Cosmic Distances Calibrated to 1% Precision with Gaia EDR3 Parallaxes and Hubble Space Telescope Photometry of 75 Milky Way Cepheids Confirm Tension with LambdaCDM (2012.08534v2)

Abstract: We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, vastly improved since DR2, and the Period-Luminosity (PL) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe~Ia, it results in a measurement of the Hubble constant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid PL relation in the Milky Way, and the metallicity dependence of its zeropoint, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigma difference with the prediction from Planck CMB observations under LambdaCDM. We expect to reach ~1.3% precision in the near term from an expanded sample of ~40 SNe Ia in Cepheid hosts.

• The paper presents a novel calibration of Milky Way Cepheid distances to 1% precision using Gaia EDR3 parallaxes and HST photometry.
• The methodology refines the Period-Luminosity relation by leveraging high-fidelity, multi-filter observations to minimize systematic errors.
• The resulting distance ladder yields H₀ = 73.0 km/s/Mpc, highlighting a significant 4.2σ tension with ΛCDM predictions.

Precision Calibration of Cosmic Distances Using Milky Way Cepheids

In the pursuit of refining the Hubble constant (H$_0$), this paper presents a robust methodology for calibrating cosmic distances with unprecedented precision of 1% by utilizing updated parallax data from the European Space Agency's Gaia EDR3 and photometric measurements from the Hubble Space Telescope (HST) of 75 Cepheid variable stars located in the Milky Way. The research outlined in this document demonstrates an advanced approach to recalibrate the extragalactic distance ladder crucially underpinning contemporary cosmological measurements and asserts the presence of a tension with the standard $\Lambda$CDM model.

Methodology and Results

A vital process highlighted is the recalibration of the Period-Luminosity (P-L) relation exploiting the latest high-fidelity parallaxes from Gaia EDR3, which have seen significant improvements from previous data releases. Milky Way Cepheids' parallax measurements were scrutinized alongside their HST-captured photometric data using specific filters ({\it F555W}, {\it F814W}, {\it F160W}), minimizing systematic errors and mitigating issues such as saturation through the WFC3 spatial scanning mode. The dataset permitted a finely-tuned geometric calibration of Cepheid luminosities, achieving 1% precision, which stands as the best existing geometric anchor.

By harmonizing these recalibrated data with Type Ia supernovae, the research team determined an H$_0$ value of 73.0 km/s/Mpc. This value starkly contrasts with predictions derived from Planck CMB data under the standard $\Lambda$CDM model, revealing a notable 4.2$\sigma$ tension—an ongoing discrepancy known as the "Hubble tension."

Implications and Future Directions

The findings suggest that while Gaia EDR3 has significantly advanced the precision of parallax measurements, the identified residual parallax offset highlights potential areas for further methodological refinement. The concerns associated with parallax offset in brighter stars underpins the need for cautious interpretation and the importance of continual adjustment and validation of Gaia data, especially concerning amplitude and accuracy at the bright star end of their observable range.

The research also underscores the substantial potential of Gaia's upcoming data releases to further refine the cosmic distance ladder. With plans to extend the sample size to include Cepheids in approximately 40 supernovae hosts, there is a well-founded expectation of achieving precision nearing 1.3% in the short term, thus offering a clearer insight into cosmic expansion diagnostics.

Moreover, future iterations of the astrometric and photometric datasets from Gaia should allow for more precise determinations of H$_0$ by reducing systematic uncertainties in the distance measurement processes. This precision will be an invaluable asset in understanding the observed discrepancies in cosmological models, providing critical feedback to theoretical cosmology and potentially revealing new physics or adjustments needed in the current $\Lambda$CDM framework.

Conclusion

This paper reaffirms the critical role of precise distance calibrations in the overall endeavor to measure cosmic expansion rates. The usage of Gaia EDR3 and HST reinforces the value of multi-observatory data fusion and lays the groundwork for future escalations in precision, supporting a nuanced analysis of the Hubble tension. As methodologies continue to evolve, and data fidelity improves, the cosmological community anticipates enhanced resolution to some of the universe's most puzzling phenomena.