A distance to the Large Magellanic Cloud that is precise to one per cent

Abstract: In the era of precision cosmology, it is essential to empirically determine the Hubble constant with an accuracy of one per cent or better. At present, the uncertainty on this constant is dominated by the uncertainty in the calibration of the Cepheid period - luminosity relationship (also known as Leavitt Law). The Large Magellanic Cloud has traditionally served as the best galaxy with which to calibrate Cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale. Eclipsing binary systems composed of late-type stars offer the most precise and accurate way to measure the distance to the Large Magellanic Cloud. Currently the limit of the precision attainable with this technique is about two per cent, and is set by the precision of the existing calibrations of the surface brightness - colour relation. Here we report the calibration of the surface brightness-colour relation with a precision of 0.8 per cent. We use this calibration to determine the geometrical distance to the Large Magellanic Cloud that is precise to 1 per cent based on 20 eclipsing binary systems. The final distane is 49.59 +/- 0.09 (statistical) +/- 0.54 (systematic) kiloparsecs.

• The paper presents a refined method using eclipsing binaries to measure the LMC distance with an unprecedented 0.8% calibration precision.
• It leverages precise angular diameter measurements and near-infrared photometry of red clump giants to enhance the reliability of distance estimates.
• This advancement tightens the Cepheid period-luminosity calibration, addressing the Hubble tension and improving extragalactic distance scaling.

Precise Determination of the Distance to the Large Magellanic Cloud

The paper offers a sophisticated and highly precise methodological enhancement in determining the distance to the Large Magellanic Cloud (LMC). Within the domain of precision cosmology, accurately calibrating the Cepheid period-luminosity (P–L) relationship is pivotal, directly impacting the evaluation of the Hubble constant. Traditionally, the LMC serves as a significant anchor in the extragalactic distance scale calibration due to its advantageous placement and the availability of numerous standard candles, including Cepheid variables.

This research employs a refined approach using eclipsing binary systems composed of late-type stars to establish the geometric distance to the LMC with unprecedented precision. Specifically, the paper reports a calibration of the surface brightness-colour relation achieving a precision of 0.8%. Using this calibration, the researchers determine the distance to the LMC from 20 eclipsing binary systems to be 49.59 ± 0.09 (statistical) ± 0.54 (systematic) kiloparsecs, translating to a distance modulus of 18.477 ± 0.004 (statistical) ± 0.026 (systematic) mag.

Key to this achievement is the precise measurement of stellar angular diameters and near-infrared photometry of 41 carefully chosen nearby red clump giant stars, avoiding variable stars or binaries. The derived relationship, based on the least-squares fit:

$$S_V = (1.330 ± 0.017) \times [(V − K) − 0.405] + (5.869 ± 0.003) \text{ mag}$$

demonstrates a root-mean-square scatter of 0.018 mag, confirming a distance measurement precision for these systems notably more accurate than existing methodologies.

The study carries substantial theoretical and practical implications. By narrowing uncertainties, the research contributes significantly to discussions around the Hubble tension—a discrepancy in values of the Hubble constant as measured through different cosmic tools. Furthermore, the method strengthens the reliability of the LMC as a cosmic distance ladder cornerstone, independent of metallicity and gravity influences, thus paving the way for accurate extragalactic measurements. The calibration impact extends to improving the reliability of Cepheid P-L relation calibrations, crucial for supernova Ia studies and, by extension, a refined universe expansion rate.

Moreover, this advanced measurement technique of the LMC distance is anticipated to become an essential tool alongside upcoming astronomical missions, such as Gaia, providing consistency checks and potentially serving as a benchmark against which other methods, including parallax, are examined.

Future developments may see this calibration applied broadly to other nearby dwarf galaxies, solidifying the accuracy of the extragalactic distance scale. This methodology positions itself to further refine the absolute distance zero point for Cepheids, driving advancements in cosmic scale research and enriching our understanding of fundamental cosmology principles encompassing both local and universal scales.