncertainty includes the measurement of NGC 4258, ±0.04 without it) and a corresponding value of H₀ = 71.2 km s⁻¹ Mpc⁻¹, thus 2.0 km s⁻¹ Mpc⁻¹ lower than the full HST sample—simply due to the choice of SN hosts and anchor.

An even larger sample difference is expected for the smaller subsample of seven SN Ia hosts for which the CCHP JWST JAGB measurements are provided (L24). A priori, HST Cepheid measurements (see Table 1) find M_B = −19.34 ± 0.05 mag and H₀ = 70.3 km s⁻¹ Mpc⁻¹ for this JAGB subset, an expected reduction of 3.0 km s⁻¹ Mpc⁻¹ from the full HST sample due to selection. The use of CSP instead of the Pantheon+ SN samples reduces this by another 0.7 km s⁻¹ Mpc⁻¹ according to L24, and the selection of the mode statistic rather than the mean or median reduces H₀ by another 1.1 km s⁻¹ Mpc⁻¹. The CCHP JAGB analysis excludes three SN Ia hosts (NGC 3972, 4038, and 4424) from the CCHP sample of 10, and these three excluded objects have a higher expected average, H₀ = 75 km s⁻¹ Mpc⁻¹, based on their HST Cepheid measurements; among the three excluded objects are the two with the highest H₀ from the CCHP sample (NGC 3972 and 4038).

The subsample chosen for the CCHP JAGB measurements produces an unusual combination of draws from the full HST sample, being both low in H₀ and in a very tight cluster, each a ∼2σ level fluctuation. The SN Ia dispersion in M_B of the set is uncommonly low at 0.06 mag, less than half the typical SN Ia population dispersion (D. Brout et al. 2022; D. Scolnic et al. 2022). As shown in Figure 6, only ∼5% of randomly selected samples of eight SNe Ia from the 42 yield an HST Cepheid predicted value of H₀ this low, and ∼5% of samples have SNe with such a small variation in luminosity. These subsample characteristics seen from HST Cepheid measurements are well matched in the actual JWST JAGB measurements (L24). Because the subsample is unusual a priori, a standard uncertainty propagated to H₀ will not account for the uncommonly high difference between this subsample and the full sample mean. This illustrates the greater value of comparing distance measures with one method to distance measures with another for subsamples rather than comparing H₀ or SN scatter, which avoids the issue of uncommon or unrepresentative subsamples.

The value of H₀ found by F24, which is lower than that of R22, is anticipated by the difference of the selected subsample relative to the HST full sample mean and the exclusion of three galaxies for JAGB measurements (see Figure 2, vertical blue line). F24 reports JWST Cepheids in the CCHP-selected sample give a value of ∼72 km s⁻¹ Mpc⁻¹ and NIR-TRGB ∼70 km s⁻¹ Mpc⁻¹, both near the HST-expected ∼71 km s⁻¹ Mpc⁻¹ for the subsample, and JWST JAGB gives ∼69 km s⁻¹ Mpc⁻¹, near the HST measured for that subsample (with three excluded) of 70.3 km s⁻¹ Mpc⁻¹; see Figure 6, all with the Pantheon+ SN sample. For the combination of these three methods, F24 reports 70 km s⁻¹ Mpc⁻¹, near the HST-expected value of ∼70.8 ± 2.3 km s⁻¹ Mpc⁻¹. In summary, the difference of this selected SN subsample relative to the mean and the exclusion of several hosts for JAGB measurements reduce H₀ as expected by the full sample. In Figure 4, we show the individual SN Ia values of H₀ for the full HST sample and the differences from anchor choice as a full summary.

For the SH0ES JWST host selection of 11 SNe Ia in eight hosts, HST Cepheids predict mag and H₀ = 73.9 ± 2.3 km s⁻¹ Mpc⁻¹ (or −19.26 mag and 73.6 km s⁻¹ Mpc⁻¹ for nine SNe Ia with D ≤ 25 Mpc). This represents a ∼1σ fluctuation due to the SN selection in the other direction (a higher H₀). This compares well with the JWST Cepheid measurement of H₀ = 74.2 km s⁻¹ Mpc⁻¹.

The full error bars in Figure 5 include the noise from the small subsample of SN measurements. Thus, for a new measurement with JWST in comparison to HST, the differential errors as given in Table 2 can range from 0.03 to 0.10 mag or from 1 to 3 km s⁻¹ Mpc⁻¹.

