TDCOSMO: XX. WFI2033--4723, the First Quadruply-Imaged Quasar Modeled with JWST Imaging

Abstract: Gravitational time delays offer unique, independent measurements of the Hubble constant, $H_0$. Precise measurements of $H_0$ stand as one of the most pressing challenges in modern cosmology, and to do so with time delays requires precise lens models. While much work has focused on streamlining the modeling process to keep pace with the erumpent discovery of strongly-lensed systems, a critical step toward reducing uncertainty in $H_0$ comes from increasing the precision of individual lens models themselves. In this work, we demonstrate that the unprecedented imaging capabilities of JWST make this goal attainable. We present the first lens model for time-delay cosmography derived from JWST data, applied to the quadruply-imaged quasar WFI2033--4723. While the primary source of systematic uncertainty in time-delay cosmography is currently the mass-sheet degeneracy (MSD), the sensitivity of models to this MSD varies on how the point spread function (PSF) errors are mitigated. As the PSF is also the primary source of uncertainty in lens modeling, we focus on a comparison of different PSF modeling methods. Within the context of power-law models, we recover results in agreement with previous Hubble Space Telescope (HST)-based models, but with better precision of key lensing parameters through implementation of new PSF modeling techniques. Despite the record-holding precision of this system's HST modeling, we achieve an additional 22% increase in precision of the Fermat potential difference, directly reducing uncertainties of cosmological inference. These results would produce a 3% ($1\sigma$ of the modeling error) shift of $H_0$ towards a higher value for this lens, keeping all else constant. This work substantiates the groundbreaking potential of JWST for time-delay cosmography and lays the groundwork for modeling systems previously too faint to provide meaningful constraints on $H_0$.

Analyzing the Potential of JWST Imaging for Time-Delay Cosmography: Insights from TDCOSMO XX

The paper titled "TDCOSMO: XX. WFI2033–4723, the First Quadruply-Imaged Quasar Modeled with JWST Imaging," authored by D. M. Williams et al., provides new insights into the precision of time-delay cosmography, particularly in measuring the Hubble constant (H_0), by utilizing data from the James Webb Space Telescope (JWST). This study focuses on the quadruply-imaged quasar WFI2033–4723, presenting it as the first application of JWST imaging to gravitational lens modeling for cosmography.

Context and Rationale

Gravitational lensing, and specifically the delay in light travel time across different images (time-delay cosmography), offers a critical pathway to measure (H_0) independently of local distance ladder methods or cosmic microwave background inferences. Given the current tensions between different measurements of (H_0), resolving these discrepancies is crucial for cosmology. The key to reducing uncertainties in gravitational lens-based measurements lies in improving the precision of individual lens models. Here, the enhanced imaging capabilities of JWST come into play.

Methodology

The paper leverages the unprecedented resolution and sensitivity of the JWST, specifically its ability to provide detailed imaging of strongly lensed systems, to improve the precision of the lensing model of WFI2033–4723. The authors compare various Point Spread Function (PSF) modeling techniques and their consequences on the accuracy of the lens model, paying particular attention to mitigating errors related to the mass-sheet degeneracy (MSD) and PSF inaccuracies. This careful modeling approach allows for a more refined measurement of the Fermat potential—a core parameter in deriving (H_0).

Key Findings

1. Enhanced Precision: The JWST-based model of WFI2033 achieved a 22% increase in the precision of key lensing parameters compared to previous models based on Hubble Space Telescope (HST) data. This enhancement leads to more constrained estimates of the Fermat potential difference and a corresponding improvement in the determination of (H_0).

2. Mass-Sheet Degeneracy Mitigation: The study highlights how different PSF models, in conjunction with JWST’s high imaging quality, address the MSD, which remains the prominent source of systematic uncertainty in time-delay cosmography. The researchers found that despite the model improvements, the sensitivity to MSD varies among the PSF models used.

3. Reinforcement of HST Results: While JWST data reduced uncertainties, the results align well with previous HST-based models, providing validation for previous findings but with improved precision and confidence.

Implications and Future Directions

The findings underscore JWST's potential to transform gravitational lensing studies by reducing errors in (H_0) measurements, which could have profound implications for resolving the Hubble tension. For future work, the paper suggests extending these methodologies to fainter systems which, with JWST’s capabilities, can now be modelled with high precision. Enhanced PSF modeling and the integration of additional systems from future surveys such as the Large Synoptic Survey Telescope (LSST) and Euclid could further escalate the scale and precision of time-delay cosmography studies.

Conclusion

In summary, this study presents a substantial advancement in time-delay cosmography, demonstrating the JWST's capability to refine lens models and, consequently, the estimation of cosmological parameters such as (H_0). These advancements highlight the necessity of continued methodological developments and the increased reliance on superior astronomical datasets from next-generation observatories for progress in cosmological research.