Assess potential galaxy-to-galaxy and modeling systematics in the NGC 4258 maser distance anchor

Ascertain whether underlying galaxy-to-galaxy differences in the H2O megamaser geometric distance method and systematics tied to maser-disk modeling assumptions affect the NGC 4258 distance used to calibrate the JWST Cepheid, TRGB, and JAGB zero points, and quantify their contribution to the H0 error budget.

Background

All three distance indicators (Cepheids, TRGB, JAGB) in this work are zero-point calibrated to the geometric maser distance of NGC 4258. This choice ensures uniformity across methods but also concentrates any systematic errors specific to the maser technique or to NGC 4258 itself.

Because NGC 4258 is currently the only nearby maser host with the requisite geometry and precision, the authors note that it is not currently possible to evaluate potential galaxy-to-galaxy variations in maser distances or assess modeling-assumption systematics. Establishing these effects requires additional independent anchors or more maser hosts with comparable precision.