Cause of the systematic offset between MagE and H3 spectroscopic distance scales

Determine the cause of the approximately 5% systematic offset between spectroscopic distances derived from Magellan/MagE observations and those from the H3 Survey, including whether it arises from a ≈0.1 dex metallicity scale difference in the MagE analysis.

Background

The authors cross-validated spectroscopic distances using H3 and MagE data, as well as stellar distances for the Sextans and Crater 2 dwarf galaxies, and found reliable distances out to ≳100 kpc. They identified a ~5% systematic offset between the H3 and MagE spectroscopic distance scales, possibly linked to a ~0.1 dex difference in the metallicity scale.

While they verified that this offset has negligible impact on the main results and adopted appropriate uncertainty floors, the precise origin of the offset remains unresolved. Clarifying the underlying cause will improve calibration and consistency across surveys.