Tip of the Red Giant Branch Distances with JWST. II. I-band Measurements in a Sample of Hosts of 10 SN Ia Match HST Cepheids (2408.00065v3)

Abstract: The Hubble Tension, a >5 sigma discrepancy between direct and indirect measurements of the Hubble constant (H0), has persisted for a decade and motivated intense scrutiny of the paths used to infer H0. 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 vs F090W-F150W) TRGB distances to 8 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 fourteen 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 0.01 to 0.03 mag, all consistent at 1 sigma 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 H0 that is competitive with the HST sample of 42 SNe Ia and 4 anchors; however, they already provide a vital systematic crosscheck to HST measurements of the distance ladder.

• The paper demonstrates that TRGB-based distances closely match HST Cepheid distances with a mean difference of 0.01 ± 0.04 mag.
• The paper employs robust I-band photometry via JWST across 14 method variants to ensure precise and stable distance measurements.
• The paper highlights that the current sample size limits a competitive Hubble constant determination, pointing to the need for further observations.

Tip of the Red Giant Branch Distances with JWST: An Examination of I-Band Measurements for SNe Ia Hosts

Introduction

This paper presents a comprehensive analysis of distances derived using the Tip of the Red Giant Branch (TRGB) method with observations from the James Webb Space Telescope (JWST). The paper specifically targets the I-band measurements for a series of galaxies hosting Type Ia Supernovae (SNe Ia), cross-referencing these with calibrated Cepheid distances from the Hubble Space Telescope (HST).

Methodology

The researchers utilized the I-band, deemed optimal for measuring the TRGB due to its stability against variations in stellar population age and metallicity, supported by theoretical models. Observations covered eight SNe Ia host galaxies, leveraging the maser host NGC 4258 as the geometric anchor for distance calibrations. The paper involved intricate photometric methods using JWST's NIRCam and comparisons with HST Cepheid-based distance moduli to verify consistency and identify potential systematic discrepancies.

Key Findings

• Distance Consistency: The analysis revealed no significant differences between the TRGB-based distances and the Cepheid-based distances, yielding a mean difference of 0.01 ± 0.04 (statistical) ± 0.04 (systematic) magnitudes.
• Robustness Across Variants: The TRGB analysis produced 14 method variants by modifying factors such as smoothing level and color range. The results consistently showed negligible differences, with a range between 0.00 to 0.02 mag.
• Insufficient Sample for Conclusive H0 Measurement: The currently small sample size limits the capability of deriving a competitive value for the Hubble constant (H0) using JWST alone, though these findings provide crucial checks against HST-derived results.

Theoretical and Practical Implications

1. Hubble Constant Tension: These findings confirm that there is no observable systematic bias in TRGB versus Cepheid distance measurements that could resolve the ongoing Hubble tension, a 5-6σ discrepancy between cosmological model-based and direct measurements of H0.
2. Cross-validation of Distance Indicators: The results emphasize the robustness of using both TRGB and Cepheid methods in distance calibrations, reinforcing their combined importance in cosmology.
3. Standard Candle Reliability: The paper supports TRGB as a reliable standard candle method that complements and cross-verifies the Cepheid-based ladder for distance measurements to extragalactic bodies.

Future Directions

Future work is encouraged to expand the sample size, allowing for more substantial contributions to the measurement of H0 via JWST. Further, developing other independent standard candles, such as Mira variables, could enhance the triangulation of these fundamental distance measures.

In summary, this research substantiates the accuracy of TRGB-based distances using JWST and aligns with Cepheid measures obtained via HST. It underpins the credibility of these methodologies while pointing toward necessary expansions for more comprehensive cosmological insights.