Current Challenges in Cepheid Distance Calibrations Using Gaia EDR3

Understand

Using parallaxes from Gaia Early Data Release 3 (EDR3), we determine multi-wavelength BVI, JHK, and [3.6] & [4.5] micron absolute magnitudes for 37 nearby Milky Way Cepheids, covering the period range between 5 and 60 days.

• We apply these period-luminosity relations to Cepheids in the Large and Small Magellanic Clouds, and find that the derived distances are significantly discrepant with the geometric distances according to detached eclipsing binaries (DEBs).
• We explore several potential causes of these issues, including reddening, metallicity, and the existence of an additional zero-point offset, but none provide a sufficient reconciliation with both DEB distances.
• We conclude that the combination of the systematic uncertainties on the EDR3 parallaxes with the uncertainties on the effect of metallicity on the Cepheid distance scale leads to a systematic error floor of approximately 3%.