To avoid a selection bias relative to the SN Ia population, it is important to define a (combined) sample that is complete to some distance (a common method to avoid magnitude bias and also to avoid the vagaries of human selection). We note that a near-complete sample of SNe Ia (in R22) to D ≤ 25 Mpc with JWST observations is formed by combining both the above SH0ES and CCHP samples for a total of 14 (unique) hosts of 16 SNe Ia, missing only SN 1998aq (NGC 3982) D ≤ 25 Mpc, which neither team targeted. A combined D ≤ 25 Mpc JWST sample excludes one host of two SNe Ia, NGC 5468 from the SH0ES JWST sample, which is at D = 40 Mpc. The CCHP sample of 10 alone does not include hosts of six SNe Ia at distances ≤ 25 Mpc or at distances nearer than that sample's most distant (NGC 4639, μ ≤ 32.0 at 95% confidence): SN 2005df, SN 2007af, SN 2001el, SN 2012ht, SN 2021pit, and SN 1998aq. The merged JWST D ≤ 25 Mpc sample of 16 SNe Ia is also seen to be more representative of the full HST sample of 42 SNe Ia than either group’s selected subsample, an expected consequence of “reversion to the mean” as the samples grow. HST Cepheids predict H₀ = 72.9 ± 2.1 km s⁻¹ Mpc⁻¹ for the JWST D ≤ 25 Mpc sample.

For the merged D ≤ 25 Mpc sample of 16 SNe Ia, we find from JWST Cepheids H₀ = 73.4 ± 2.0 km s⁻¹ Mpc⁻¹, similar to the HST result from this same sample. The joint sample of JWST JAGB and TRGB measurements yield H₀ = 72.2 ± 2.3 km s⁻¹ Mpc⁻¹ and H₀ = 72.1 ± 2.3 km s⁻¹ Mpc⁻¹, respectively. The HST Cepheid expectation for the JAGB H₀ is somewhat smaller at 72.4 km s⁻¹ Mpc⁻¹ due to the exclusion of several hosts in L24. Finally, we can combine all three methods, which yields H₀ = 72.6 ± 2.0 km s⁻¹ Mpc⁻¹, in good agreement with the value expected from HST Cepheids for the same sample of H₀ = 72.8 ± 2.0 km s⁻¹ Mpc⁻¹. The uncertainties for this combination are explained in Table 3 and values of H₀ and their uncertainties for different sub-samples are in Table 4. For these estimates we used the minimum systematic error listed in Table 1 for each method. For an expanded JWST sample of SN Ia hosts with smaller statistical uncertainty, we would advocate a more comprehensive analysis of systematic uncertainties. When we compare the HST predicted values of H₀ to those found with JWST measurements, we find the values inferred using JWST are consistent with expectations for every subsample. We can see that the measured values are at or within 1σ of these smaller uncertainties, i.e., between HST and JWST excluding SNe, for each comparison set. We reiterate that the HST expectations above all come from the use of NGC 4258 as a single anchor, yielding lower values of H₀ by 0.5 than the three anchor calibrations in R22.

Table 3.  H₀ Error Budget for ∼10 SNe Ia Measured with JWST by Three Methods Calibrated by NGC 4258

Term	σ(stat)	σ(sys)
	(mag)
Cepheid subtotal (see Table 1)	0.04	0.03
TRGB subtotal (see Table 1)	0.045	0.01–0.08
JAGB subtotal (see Table 1)	0.055	0.01–0.10
Combining three methods	0.02	∼0.02
Common uncertainties, independent of distance method
First rung: geometric distance to NGC 4258	⋯	0.032
Second rung: SN distances to hosts,a (0.13–0.17)	0.043–0.056	⋯
Third rung: SNe Ia in Hubble flow	⋯	0.01
Common uncertainty subtotal	0.047–0.059	0.04
Cepheids and common total	0.068–0.075	0.044
TRGB and common total	0.065–0.072	0.044
JAGB and common total	0.065–0.072	0.044
Three methods and common total	0.052–0.063	0.044
Three-method stat+sys error in H0: 0.062–0.072 mag or 2.0–2.3 km s−1 Mpc−1;
Individual methods ∼2.5 km s−1 Mpc−1

Note. An uncertainty budget for the present analysis. Uncertainties are listed separately for each distance method (Cepheids, TRGB, and JAGB), and their individual subtotals are given. We derive the uncertainties when combining the three which we label “Three methods.” A separate list of uncertainties, which are common to each distance method (e.g., the uncertainties from SN measurements), are also given. Finally, we combine the averaged uncertainty with the common uncertainty to derive a total H₀ uncertainty. ​​​​​

^a Pantheon + SN sample D. Brout et al. (2022) has a mean per SN Ia error of 0.13 mag; CSP SN sample (S. A. Uddin et al. 2023) finds σ_int = 0.17 per SN for CSP I and II.

