Status Report on the Chicago-Carnegie Hubble Program (CCHP): Measurement of the Hubble Constant Using the Hubble and James Webb Space Telescopes

TL;DR

The paper tackles the precision of the local distance scale and H0 by employing JWST to calibrate three independent distance indicators—Cepheids, TRGB, and JAGB—in a sample of 11 SN Ia hosts plus NGC 4258. It presents the JWST observations, data reduction, and analysis framework, including a blinding protocol and anchor calibration, to minimize dust, metallicity, and crowding systematics. The resulting H0 estimates indicate good internal consistency between TRGB and JAGB distances and compatibility with the SH0ES Cepheid calibration, yielding H0 ≈ 70 km s−1 Mpc−1 with subpercent to percent-level uncertainties; the JWST-only TRGB is 68.81 ± 1.79 (stat) ± 1.32 (sys) and JAGB 67.80 ± 2.17 (stat) ± 1.64 (sys). The results are consistent with ΛCDM, and the authors emphasize that future JWST data will further improve precision.

Abstract

We present the latest results from the Chicago-Carnegie Hubble Program (\cchp) to measure the Hubble constant, using data from the James Webb Space Telescope (JWST). The overall program aims to calibrate three independent methods: (1) Tip of the Red Giant Branch (TRGB) stars, (2) JAGB (J-Region Asymptotic Giant Branch) stars, and (3) Cepheids. To date, our program includes 10 nearby galaxies, hosting 11 Type Ia supernovae (SNe Ia) suitable for measuring the Hubble constant ($H_0$). It also includes the galaxy NGC 4258, whose geometric distance provides the zero-point calibration. In this paper we discuss our results from the TRGB and JAGB methods. Our current best (highest precision) estimate is $H_0$ = 70.39 $\pm$ 1.22 (stat) $\pm$ 1.33 (sys) $\pm$ 0.70 ($σ_{SN}$), based on the TRGB method alone, with a total of 24 SN Ia calibrators from both HST and JWST data. Based on our new JWST data only, and tying into SNe Ia, we find values of $H_0$ = 68.81 $\pm$ 1.79 (stat) $\pm$ 1.32 (sys) for the TRGB, and $H_0$ = 67.80 $\pm$ 2.17 (stat) $\pm$ 1.64 (sys) km/s/Mpc for the JAGB method. The distances measured using the TRGB and the JAGB method agree, on average, at a level better than 1%, and with the SH0ES Cepheid distances at just over the 1% level. Our results are consistent with the current standard LambdaCDM model, without the need for the inclusion of additional new physics. Future JWST data will be required to increase the precision and accuracy of the local distance scale.

Figures (4)

• Figure 1: Relative probability densities for $H_{0}$ values from Planck planck_2018, DESI DESI_2024 and the CCHP TRGB measurement from this study. Our current best estimate of $H_{0}$ is 70.39 $\pm$ 1.22 (stat) $\pm$ 1.33 (sys) $\pm$ 0.70 ($\sigma_{SN}$) km s$^{-1}$ Mpc$^{-1}$. The results are all consistent, to within their uncertainties.
• Figure 2: Images of the 11 galaxies observed as part of this program. North is up and east is to the left. The images have been obtained from the following public sources: SDSS: M101 and NGC 4258 ; DECaLS: NGC 1365, 3972, 4038, 4424, 4536, 4639, 7250 ;ESO: NGC 2442 ; and NOIRLab: NGC 5643. The red and white squares denote the footprint of JWST NIRCam and HST WFC3, respectively. The small green squares in M101 and NGC 4258 are ACS WFC.
• Figure 3: Examples of Cepheids in NGC 2442, NGC 3972, NGC 4038, NGC 5643 and NGC 7250 shown in HST filters $F555W, ~F814W$ and $F160W$, as well as the JWST filter $F115W$. These cutouts are made from drizzled images, with pixel scale equal to 0.035” in $F555W, F814W$, and $F115W$, and equal to 0.10” in $F160W$. Thus, for consistency in comparison, these pixel scales are comparable to the average pixel size of the detectors used with each filter. In each cutout image, the maximum pixel value is set to the brightness at the center of the Cepheid point spread function. With this scaling, any white pixel on the cutout images is equal to or greater in brightness than the target Cepheid itself. From this figure, the higher resolution of the near-infrared JWST ($F115W$) images can be seen relative to those of HST ($F160W$). In addition, it can be seen that the optical HST images ($F555W$ and $F814W$) are of higher resolution than the $F160W$ images owing both to the better resolution and less contamination from red giants and asymptotic giant branch stars.
• Figure 4: F115W versus (F115W-F444W) color-magnitude diagram for the galaxy NGC 7250. The positions of all three distance indicators used in our program are identified in the plot. Schematically, the dashed slanted black lines indicate the approximate blue and red edges of the Cepheid instability strip; the white sloped line indicates the position of the TRGB; and the dotted line indicates the peak of the carbon/JAGB stellar luminosity distribution. Red points are stars in the outer field of the galaxy; blue points are stars in the inner field of the galaxy.