Current Challenges in Cepheid Distance Calibrations Using Gaia EDR3

TL;DR

This study assesses Gaia EDR3 parallaxes for Cepheids, revealing significant discrepancies in distance measurements and highlighting systematic uncertainties that limit current precision for extragalactic distance calibration.

Contribution

It provides a detailed analysis of Gaia EDR3 data for Cepheids, identifying systematic errors and limitations in achieving 1% distance accuracy.

Findings

Discrepancies between Gaia-based and eclipsing binary distances

Systematic error floor of approximately 3% due to uncertainties

Gaia EDR3 data currently insufficient for 1% extragalactic distance precision

Abstract

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%. We therefore find that the EDR3 data is not sufficiently accurate in the regime of these bright Cepheids to determine extragalactic distances precise to the 1% level at this time, in agreement with a number of contemporary studies.