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For the merged sample, the averaging of distance methods occurs before the use of SN data to avoid double counting. ¹⁷ It is interesting to examine the much larger sample of all SN Ia hosts observed to date with JWST, which includes 24 of the 42 HST SNe Ia. The full SN sample with JWST observations (to date) is highly representative of the HST SN sample as shown in Figure 6 in terms of expected H₀ and variance with little sample bias. When increasing the number of SN hosts, we can see from the widths of the middle panels in Figure 6 how the second-rung uncertainty from SNe will decrease. The impact of selection when comparing HST and JWST will diminish with the growing samples.

Table A1. Mean SN Ia Derived from Subsamples Calibrated by HST Cepheids, NGC 4258, and Pantheon+ (R22)

Host	μCeph	σ	SN		σ		σ	H0	σ
	(mag)	(mag)		(mag)	(mag)			(km s−1 Mpc−1)
N4258	29.398	0.025 a	⋯	⋯	⋯	⋯	⋯	⋯	⋯
CCHP JWST-selected Targets, N = 11
N7250	31.642	0.130	2013dy	12.283	0.178	−19.357	0.222
N4536	30.870	0.061	1981B	11.551	0.133	−19.320	0.147
N3972 b	31.644	0.096	2011by	12.548	0.094	−19.103	0.136
N4424 b	30.854	0.133	2012cg	11.487	0.192	−19.376	0.236
N4639	31.823	0.091	1990N	12.454	0.124	−19.373	0.155
N4038 b	31.612	0.121	2007 sr	12.409	0.106	−19.212	0.164
M101	29.188	0.055	2011fe	9.7800	0.115	−19.421	0.127
N2442	31.459	0.073	2015F	12.234	0.082	−19.230	0.111
N1365	31.378	0.061	2012fr	11.900	0.092	−19.478	0.112
N5643	30.553	0.063	2013aa	11.252	0.079	−19.322	0.101
N5643	30.553	0.063	2017cbv	11.208	0.074	−19.366	0.097
Mean						−19.32	0.05	71.2	2.0
For JAGB (N = 8): Mean						−19.34	0.05	70.3	2.0
SH0ES JWST-selected/System Targets, N = 11
N1559	31.500	0.071	2005df	12.141	0.086	−19.367	0.112
N1448	31.298	0.051	2001el	12.254	0.136	−19.046	0.146
N1448	31.298	0.051	2021pit	11.752	0.200	−19.548	0.207
N5584	31.766	0.062	2007af	12.804	0.079	−18.963	0.102
N5643	30.553	0.063	2013aa	11.252	0.079	−19.322	0.101
N5643	30.553	0.063	2017cbv	11.208	0.074	−19.366	0.097
N5468	33.127	0.082	1999cp	13.880	0.080	−19.248	0.116
N5468	33.127	0.082	2002cr	13.993	0.072	−19.135	0.111
N4038 b	31.612	0.121	2007 sr	12.409	0.106	−19.212	0.164
N3447	31.947	0.049	2012ht	12.736	0.089	−19.213	0.102
M101 c	29.188	0.055	2011fe	9.7800	0.115	−19.421	0.127
Mean						−19.25	0.05	73.9	2.0
Mean all JWST D ≤ 25 Mpc, 16 SNe Ia						−19.27	0.04	72.8	1.8
SH0ES JWST Cycle 2 Observed
N2525	32.059	0.105	2018gv	12.728	0.074	−19.344	0.130
N3370	32.132	0.062	1994ae	12.937	0.082	−19.196	0.104
N5861	32.232	0.105	2017erp	12.945	0.107	−19.294	0.152
N3147	33.173	0.163	2021hpr	13.843	0.159	−19.358	0.230
N3147	33.173	0.163	1997bq	13.821	0.141	−19.380	0.218
N3147	33.173	0.163	2008fv	13.936	0.200	−19.264	0.260
Mean of all JWST observed, 24 SNe Ia						−19.26	0.03	73.1	1.6
Remaining HST Subsample
N3021	32.473	0.162	1995al	13.114	0.116	−19.368	0.203
N1309	32.552	0.069	2002fk	13.209	0.082	−19.345	0.108
N3982	31.736	0.080	1998aq	12.252	0.078	−19.484	0.113
N1015	32.691	0.077	2009ig	13.350	0.094	−19.346	0.123
N5917	32.377	0.125	2005cf	13.079	0.095	−19.297	0.160
U9391	32.861	0.075	2003du	13.525	0.084	−19.335	0.114
N3583	32.814	0.087	ASASSN-15so	13.509	0.093	−19.308	0.129
N2608	32.620	0.158	2001bg	13.443	0.166	−19.191	0.232
N7541	32.512	0.124	1998dh	13.418	0.128	−19.095	0.181
N0691	32.838	0.114	2005W	13.602	0.139	−19.250	0.182
N3254	32.343	0.084	2019np	13.201	0.074	−19.141	0.114
N5728	33.101	0.208	2009Y	13.514	0.115	−19.607	0.242
N7678	33.196	0.157	2002dp	14.090	0.093	−19.113	0.187
M1337	33.060	0.121	2006D	13.655	0.106	−19.406	0.164
N4680	32.609	0.208	1997bp	13.173	0.205	−19.440	0.296
N7329	33.252	0.122	2006bh	14.030	0.079	−19.248	0.146
N0976	33.719	0.153	1999dq	14.250	0.103	−19.475	0.188
N0105	34.538	0.252	2007A	15.250	0.133	−19.290	0.292
Mean of all unique 42 SNe Ia						−19.28	0.03	72.5	1.5

