The Chicago-Carnegie Hubble Program: The JWST J-region Asymptotic Giant Branch (JAGB) Extragalactic Distance Scale (2408.03474v3)

Abstract: The J-region asymptotic giant branch (JAGB) method is a new standard candle based on the constant luminosities of carbon-rich asymptotic giant branch stars in the J band. The JAGB method is independent of the Cepheid and TRGB distance indicators. Therefore, we can leverage it to both cross-check Cepheid and TRGB distances for systematic errors and use it to measure an independent local Hubble constant. The JAGB method also boasts a number of advantages in measuring distances relative to the TRGB and Cepheids, several of which are especially amplified when combined with JWST's revolutionary resolving power. First, JAGB stars are 1 mag brighter in the NIR than the TRGB, and can be discovered from single-epoch NIR photometry unlike Cepheids which require congruent optical imaging in at least 12 epochs. Thus, JAGB stars can be used to measure significantly farther distances than both the TRGB stars and Cepheids using the same amount of observing time. Further advantages include: JAGB stars are easily identified solely via their colors and magnitudes, dust extinction is reduced in near-infrared observations, and JAGB stars are ubiquitous in all galaxies with intermediate-age populations. In this paper, we present a novel algorithm that identifies the optimal location in a galaxy for applying the JAGB method, so as to minimize effects from crowding. We then deploy this algorithm in JWST NIRCam imaging of seven SN Ia host galaxies to measure their JAGB distances, undertaking a completely blind analysis. The zero-point of this JAGB distance scale is set in the water mega-maser galaxy NGC 4258. In our CCHP overview paper Freedman et al. (2025), we apply the JAGB distances measured in this paper to the Carnegie Supernova Program (CSP) SNe Ia sample, measuring a Hubble constant of H0 = 67.80 +/- 2.17 (stat) +/- 1.64 (sys) km/s/Mpc.

• The paper presents a novel calibration technique using carbon-rich JAGB stars to measure extragalactic distances with JWST data.
• It employs NIRCam imaging and a blind analysis to set the distance scale against benchmarks like NGC 4258, yielding H0 = 67.96 km/s/Mpc.
• The findings challenge traditional Cepheid estimates, offering an independent route to resolving discrepancies in local Hubble constant measurements.

An Expert Overview of "The Chicago-Carnegie Hubble Program: The JWST J-region Asymptotic Giant Branch (JAGB) Extragalactic Distance Scale" by Lee et al.

The paper by Lee et al. presents a paper in the field of observational cosmology, focusing on the J-region Asymptotic Giant Branch (JAGB) method as a novel approach for calibrating extragalactic distance scales using the James Webb Space Telescope (JWST). This work is part of the Chicago-Carnegie Hubble Program (CCHP), aiming to measure an independent local Hubble constant ($H_0$), a crucial parameter in cosmology representing the Universe's expansion rate.

Methodological Contributions

The authors introduce an innovative calibration technique using carbon-rich asymptotic giant branch (AGB) stars, specifically emphasizing their standardized luminosities in the J-band. A notable aspect of the JAGB method is its independence from the traditional Cepheid and Tip of the Red Giant Branch (TRGB) distance indicators, offering a potential check against systematic errors inherent to these classical methods. This paper leverages the JWST's advanced resolving power to enhance the precision and accuracy of distance measurements using the JAGB method.

The paper highlights several advantages of using the JAGB stars, including their ubiquity in galaxies with intermediate-age populations, their brightness compared to TRGB stars, and ease of identification using near-infrared photometry. The authors utilize NIRCam imaging data from the JWST, applying a novel algorithm that optimally determines galaxy regions for employing the JAGB method, effectively minimizing impacts from stellar crowding.

Key Findings and Results

The authors conducted a blind analysis using NIRCam imaging of seven type Ia supernovae host galaxies. They set the zero-point for the JAGB distance scale utilizing the well-studied water megamaser galaxy NGC 4258. Employing the resulting distance scale to calibrate supernovae data from the Carnegie Supernova Program (CSP) yielded a measured Hubble constant of $$H_0=67.96 \pm 1.85 (\text{stat}) \pm 1.90 (\text{sys}) \, \text{km} \, \text{s}^{-1} \, \text{Mpc}^{-1}$$, notably consistent with the Cosmic Microwave Background (CMB) derived measurement of $H_0$ by Planck.

This finding is pivotal as it challenges earlier Cepheid-variable-based local $H_0$ estimations which report higher values, thereby potentially influencing interpretations surrounding the so-called "Hubble tension"—the discrepancy between $H_0$ values derived from early Universe observations versus local Universe measurements.

Implications and Future Directions

The research presents significant implications for both the practical measurement of cosmic distances and the theoretical landscape of cosmology. The JAGB calibration provides an alternate route for precise distance determination which aligns with fundamental physics. It is poised to play a critical role in revisiting Hubble constant measurements, possibly shedding light on various cosmological models, including the validity of the ΛCDM model.

Moreover, future developments in the field may focus on extending the JAGB methodology to additional galaxies using forthcoming data from high-resolution telescopes such as the Nancy Grace Roman Telescope and the continued utilization of JWST. Additionally, further empirical and theoretical investigations into the effects of metallicity and stellar population variances on JAGB stars could refine the method's robustness and accuracy, expanding the technique's applicability throughout cosmic history.

Conclusion

The paper by Lee et al. underscores the importance of novel calibration techniques like the JAGB method in refining our understanding of the Universe's expansion. By reinforcing distance scale accuracy and potentially resolving existing disputes regarding the Hubble constant, their work contributes meaningfully to cosmological measurements. As part of an evolving dialogue in modern astrophysics, these findings will likely guide future research endeavors and developments in distance measurement methodologies.