Note.

^a Includes intercept uncertainty from Cepheid sample and tie to NGC 4258 sample with different mean period; see Table 3. ^b Hosts excluded by CCHP JAGB analysis. ^c JWST program GO-2581. ^d JWST program GO-4087. Sample errors in mean include measurement errors for NGC 4258 but not geometric distance error of 0.032 mag. H₀ follows from with Pantheon+ SNe as 5 log(H .

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Table A2. Distance Moduli for Comparison

Note.

^a The HST TRGB distances given in F21 for NGC 1309, 3021, 3370, and 5584, all at the far end of the measurable range, are contentious as G. S. Anand et al. (2022) have reanalyzed them and could not detect the TRGB. We include them here to keep the F21 sample complete. ^b R24 Table 3 refit R22 HST Cepheids to a common P–L slope with JWST at the same wavelength to negate common error. These HST distance-modulus values (mag) improve the Cepheid comparison with JWST and are N5643, 30.518 ±0.033; N5584, 31.828 ±0.037; N1559, 31.473 ±0.045; N1448, 31.236 ±0.034; and N5468, 33.058 ±0.052. ^c N2525 qualifies for the D < 25 Mpc TRGB sample based on its distance. The uncertainties for the CCHP JWST measures in NGC 4258 were derived from Table 5 in F24 after removing the 1.5% geometric distance uncertainty.

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Table B1. Reducible and Irreducible H₀ Uncertainties from F24

Notes.

^a Error from 10 SNe Ia with intrinsic scatter 0.19 mag from Table 3 in F24 and error in Hubble flow SNe; host distance measures were removed from the random error in F24 Table 5 and put in Column (3). ^b Errors in each method measurement in NGC 4258 after removing the geometric distance error now placed in Column (5). ^c As per F24: NGC 4258 uncertainty in color term, TRGB fitting, extinction, photometry calibration. ^d Uncertainty of 1.5% in NGC 4258 distance (M. J. Reid et al. 2019). ^e As per F24: NGC 4258 uncertainty in the mode, smoothing parameter, convergence error, extinction. ^f As per F24: uncertainty in NGC 4258 reddening law fit zero-point, NGC 4258 P-L cutoff, aperture correction uncertainty, including cross matching the HST catalogs, photometric zero-point uncertainty, and metallicity. ^g Cepheid, TRGB, and JAGB combined errors; first and last columns do not reduce because they use the same SNe and NGC 4258 geometric distance. ^h Or 2.3 km s⁻¹ Mpc⁻¹.

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Table B2. CCHP Distance Method Comparisons without and with Method Measurement Errors in NGC 4258

Note.

^a We note some numerical differences between the weighted mean error given in F24 and what we calculate from their data in Table 2. Most significant is JAGB versus Cepheids, where F24 gives 0.028, and we find 0.040, which reduces the significance of the claimed difference from 3σ claimed by F24 to 2σ and then 0.8σ including the measurement errors for each method in NGC 4258 in Table A1 here and Table 5 in F24.

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